[RFC v2 1/5] drm/nouveau/kms/nv40-/backlight: Assign prop type once

[RFC v2 1/5] drm/nouveau/kms/nv40-/backlight: Assign prop type once

[Lyude Paul]

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: greg.depoire@gmail.com
---
 drivers/gpu/drm/nouveau/nouveau_backlight.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c b/drivers/gpu/drm/nouveau/nouveau_backlight.c
index 72f35a2babcb..42b498e7e2bf 100644
--- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
+++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c
@@ -106,7 +106,6 @@ nv40_backlight_init(struct nouveau_encoder *encoder,
 	if (!(nvif_rd32(device, NV40_PMC_BACKLIGHT) & NV40_PMC_BACKLIGHT_MASK))
 		return -ENODEV;
 
-	props->type = BACKLIGHT_RAW;
 	props->max_brightness = 31;
 	*ops = &nv40_bl_ops;
 	return 0;
@@ -212,7 +211,6 @@ nv50_backlight_init(struct nouveau_encoder *nv_encoder,
 	else
 		*ops = &nva3_bl_ops;
 
-	props->type = BACKLIGHT_RAW;
 	props->max_brightness = 100;
 
 	return 0;
@@ -226,7 +224,7 @@ nouveau_backlight_init(struct drm_connector *connector)
 	struct nouveau_encoder *nv_encoder = NULL;
 	struct nvif_device *device = &drm->client.device;
 	char backlight_name[BL_NAME_SIZE];
-	struct backlight_properties props = {0};
+	struct backlight_properties props = { .type = BACKLIGHT_RAW, 0 };
 	const struct backlight_ops *ops;
 	int ret;
 
-- 
2.29.2

[RFC v2 2/5] drm/nouveau/kms: Don't probe eDP connectors more then once

[Lyude Paul]

eDP doesn't do hotplugging, so there's no reason for us to reprobe it (unless a
connection status change is being forced, of course).

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: greg.depoire@gmail.com
---
 drivers/gpu/drm/nouveau/nouveau_connector.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nouveau_connector.c b/drivers/gpu/drm/nouveau/nouveau_connector.c
index 14c29e68db8f..f4d16576a7da 100644
--- a/drivers/gpu/drm/nouveau/nouveau_connector.c
+++ b/drivers/gpu/drm/nouveau/nouveau_connector.c
@@ -556,6 +556,12 @@ nouveau_connector_detect(struct drm_connector *connector, bool force)
 	int ret;
 	enum drm_connector_status conn_status = connector_status_disconnected;
 
+	/* eDP doesn't do hotplugging, never probe more then once */
+	if (nv_connector->type == DCB_CONNECTOR_eDP &&
+	    connector->force == DRM_FORCE_UNSPECIFIED &&
+	    connector->status != connector_status_unknown)
+		return connector->status;
+
 	/* Outputs are only polled while runtime active, so resuming the
 	 * device here is unnecessary (and would deadlock upon runtime suspend
 	 * because it waits for polling to finish). We do however, want to
-- 
2.29.2

[RFC v2 3/5] drm/i915/dp: Remove redundant AUX backlight frequency calculations

[Lyude Paul]

Noticed this while moving all of the VESA backlight code in i915 over to
DRM helpers: it would appear that we calculate the frequency value we want
to write to DP_EDP_BACKLIGHT_FREQ_SET twice even though this value never
actually changes during runtime. So, let's simplify things by just caching
this value in intel_panel.backlight, and re-writing it as-needed.

Changes since v1:
* Wrap panel->backlight.edp.vesa.pwm_freq_pre_divider in
  DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP check - Jani

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: greg.depoire@gmail.com
---
 .../drm/i915/display/intel_display_types.h    |  1 +
 .../drm/i915/display/intel_dp_aux_backlight.c | 65 ++++++-------------
 2 files changed, 20 insertions(+), 46 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index 927a8aeae324..8450ab8fb245 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -264,6 +264,7 @@ struct intel_panel {
 		union {
 			struct {
 				u8 pwmgen_bit_count;
+				u8 pwm_freq_pre_divider;
 			} vesa;
 			struct {
 				bool sdr_uses_aux;
diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
index 651884390137..62294967f430 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -373,50 +373,6 @@ intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state,
 	}
 }
 
-/*
- * Set PWM Frequency divider to match desired frequency in vbt.
- * The PWM Frequency is calculated as 27Mhz / (F x P).
- * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
- *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
- * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
- *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
- */
-static bool intel_dp_aux_vesa_set_pwm_freq(struct intel_connector *connector)
-{
-	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
-	struct intel_dp *intel_dp = intel_attached_dp(connector);
-	const u8 pn = connector->panel.backlight.edp.vesa.pwmgen_bit_count;
-	int freq, fxp, f, fxp_actual, fxp_min, fxp_max;
-
-	freq = dev_priv->vbt.backlight.pwm_freq_hz;
-	if (!freq) {
-		drm_dbg_kms(&dev_priv->drm,
-			    "Use panel default backlight frequency\n");
-		return false;
-	}
-
-	fxp = DIV_ROUND_CLOSEST(KHz(DP_EDP_BACKLIGHT_FREQ_BASE_KHZ), freq);
-	f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
-	fxp_actual = f << pn;
-
-	/* Ensure frequency is within 25% of desired value */
-	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
-	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
-
-	if (fxp_min > fxp_actual || fxp_actual > fxp_max) {
-		drm_dbg_kms(&dev_priv->drm, "Actual frequency out of range\n");
-		return false;
-	}
-
-	if (drm_dp_dpcd_writeb(&intel_dp->aux,
-			       DP_EDP_BACKLIGHT_FREQ_SET, (u8) f) < 0) {
-		drm_dbg_kms(&dev_priv->drm,
-			    "Failed to write aux backlight freq\n");
-		return false;
-	}
-	return true;
-}
-
 static void
 intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
 				   const struct drm_connector_state *conn_state, u32 level)
@@ -459,9 +415,13 @@ intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
 		break;
 	}
 
-	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
-		if (intel_dp_aux_vesa_set_pwm_freq(connector))
+	if (panel->backlight.edp.vesa.pwm_freq_pre_divider) {
+		if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_BACKLIGHT_FREQ_SET,
+				       panel->backlight.edp.vesa.pwm_freq_pre_divider) == 1)
 			new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
+		else
+			drm_dbg_kms(&i915->drm, "Failed to write aux backlight frequency\n");
+	}
 
 	if (new_dpcd_buf != dpcd_buf) {
 		if (drm_dp_dpcd_writeb(&intel_dp->aux,
@@ -482,6 +442,14 @@ static void intel_dp_aux_vesa_disable_backlight(const struct drm_connector_state
 				  false);
 }
 
+/*
+ * Compute PWM frequency divider value based off the frequency provided to us by the vbt.
+ * The PWM Frequency is calculated as 27Mhz / (F x P).
+ * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
+ *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
+ * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
+ *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
+ */
 static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connector)
 {
 	struct drm_i915_private *i915 = to_i915(connector->base.dev);
@@ -533,8 +501,10 @@ static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connecto
 	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
 	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
 
+	/* Ensure frequency is within 25% of desired value */
 	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
 	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
+
 	if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
 		drm_dbg_kms(&i915->drm,
 			    "VBT defined backlight frequency out of range\n");
@@ -555,7 +525,10 @@ static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connecto
 			    "Failed to write aux pwmgen bit count\n");
 		return max_backlight;
 	}
+
 	panel->backlight.edp.vesa.pwmgen_bit_count = pn;
+	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
+		panel->backlight.edp.vesa.pwm_freq_pre_divider = f;
 
 	max_backlight = (1 << pn) - 1;
 
-- 
2.29.2

[RFC v2 4/5] drm/dp: Extract i915's eDP backlight code into DRM helpers

[Lyude Paul]

Since we're about to implement eDP backlight support in nouveau using the
standard protocol from VESA, we might as well just take the code that's
already written for this and move it into a set of shared DRM helpers.

Note that these helpers are intended to handle DPCD related backlight
control bits such as setting the brightness level over AUX, probing the
backlight's TCON, enabling/disabling the backlight over AUX if supported,
etc. Any PWM-related portions of backlight control are explicitly left up
to the driver, as these will vary from platform to platform.

The only exception to this is the calculation of the PWM frequency
pre-divider value. This is because the only platform-specific information
required for this is the PWM frequency of the panel, which the driver is
expected to provide if available. The actual algorithm for calculating this
value is standard and is defined in the eDP specification from VESA.

Note that these helpers do not yet implement the full range of features
the VESA backlight interface provides, and only provide the following
functionality (all of which was already present in i915's DPCD backlight
support):

* Basic control of brightness levels
* Basic probing of backlight capabilities
* Helpers for enabling and disabling the backlight

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: greg.depoire@gmail.com
---
 drivers/gpu/drm/drm_dp_helper.c               | 332 ++++++++++++++++++
 .../drm/i915/display/intel_display_types.h    |   3 +-
 .../drm/i915/display/intel_dp_aux_backlight.c | 288 ++-------------
 include/drm/drm_dp_helper.h                   |  48 +++
 4 files changed, 413 insertions(+), 258 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index eedbb48815b7..04cb2b6970a8 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -3082,3 +3082,335 @@ int drm_dp_pcon_convert_rgb_to_ycbcr(struct drm_dp_aux *aux, u8 color_spc)
 	return 0;
 }
 EXPORT_SYMBOL(drm_dp_pcon_convert_rgb_to_ycbcr);
+
+/**
+ * drm_edp_backlight_set_level() - Set the backlight level of an eDP panel via AUX
+ * @aux: The DP AUX channel to use
+ * @bl: Backlight capability info from drm_edp_backlight_init()
+ * @level: The brightness level to set
+ *
+ * Sets the brightness level of an eDP panel's backlight. Note that the panel's backlight must
+ * already have been enabled by the driver by calling drm_edp_backlight_enable().
+ *
+ * Returns: %0 on success, negative error code on failure
+ */
+int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
+				u16 level)
+{
+	int ret;
+	u8 buf[2] = { 0 };
+
+	if (bl->lsb_reg_used) {
+		buf[0] = (level & 0xFF00) >> 8;
+		buf[1] = (level & 0x00FF);
+	} else {
+		buf[0] = level;
+	}
+
+	ret = drm_dp_dpcd_write(aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB, buf, sizeof(buf));
+	if (ret != sizeof(buf)) {
+		DRM_ERROR("%s: Failed to write aux backlight level: %d\n", aux->name, ret);
+		return ret < 0 ? ret : -EIO;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_edp_backlight_set_level);
+
+static int
+drm_edp_backlight_set_enable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
+			     bool enable)
+{
+	int ret;
+	u8 buf;
+
+	/* The panel uses something other then DPCD for enabling it's backlight */
+	if (!bl->aux_enable)
+		return 0;
+
+	ret = drm_dp_dpcd_readb(aux, DP_EDP_DISPLAY_CONTROL_REGISTER, &buf);
+	if (ret != 1) {
+		DRM_ERROR("%s: Failed to read eDP display control register: %d\n", aux->name, ret);
+		return ret < 0 ? ret : -EIO;
+	}
+	if (enable)
+		buf |= DP_EDP_BACKLIGHT_ENABLE;
+	else
+		buf &= ~DP_EDP_BACKLIGHT_ENABLE;
+
+	ret = drm_dp_dpcd_writeb(aux, DP_EDP_DISPLAY_CONTROL_REGISTER, buf);
+	if (ret != 1) {
+		DRM_ERROR("%s: Failed to write eDP display control register: %d\n", aux->name, ret);
+		return ret < 0 ? ret : -EIO;
+	}
+
+	return 0;
+}
+
+/**
+ * drm_edp_backlight_enable() - Enable an eDP panel's backlight using DPCD
+ * @aux: The DP AUX channel to use
+ * @bl: Backlight capability info from drm_edp_backlight_init()
+ * @level: The initial backlight level to set via AUX, if there is one
+ *
+ * This function handles enabling DPCD backlight controls on a panel over DPCD, while additionally
+ * restoring any important backlight state such as the given backlight level, the brightness byte
+ * count, backlight frequency, etc.
+ *
+ * Note that certain panels, while supporting brightness level controls over DPCD, may not support
+ * having their backlights enabled via the standard %DP_EDP_DISPLAY_CONTROL_REGISTER. On such panels
+ * &drm_edp_backlight_info.aux_enable will be set to %false, this function will skip the step of
+ * programming the %DP_EDP_DISPLAY_CONTROL_REGISTER, and the driver must perform the required
+ * implementation specific step for enabling the backlight after calling this function.
+ *
+ * Returns: %0 on success, negative error code on failure.
+ */
+int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
+			     const u16 level)
+{
+	int ret;
+	u8 dpcd_buf, new_dpcd_buf;
+
+	ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf);
+	if (ret != 1) {
+		DRM_DEBUG_KMS("%s: Failed to read backlight mode: %d\n", aux->name, ret);
+		return ret < 0 ? ret : -EIO;
+	}
+
+	new_dpcd_buf = dpcd_buf;
+
+	if ((dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) != DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
+		new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
+		new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
+
+		ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, bl->pwmgen_bit_count);
+		if (ret != 1)
+			DRM_DEBUG_KMS("%s: Failed to write aux pwmgen bit count: %d\n",
+				      aux->name, ret);
+	}
+
+	if (bl->pwm_freq_pre_divider) {
+		ret = drm_dp_dpcd_writeb(aux, DP_EDP_BACKLIGHT_FREQ_SET, bl->pwm_freq_pre_divider);
+		if (ret != 1)
+			DRM_DEBUG_KMS("%s: Failed to write aux backlight frequency: %d\n",
+				      aux->name, ret);
+		else
+			new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
+	}
+
+	if (new_dpcd_buf != dpcd_buf) {
+		ret = drm_dp_dpcd_writeb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf);
+		if (ret != 1) {
+			DRM_DEBUG_KMS("%s: Failed to write aux backlight mode: %d\n",
+				      aux->name, ret);
+			return ret < 0 ? ret : -EIO;
+		}
+	}
+
+	ret = drm_edp_backlight_set_level(aux, bl, level);
+	if (ret < 0)
+		return ret;
+	ret = drm_edp_backlight_set_enable(aux, bl, true);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_edp_backlight_enable);
+
+/**
+ * drm_edp_backlight_disable() - Disable an eDP backlight using DPCD, if supported
+ * @aux: The DP AUX channel to use
+ * @bl: Backlight capability info from drm_edp_backlight_init()
+ *
+ * This function handles disabling DPCD backlight controls on a panel over AUX. Note that some
+ * panels have backlights that are enabled/disabled by other means, despite having their brightness
+ * values controlled through DPCD. On such panels &drm_edp_backlight_info.aux_enable will be set to
+ * %false, this function will become a no-op (and we will skip updating
+ * %DP_EDP_DISPLAY_CONTROL_REGISTER), and the driver must take care to perform it's own
+ * implementation specific step for disabling the backlight.
+ *
+ * Returns: %0 on success or no-op, negative error code on failure.
+ */
+int drm_edp_backlight_disable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl)
+{
+	int ret;
+
+	ret = drm_edp_backlight_set_enable(aux, bl, false);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_edp_backlight_disable);
+
+static inline int
+drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl,
+			    u16 driver_pwm_freq_hz, const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE])
+{
+	int fxp, fxp_min, fxp_max, fxp_actual, f = 1;
+	int ret;
+	u8 pn, pn_min, pn_max;
+
+	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT, &pn);
+	if (ret != 1) {
+		DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap: %d\n", aux->name, ret);
+		return -ENODEV;
+	}
+
+	pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
+	bl->max = (1 << pn) - 1;
+	if (!driver_pwm_freq_hz)
+		return 0;
+
+	/*
+	 * Set PWM Frequency divider to match desired frequency provided by the driver.
+	 * The PWM Frequency is calculated as 27Mhz / (F x P).
+	 * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
+	 *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
+	 * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
+	 *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
+	 */
+
+	/* Find desired value of (F x P)
+	 * Note that, if F x P is out of supported range, the maximum value or minimum value will
+	 * applied automatically. So no need to check that.
+	 */
+	fxp = DIV_ROUND_CLOSEST(1000 * DP_EDP_BACKLIGHT_FREQ_BASE_KHZ, driver_pwm_freq_hz);
+
+	/* Use highest possible value of Pn for more granularity of brightness adjustment while
+	 * satifying the conditions below.
+	 * - Pn is in the range of Pn_min and Pn_max
+	 * - F is in the range of 1 and 255
+	 * - FxP is within 25% of desired value.
+	 *   Note: 25% is arbitrary value and may need some tweak.
+	 */
+	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min);
+	if (ret != 1) {
+		DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap min: %d\n", aux->name, ret);
+		return 0;
+	}
+	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max);
+	if (ret != 1) {
+		DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap max: %d\n", aux->name, ret);
+		return 0;
+	}
+	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
+	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
+
+	/* Ensure frequency is within 25% of desired value */
+	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
+	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
+	if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
+		DRM_DEBUG_KMS("%s: Driver defined backlight frequency (%d) out of range\n",
+			      aux->name, driver_pwm_freq_hz);
+		return 0;
+	}
+
+	for (pn = pn_max; pn >= pn_min; pn--) {
+		f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
+		fxp_actual = f << pn;
+		if (fxp_min <= fxp_actual && fxp_actual <= fxp_max)
+			break;
+	}
+
+	ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, pn);
+	if (ret != 1) {
+		DRM_DEBUG_KMS("%s: Failed to write aux pwmgen bit count: %d\n", aux->name, ret);
+		return 0;
+	}
+	bl->pwmgen_bit_count = pn;
+	bl->max = (1 << pn) - 1;
+
+	if (edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP) {
+		bl->pwm_freq_pre_divider = f;
+		DRM_DEBUG_KMS("%s: Using backlight frequency from driver (%dHz)\n",
+			      aux->name, driver_pwm_freq_hz);
+	}
+
+	return 0;
+}
+
+static inline int
+drm_edp_backlight_probe_level(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl,
+			      u8 *current_mode)
+{
+	int ret;
+	u8 buf[2];
+	u8 mode_reg;
+
+	ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &mode_reg);
+	if (ret != 1) {
+		DRM_DEBUG_KMS("%s: Failed to read backlight mode: %d\n", aux->name, ret);
+		return ret < 0 ? ret : -EIO;
+	}
+
+	*current_mode = (mode_reg & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK);
+	if (*current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
+		int size = 1 + bl->lsb_reg_used;
+
+		ret = drm_dp_dpcd_read(aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB, buf, size);
+		if (ret != size) {
+			DRM_DEBUG_KMS("%s: Failed to read backlight level: %d\n", aux->name, ret);
+			return ret < 0 ? ret : -EIO;
+		}
+
+		if (bl->lsb_reg_used)
+			return (buf[0] << 8) | buf[1];
+		else
+			return buf[0];
+	}
+
+	/*
+	 * If we're not in DPCD control mode yet, the programmed brightness value is meaningless and
+	 * the driver should assume max brightness
+	 */
+	return bl->max;
+}
+
+/**
+ * drm_edp_backlight_init() - Probe a display panel's TCON using the standard VESA eDP backlight
+ * interface.
+ * @aux: The DP aux device to use for probing
+ * @bl: The &drm_edp_backlight_info struct to fill out with information on the backlight
+ * @driver_pwm_freq_hz: Optional PWM frequency from the driver in hz
+ * @edp_dpcd: A cached copy of the eDP DPCD
+ * @current_level: Where to store the probed brightness level
+ * @current_mode: Where to store the currently set backlight control mode
+ *
+ * Initializes a &drm_edp_backlight_info struct by probing @aux for it's backlight capabilities,
+ * along with also probing the current and maximum supported brightness levels.
+ *
+ * If @driver_pwm_freq_hz is non-zero, this will be used as the backlight frequency. Otherwise, the
+ * default frequency from the panel is used.
+ *
+ * Returns: %0 on success, negative error code on failure.
+ */
+int
+drm_edp_backlight_init(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl,
+		       u16 driver_pwm_freq_hz, const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE],
+		       u16 *current_level, u8 *current_mode)
+{
+	int ret;
+
+	if (edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP)
+		bl->aux_enable = true;
+	if (edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
+		bl->lsb_reg_used = true;
+
+	ret = drm_edp_backlight_probe_max(aux, bl, driver_pwm_freq_hz, edp_dpcd);
+	if (ret < 0)
+		return ret;
+
+	ret = drm_edp_backlight_probe_level(aux, bl, current_mode);
+	if (ret < 0)
+		return ret;
+	*current_level = ret;
+
+	DRM_DEBUG_KMS("%s: Found backlight level=%d/%d pwm_freq_pre_divider=%d mode=%x\n",
+		      aux->name, *current_level, bl->max, bl->pwm_freq_pre_divider, *current_mode);
+	DRM_DEBUG_KMS("%s: Backlight caps: pwmgen_bit_count=%d lsb_reg_used=%d aux_enable=%d\n",
+		      aux->name, bl->pwmgen_bit_count, bl->lsb_reg_used, bl->aux_enable);
+	return 0;
+}
+EXPORT_SYMBOL(drm_edp_backlight_init);
diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index 8450ab8fb245..2af208f1b467 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -263,8 +263,7 @@ struct intel_panel {
 		/* DPCD backlight */
 		union {
 			struct {
-				u8 pwmgen_bit_count;
-				u8 pwm_freq_pre_divider;
+				struct drm_edp_backlight_info info;
 			} vesa;
 			struct {
 				bool sdr_uses_aux;
diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
index 62294967f430..1ae14bc9e3fe 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -268,109 +268,19 @@ intel_dp_aux_hdr_setup_backlight(struct intel_connector *connector, enum pipe pi
 }
 
 /* VESA backlight callbacks */
-static void set_vesa_backlight_enable(struct intel_dp *intel_dp, bool enable)
-{
-	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
-	u8 reg_val = 0;
-
-	/* Early return when display use other mechanism to enable backlight. */
-	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP))
-		return;
-
-	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
-			      &reg_val) < 0) {
-		drm_dbg_kms(&i915->drm, "Failed to read DPCD register 0x%x\n",
-			    DP_EDP_DISPLAY_CONTROL_REGISTER);
-		return;
-	}
-	if (enable)
-		reg_val |= DP_EDP_BACKLIGHT_ENABLE;
-	else
-		reg_val &= ~(DP_EDP_BACKLIGHT_ENABLE);
-
-	if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
-			       reg_val) != 1) {
-		drm_dbg_kms(&i915->drm, "Failed to %s aux backlight\n",
-			    enable ? "enable" : "disable");
-	}
-}
-
-static bool intel_dp_aux_vesa_backlight_dpcd_mode(struct intel_connector *connector)
-{
-	struct intel_dp *intel_dp = intel_attached_dp(connector);
-	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
-	u8 mode_reg;
-
-	if (drm_dp_dpcd_readb(&intel_dp->aux,
-			      DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
-			      &mode_reg) != 1) {
-		drm_dbg_kms(&i915->drm,
-			    "Failed to read the DPCD register 0x%x\n",
-			    DP_EDP_BACKLIGHT_MODE_SET_REGISTER);
-		return false;
-	}
-
-	return (mode_reg & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) ==
-	       DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
-}
-
-/*
- * Read the current backlight value from DPCD register(s) based
- * on if 8-bit(MSB) or 16-bit(MSB and LSB) values are supported
- */
 static u32 intel_dp_aux_vesa_get_backlight(struct intel_connector *connector, enum pipe unused)
 {
-	struct intel_dp *intel_dp = intel_attached_dp(connector);
-	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
-	u8 read_val[2] = { 0x0 };
-	u16 level = 0;
-
-	/*
-	 * If we're not in DPCD control mode yet, the programmed brightness
-	 * value is meaningless and we should assume max brightness
-	 */
-	if (!intel_dp_aux_vesa_backlight_dpcd_mode(connector))
-		return connector->panel.backlight.max;
-
-	if (drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
-			     &read_val, sizeof(read_val)) < 0) {
-		drm_dbg_kms(&i915->drm, "Failed to read DPCD register 0x%x\n",
-			    DP_EDP_BACKLIGHT_BRIGHTNESS_MSB);
-		return 0;
-	}
-	level = read_val[0];
-	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
-		level = (read_val[0] << 8 | read_val[1]);
-
-	return level;
+	return connector->panel.backlight.level;
 }
 
-/*
- * Sends the current backlight level over the aux channel, checking if its using
- * 8-bit or 16 bit value (MSB and LSB)
- */
 static void
-intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state,
-				u32 level)
+intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state, u32 level)
 {
 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
-	struct intel_dp *intel_dp = intel_attached_dp(connector);
-	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
-	u8 vals[2] = { 0x0 };
-
-	vals[0] = level;
+	struct intel_panel *panel = &connector->panel;
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
 
-	/* Write the MSB and/or LSB */
-	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT) {
-		vals[0] = (level & 0xFF00) >> 8;
-		vals[1] = (level & 0xFF);
-	}
-	if (drm_dp_dpcd_write(&intel_dp->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
-			      vals, sizeof(vals)) < 0) {
-		drm_dbg_kms(&i915->drm,
-			    "Failed to write aux backlight level\n");
-		return;
-	}
+	drm_edp_backlight_set_level(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
 }
 
 static void
@@ -378,176 +288,46 @@ intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
 				   const struct drm_connector_state *conn_state, u32 level)
 {
 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
-	struct intel_dp *intel_dp = intel_attached_dp(connector);
-	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 	struct intel_panel *panel = &connector->panel;
-	u8 dpcd_buf, new_dpcd_buf, edp_backlight_mode;
-	u8 pwmgen_bit_count = panel->backlight.edp.vesa.pwmgen_bit_count;
-
-	if (drm_dp_dpcd_readb(&intel_dp->aux,
-			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) != 1) {
-		drm_dbg_kms(&i915->drm, "Failed to read DPCD register 0x%x\n",
-			    DP_EDP_BACKLIGHT_MODE_SET_REGISTER);
-		return;
-	}
-
-	new_dpcd_buf = dpcd_buf;
-	edp_backlight_mode = dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
-
-	switch (edp_backlight_mode) {
-	case DP_EDP_BACKLIGHT_CONTROL_MODE_PWM:
-	case DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET:
-	case DP_EDP_BACKLIGHT_CONTROL_MODE_PRODUCT:
-		new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
-		new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
-
-		if (drm_dp_dpcd_writeb(&intel_dp->aux,
-				       DP_EDP_PWMGEN_BIT_COUNT,
-				       pwmgen_bit_count) < 0)
-			drm_dbg_kms(&i915->drm,
-				    "Failed to write aux pwmgen bit count\n");
-
-		break;
-
-	/* Do nothing when it is already DPCD mode */
-	case DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD:
-	default:
-		break;
-	}
-
-	if (panel->backlight.edp.vesa.pwm_freq_pre_divider) {
-		if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_BACKLIGHT_FREQ_SET,
-				       panel->backlight.edp.vesa.pwm_freq_pre_divider) == 1)
-			new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
-		else
-			drm_dbg_kms(&i915->drm, "Failed to write aux backlight frequency\n");
-	}
-
-	if (new_dpcd_buf != dpcd_buf) {
-		if (drm_dp_dpcd_writeb(&intel_dp->aux,
-			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf) < 0) {
-			drm_dbg_kms(&i915->drm,
-				    "Failed to write aux backlight mode\n");
-		}
-	}
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
 
-	intel_dp_aux_vesa_set_backlight(conn_state, level);
-	set_vesa_backlight_enable(intel_dp, true);
+	drm_edp_backlight_enable(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
 }
 
 static void intel_dp_aux_vesa_disable_backlight(const struct drm_connector_state *old_conn_state,
 						u32 level)
 {
-	set_vesa_backlight_enable(enc_to_intel_dp(to_intel_encoder(old_conn_state->best_encoder)),
-				  false);
-}
-
-/*
- * Compute PWM frequency divider value based off the frequency provided to us by the vbt.
- * The PWM Frequency is calculated as 27Mhz / (F x P).
- * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
- *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
- * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
- *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
- */
-static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connector)
-{
-	struct drm_i915_private *i915 = to_i915(connector->base.dev);
-	struct intel_dp *intel_dp = intel_attached_dp(connector);
+	struct intel_connector *connector = to_intel_connector(old_conn_state->connector);
 	struct intel_panel *panel = &connector->panel;
-	u32 max_backlight = 0;
-	int freq, fxp, fxp_min, fxp_max, fxp_actual, f = 1;
-	u8 pn, pn_min, pn_max;
-
-	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT, &pn) == 1) {
-		pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
-		max_backlight = (1 << pn) - 1;
-	}
-
-	/* Find desired value of (F x P)
-	 * Note that, if F x P is out of supported range, the maximum value or
-	 * minimum value will applied automatically. So no need to check that.
-	 */
-	freq = i915->vbt.backlight.pwm_freq_hz;
-	drm_dbg_kms(&i915->drm, "VBT defined backlight frequency %u Hz\n",
-		    freq);
-	if (!freq) {
-		drm_dbg_kms(&i915->drm,
-			    "Use panel default backlight frequency\n");
-		return max_backlight;
-	}
-
-	fxp = DIV_ROUND_CLOSEST(KHz(DP_EDP_BACKLIGHT_FREQ_BASE_KHZ), freq);
-
-	/* Use highest possible value of Pn for more granularity of brightness
-	 * adjustment while satifying the conditions below.
-	 * - Pn is in the range of Pn_min and Pn_max
-	 * - F is in the range of 1 and 255
-	 * - FxP is within 25% of desired value.
-	 *   Note: 25% is arbitrary value and may need some tweak.
-	 */
-	if (drm_dp_dpcd_readb(&intel_dp->aux,
-			      DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min) != 1) {
-		drm_dbg_kms(&i915->drm,
-			    "Failed to read pwmgen bit count cap min\n");
-		return max_backlight;
-	}
-	if (drm_dp_dpcd_readb(&intel_dp->aux,
-			      DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max) != 1) {
-		drm_dbg_kms(&i915->drm,
-			    "Failed to read pwmgen bit count cap max\n");
-		return max_backlight;
-	}
-	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
-	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
-
-	/* Ensure frequency is within 25% of desired value */
-	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
-	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
-
-	if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
-		drm_dbg_kms(&i915->drm,
-			    "VBT defined backlight frequency out of range\n");
-		return max_backlight;
-	}
-
-	for (pn = pn_max; pn >= pn_min; pn--) {
-		f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
-		fxp_actual = f << pn;
-		if (fxp_min <= fxp_actual && fxp_actual <= fxp_max)
-			break;
-	}
-
-	drm_dbg_kms(&i915->drm, "Using eDP pwmgen bit count of %d\n", pn);
-	if (drm_dp_dpcd_writeb(&intel_dp->aux,
-			       DP_EDP_PWMGEN_BIT_COUNT, pn) < 0) {
-		drm_dbg_kms(&i915->drm,
-			    "Failed to write aux pwmgen bit count\n");
-		return max_backlight;
-	}
-
-	panel->backlight.edp.vesa.pwmgen_bit_count = pn;
-	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
-		panel->backlight.edp.vesa.pwm_freq_pre_divider = f;
-
-	max_backlight = (1 << pn) - 1;
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
 
-	return max_backlight;
+	drm_edp_backlight_disable(&intel_dp->aux, &panel->backlight.edp.vesa.info);
 }
 
-static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector,
-					     enum pipe pipe)
+static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector, enum pipe pipe)
 {
 	struct intel_panel *panel = &connector->panel;
+	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
+	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+	u16 current_level;
+	u8 current_mode;
+	int ret;
 
-	panel->backlight.max = intel_dp_aux_vesa_calc_max_backlight(connector);
-	if (!panel->backlight.max)
-		return -ENODEV;
+	ret = drm_edp_backlight_init(&intel_dp->aux, &panel->backlight.edp.vesa.info,
+				     i915->vbt.backlight.pwm_freq_hz, intel_dp->edp_dpcd,
+				     &current_level, &current_mode);
+	if (ret < 0)
+		return ret;
 
+	panel->backlight.max = panel->backlight.edp.vesa.info.max;
 	panel->backlight.min = 0;
-	panel->backlight.level = intel_dp_aux_vesa_get_backlight(connector, pipe);
-	panel->backlight.enabled = intel_dp_aux_vesa_backlight_dpcd_mode(connector) &&
-				   panel->backlight.level != 0;
+	if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
+		panel->backlight.level = current_level;
+		panel->backlight.enabled = panel->backlight.level != 0;
+	} else {
+		panel->backlight.level = panel->backlight.max;
+		panel->backlight.enabled = false;
+	}
 
 	return 0;
 }
@@ -558,16 +338,12 @@ intel_dp_aux_supports_vesa_backlight(struct intel_connector *connector)
 	struct intel_dp *intel_dp = intel_attached_dp(connector);
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 
-	/* Check the eDP Display control capabilities registers to determine if
-	 * the panel can support backlight control over the aux channel.
-	 *
-	 * TODO: We currently only support AUX only backlight configurations, not backlights which
+	/* TODO: We currently only support AUX only backlight configurations, not backlights which
 	 * require a mix of PWM and AUX controls to work. In the mean time, these machines typically
 	 * work just fine using normal PWM controls anyway.
 	 */
-	if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
-	    (intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
-	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP)) {
+	if ((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
+	    drm_edp_backlight_supported(intel_dp->edp_dpcd)) {
 		drm_dbg_kms(&i915->drm, "AUX Backlight Control Supported!\n");
 		return true;
 	}
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index edffd1dcca3e..1eca0b42fc45 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1790,6 +1790,24 @@ drm_dp_sink_can_do_video_without_timing_msa(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 		DP_MSA_TIMING_PAR_IGNORED;
 }
 
+/**
+ * drm_edp_backlight_supported() - Check an eDP DPCD for VESA backlight support
+ * @edp_dpcd: The DPCD to check
+ *
+ * Note that currently this function will return %false for panels which support various DPCD
+ * backlight features but which require the brightness be set through PWM, and don't support setting
+ * the brightness level via the DPCD. This is a TODO.
+ *
+ * Returns: %True if @edp_dpcd indicates that VESA backlight controls are supported, %false
+ * otherwise
+ */
+static inline bool
+drm_edp_backlight_supported(const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE])
+{
+	return (edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
+		(edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP);
+}
+
 /*
  * DisplayPort AUX channel
  */
@@ -2089,6 +2107,36 @@ drm_dp_has_quirk(const struct drm_dp_desc *desc, enum drm_dp_quirk quirk)
 	return desc->quirks & BIT(quirk);
 }
 
+/**
+ * struct drm_edp_backlight_info - Probed eDP backlight info struct
+ * @pwmgen_bit_count: The pwmgen bit count
+ * @pwm_freq_pre_divider: The PWM frequency pre-divider value being used for this backlight, if any
+ * @max: The maximum backlight level that may be set
+ * @lsb_reg_used: Do we also write values to the DP_EDP_BACKLIGHT_BRIGHTNESS_LSB register?
+ * @aux_enable: Does the panel support the AUX enable cap?
+ *
+ * This structure contains various data about an eDP backlight, which can be populated by using
+ * drm_edp_backlight_init().
+ */
+struct drm_edp_backlight_info {
+	u8 pwmgen_bit_count;
+	u8 pwm_freq_pre_divider;
+	u16 max;
+
+	bool lsb_reg_used : 1;
+	bool aux_enable : 1;
+};
+
+int
+drm_edp_backlight_init(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl,
+		       u16 driver_pwm_freq_hz, const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE],
+		       u16 *current_level, u8 *current_mode);
+int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
+				u16 level);
+int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
+			     u16 level);
+int drm_edp_backlight_disable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl);
+
 #ifdef CONFIG_DRM_DP_CEC
 void drm_dp_cec_irq(struct drm_dp_aux *aux);
 void drm_dp_cec_register_connector(struct drm_dp_aux *aux,
-- 
2.29.2

Re: [RFC v2 4/5] drm/dp: Extract i915's eDP backlight code into DRM helpers

[Rodrigo Vivi]

On Mon, Jan 25, 2021 at 07:10:30PM -0500, Lyude Paul wrote:
> Since we're about to implement eDP backlight support in nouveau using the
> standard protocol from VESA, we might as well just take the code that's
> already written for this and move it into a set of shared DRM helpers.
> 
> Note that these helpers are intended to handle DPCD related backlight
> control bits such as setting the brightness level over AUX, probing the
> backlight's TCON, enabling/disabling the backlight over AUX if supported,
> etc. Any PWM-related portions of backlight control are explicitly left up
> to the driver, as these will vary from platform to platform.
> 
> The only exception to this is the calculation of the PWM frequency
> pre-divider value. This is because the only platform-specific information
> required for this is the PWM frequency of the panel, which the driver is
> expected to provide if available. The actual algorithm for calculating this
> value is standard and is defined in the eDP specification from VESA.
> 
> Note that these helpers do not yet implement the full range of features
> the VESA backlight interface provides, and only provide the following
> functionality (all of which was already present in i915's DPCD backlight
> support):

This is definitely a good move.

Also the functions are well defined and well documented.

I noticed it wouldn't be straightforward, but I was wondering if it is possible to make the change in 2 steps (at least):
1. modify i915 code in place to match new functions
2. move to drm adding the documentation, proper returns etc....

I couldn't get a good sense of the changes around DPCD mode for instance.

> 
> * Basic control of brightness levels
> * Basic probing of backlight capabilities
> * Helpers for enabling and disabling the backlight
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Dave Airlie <airlied@gmail.com>
> Cc: greg.depoire@gmail.com
> ---
>  drivers/gpu/drm/drm_dp_helper.c               | 332 ++++++++++++++++++
>  .../drm/i915/display/intel_display_types.h    |   3 +-
>  .../drm/i915/display/intel_dp_aux_backlight.c | 288 ++-------------
>  include/drm/drm_dp_helper.h                   |  48 +++
>  4 files changed, 413 insertions(+), 258 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index eedbb48815b7..04cb2b6970a8 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -3082,3 +3082,335 @@ int drm_dp_pcon_convert_rgb_to_ycbcr(struct drm_dp_aux *aux, u8 color_spc)
>  	return 0;
>  }
>  EXPORT_SYMBOL(drm_dp_pcon_convert_rgb_to_ycbcr);
> +
> +/**
> + * drm_edp_backlight_set_level() - Set the backlight level of an eDP panel via AUX
> + * @aux: The DP AUX channel to use
> + * @bl: Backlight capability info from drm_edp_backlight_init()
> + * @level: The brightness level to set
> + *
> + * Sets the brightness level of an eDP panel's backlight. Note that the panel's backlight must
> + * already have been enabled by the driver by calling drm_edp_backlight_enable().
> + *
> + * Returns: %0 on success, negative error code on failure
> + */
> +int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
> +				u16 level)
> +{
> +	int ret;
> +	u8 buf[2] = { 0 };
> +
> +	if (bl->lsb_reg_used) {
> +		buf[0] = (level & 0xFF00) >> 8;
> +		buf[1] = (level & 0x00FF);
> +	} else {
> +		buf[0] = level;
> +	}
> +
> +	ret = drm_dp_dpcd_write(aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB, buf, sizeof(buf));
> +	if (ret != sizeof(buf)) {
> +		DRM_ERROR("%s: Failed to write aux backlight level: %d\n", aux->name, ret);
> +		return ret < 0 ? ret : -EIO;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_edp_backlight_set_level);
> +
> +static int
> +drm_edp_backlight_set_enable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
> +			     bool enable)
> +{
> +	int ret;
> +	u8 buf;
> +
> +	/* The panel uses something other then DPCD for enabling it's backlight */
> +	if (!bl->aux_enable)
> +		return 0;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_DISPLAY_CONTROL_REGISTER, &buf);
> +	if (ret != 1) {
> +		DRM_ERROR("%s: Failed to read eDP display control register: %d\n", aux->name, ret);
> +		return ret < 0 ? ret : -EIO;
> +	}
> +	if (enable)
> +		buf |= DP_EDP_BACKLIGHT_ENABLE;
> +	else
> +		buf &= ~DP_EDP_BACKLIGHT_ENABLE;
> +
> +	ret = drm_dp_dpcd_writeb(aux, DP_EDP_DISPLAY_CONTROL_REGISTER, buf);
> +	if (ret != 1) {
> +		DRM_ERROR("%s: Failed to write eDP display control register: %d\n", aux->name, ret);
> +		return ret < 0 ? ret : -EIO;
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * drm_edp_backlight_enable() - Enable an eDP panel's backlight using DPCD
> + * @aux: The DP AUX channel to use
> + * @bl: Backlight capability info from drm_edp_backlight_init()
> + * @level: The initial backlight level to set via AUX, if there is one
> + *
> + * This function handles enabling DPCD backlight controls on a panel over DPCD, while additionally
> + * restoring any important backlight state such as the given backlight level, the brightness byte
> + * count, backlight frequency, etc.
> + *
> + * Note that certain panels, while supporting brightness level controls over DPCD, may not support
> + * having their backlights enabled via the standard %DP_EDP_DISPLAY_CONTROL_REGISTER. On such panels
> + * &drm_edp_backlight_info.aux_enable will be set to %false, this function will skip the step of
> + * programming the %DP_EDP_DISPLAY_CONTROL_REGISTER, and the driver must perform the required
> + * implementation specific step for enabling the backlight after calling this function.
> + *
> + * Returns: %0 on success, negative error code on failure.
> + */
> +int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
> +			     const u16 level)
> +{
> +	int ret;
> +	u8 dpcd_buf, new_dpcd_buf;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf);
> +	if (ret != 1) {
> +		DRM_DEBUG_KMS("%s: Failed to read backlight mode: %d\n", aux->name, ret);
> +		return ret < 0 ? ret : -EIO;
> +	}
> +
> +	new_dpcd_buf = dpcd_buf;
> +
> +	if ((dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) != DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> +		new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> +		new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> +
> +		ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, bl->pwmgen_bit_count);
> +		if (ret != 1)
> +			DRM_DEBUG_KMS("%s: Failed to write aux pwmgen bit count: %d\n",
> +				      aux->name, ret);
> +	}
> +
> +	if (bl->pwm_freq_pre_divider) {
> +		ret = drm_dp_dpcd_writeb(aux, DP_EDP_BACKLIGHT_FREQ_SET, bl->pwm_freq_pre_divider);
> +		if (ret != 1)
> +			DRM_DEBUG_KMS("%s: Failed to write aux backlight frequency: %d\n",
> +				      aux->name, ret);
> +		else
> +			new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
> +	}
> +
> +	if (new_dpcd_buf != dpcd_buf) {
> +		ret = drm_dp_dpcd_writeb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf);
> +		if (ret != 1) {
> +			DRM_DEBUG_KMS("%s: Failed to write aux backlight mode: %d\n",
> +				      aux->name, ret);
> +			return ret < 0 ? ret : -EIO;
> +		}
> +	}
> +
> +	ret = drm_edp_backlight_set_level(aux, bl, level);
> +	if (ret < 0)
> +		return ret;
> +	ret = drm_edp_backlight_set_enable(aux, bl, true);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_edp_backlight_enable);
> +
> +/**
> + * drm_edp_backlight_disable() - Disable an eDP backlight using DPCD, if supported
> + * @aux: The DP AUX channel to use
> + * @bl: Backlight capability info from drm_edp_backlight_init()
> + *
> + * This function handles disabling DPCD backlight controls on a panel over AUX. Note that some
> + * panels have backlights that are enabled/disabled by other means, despite having their brightness
> + * values controlled through DPCD. On such panels &drm_edp_backlight_info.aux_enable will be set to
> + * %false, this function will become a no-op (and we will skip updating
> + * %DP_EDP_DISPLAY_CONTROL_REGISTER), and the driver must take care to perform it's own
> + * implementation specific step for disabling the backlight.
> + *
> + * Returns: %0 on success or no-op, negative error code on failure.
> + */
> +int drm_edp_backlight_disable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl)
> +{
> +	int ret;
> +
> +	ret = drm_edp_backlight_set_enable(aux, bl, false);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_edp_backlight_disable);
> +
> +static inline int
> +drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl,
> +			    u16 driver_pwm_freq_hz, const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE])
> +{
> +	int fxp, fxp_min, fxp_max, fxp_actual, f = 1;
> +	int ret;
> +	u8 pn, pn_min, pn_max;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT, &pn);
> +	if (ret != 1) {
> +		DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap: %d\n", aux->name, ret);
> +		return -ENODEV;
> +	}
> +
> +	pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> +	bl->max = (1 << pn) - 1;
> +	if (!driver_pwm_freq_hz)
> +		return 0;
> +
> +	/*
> +	 * Set PWM Frequency divider to match desired frequency provided by the driver.
> +	 * The PWM Frequency is calculated as 27Mhz / (F x P).
> +	 * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
> +	 *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
> +	 * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
> +	 *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
> +	 */
> +
> +	/* Find desired value of (F x P)
> +	 * Note that, if F x P is out of supported range, the maximum value or minimum value will
> +	 * applied automatically. So no need to check that.
> +	 */
> +	fxp = DIV_ROUND_CLOSEST(1000 * DP_EDP_BACKLIGHT_FREQ_BASE_KHZ, driver_pwm_freq_hz);
> +
> +	/* Use highest possible value of Pn for more granularity of brightness adjustment while
> +	 * satifying the conditions below.
> +	 * - Pn is in the range of Pn_min and Pn_max
> +	 * - F is in the range of 1 and 255
> +	 * - FxP is within 25% of desired value.
> +	 *   Note: 25% is arbitrary value and may need some tweak.
> +	 */
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min);
> +	if (ret != 1) {
> +		DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap min: %d\n", aux->name, ret);
> +		return 0;
> +	}
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max);
> +	if (ret != 1) {
> +		DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap max: %d\n", aux->name, ret);
> +		return 0;
> +	}
> +	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> +	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> +
> +	/* Ensure frequency is within 25% of desired value */
> +	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
> +	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
> +	if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
> +		DRM_DEBUG_KMS("%s: Driver defined backlight frequency (%d) out of range\n",
> +			      aux->name, driver_pwm_freq_hz);
> +		return 0;
> +	}
> +
> +	for (pn = pn_max; pn >= pn_min; pn--) {
> +		f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
> +		fxp_actual = f << pn;
> +		if (fxp_min <= fxp_actual && fxp_actual <= fxp_max)
> +			break;
> +	}
> +
> +	ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, pn);
> +	if (ret != 1) {
> +		DRM_DEBUG_KMS("%s: Failed to write aux pwmgen bit count: %d\n", aux->name, ret);
> +		return 0;
> +	}
> +	bl->pwmgen_bit_count = pn;
> +	bl->max = (1 << pn) - 1;
> +
> +	if (edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP) {
> +		bl->pwm_freq_pre_divider = f;
> +		DRM_DEBUG_KMS("%s: Using backlight frequency from driver (%dHz)\n",
> +			      aux->name, driver_pwm_freq_hz);
> +	}
> +
> +	return 0;
> +}
> +
> +static inline int
> +drm_edp_backlight_probe_level(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl,
> +			      u8 *current_mode)
> +{
> +	int ret;
> +	u8 buf[2];
> +	u8 mode_reg;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &mode_reg);
> +	if (ret != 1) {
> +		DRM_DEBUG_KMS("%s: Failed to read backlight mode: %d\n", aux->name, ret);
> +		return ret < 0 ? ret : -EIO;
> +	}
> +
> +	*current_mode = (mode_reg & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK);
> +	if (*current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> +		int size = 1 + bl->lsb_reg_used;
> +
> +		ret = drm_dp_dpcd_read(aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB, buf, size);
> +		if (ret != size) {
> +			DRM_DEBUG_KMS("%s: Failed to read backlight level: %d\n", aux->name, ret);
> +			return ret < 0 ? ret : -EIO;
> +		}
> +
> +		if (bl->lsb_reg_used)
> +			return (buf[0] << 8) | buf[1];
> +		else
> +			return buf[0];
> +	}
> +
> +	/*
> +	 * If we're not in DPCD control mode yet, the programmed brightness value is meaningless and
> +	 * the driver should assume max brightness
> +	 */
> +	return bl->max;
> +}
> +
> +/**
> + * drm_edp_backlight_init() - Probe a display panel's TCON using the standard VESA eDP backlight
> + * interface.
> + * @aux: The DP aux device to use for probing
> + * @bl: The &drm_edp_backlight_info struct to fill out with information on the backlight
> + * @driver_pwm_freq_hz: Optional PWM frequency from the driver in hz
> + * @edp_dpcd: A cached copy of the eDP DPCD
> + * @current_level: Where to store the probed brightness level
> + * @current_mode: Where to store the currently set backlight control mode
> + *
> + * Initializes a &drm_edp_backlight_info struct by probing @aux for it's backlight capabilities,
> + * along with also probing the current and maximum supported brightness levels.
> + *
> + * If @driver_pwm_freq_hz is non-zero, this will be used as the backlight frequency. Otherwise, the
> + * default frequency from the panel is used.
> + *
> + * Returns: %0 on success, negative error code on failure.
> + */
> +int
> +drm_edp_backlight_init(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl,
> +		       u16 driver_pwm_freq_hz, const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE],
> +		       u16 *current_level, u8 *current_mode)
> +{
> +	int ret;
> +
> +	if (edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP)
> +		bl->aux_enable = true;
> +	if (edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> +		bl->lsb_reg_used = true;
> +
> +	ret = drm_edp_backlight_probe_max(aux, bl, driver_pwm_freq_hz, edp_dpcd);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = drm_edp_backlight_probe_level(aux, bl, current_mode);
> +	if (ret < 0)
> +		return ret;
> +	*current_level = ret;
> +
> +	DRM_DEBUG_KMS("%s: Found backlight level=%d/%d pwm_freq_pre_divider=%d mode=%x\n",
> +		      aux->name, *current_level, bl->max, bl->pwm_freq_pre_divider, *current_mode);
> +	DRM_DEBUG_KMS("%s: Backlight caps: pwmgen_bit_count=%d lsb_reg_used=%d aux_enable=%d\n",
> +		      aux->name, bl->pwmgen_bit_count, bl->lsb_reg_used, bl->aux_enable);
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_edp_backlight_init);
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index 8450ab8fb245..2af208f1b467 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -263,8 +263,7 @@ struct intel_panel {
>  		/* DPCD backlight */
>  		union {
>  			struct {
> -				u8 pwmgen_bit_count;
> -				u8 pwm_freq_pre_divider;
> +				struct drm_edp_backlight_info info;
>  			} vesa;
>  			struct {
>  				bool sdr_uses_aux;
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> index 62294967f430..1ae14bc9e3fe 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -268,109 +268,19 @@ intel_dp_aux_hdr_setup_backlight(struct intel_connector *connector, enum pipe pi
>  }
>  
>  /* VESA backlight callbacks */
> -static void set_vesa_backlight_enable(struct intel_dp *intel_dp, bool enable)
> -{
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> -	u8 reg_val = 0;
> -
> -	/* Early return when display use other mechanism to enable backlight. */
> -	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP))
> -		return;
> -
> -	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
> -			      &reg_val) < 0) {
> -		drm_dbg_kms(&i915->drm, "Failed to read DPCD register 0x%x\n",
> -			    DP_EDP_DISPLAY_CONTROL_REGISTER);
> -		return;
> -	}
> -	if (enable)
> -		reg_val |= DP_EDP_BACKLIGHT_ENABLE;
> -	else
> -		reg_val &= ~(DP_EDP_BACKLIGHT_ENABLE);
> -
> -	if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
> -			       reg_val) != 1) {
> -		drm_dbg_kms(&i915->drm, "Failed to %s aux backlight\n",
> -			    enable ? "enable" : "disable");
> -	}
> -}
> -
> -static bool intel_dp_aux_vesa_backlight_dpcd_mode(struct intel_connector *connector)
> -{
> -	struct intel_dp *intel_dp = intel_attached_dp(connector);
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> -	u8 mode_reg;
> -
> -	if (drm_dp_dpcd_readb(&intel_dp->aux,
> -			      DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
> -			      &mode_reg) != 1) {
> -		drm_dbg_kms(&i915->drm,
> -			    "Failed to read the DPCD register 0x%x\n",
> -			    DP_EDP_BACKLIGHT_MODE_SET_REGISTER);
> -		return false;
> -	}
> -
> -	return (mode_reg & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) ==
> -	       DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> -}
> -
> -/*
> - * Read the current backlight value from DPCD register(s) based
> - * on if 8-bit(MSB) or 16-bit(MSB and LSB) values are supported
> - */
>  static u32 intel_dp_aux_vesa_get_backlight(struct intel_connector *connector, enum pipe unused)
>  {
> -	struct intel_dp *intel_dp = intel_attached_dp(connector);
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> -	u8 read_val[2] = { 0x0 };
> -	u16 level = 0;
> -
> -	/*
> -	 * If we're not in DPCD control mode yet, the programmed brightness
> -	 * value is meaningless and we should assume max brightness
> -	 */
> -	if (!intel_dp_aux_vesa_backlight_dpcd_mode(connector))
> -		return connector->panel.backlight.max;
> -
> -	if (drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
> -			     &read_val, sizeof(read_val)) < 0) {
> -		drm_dbg_kms(&i915->drm, "Failed to read DPCD register 0x%x\n",
> -			    DP_EDP_BACKLIGHT_BRIGHTNESS_MSB);
> -		return 0;
> -	}
> -	level = read_val[0];
> -	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> -		level = (read_val[0] << 8 | read_val[1]);
> -
> -	return level;
> +	return connector->panel.backlight.level;
>  }
>  
> -/*
> - * Sends the current backlight level over the aux channel, checking if its using
> - * 8-bit or 16 bit value (MSB and LSB)
> - */
>  static void
> -intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state,
> -				u32 level)
> +intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state, u32 level)
>  {
>  	struct intel_connector *connector = to_intel_connector(conn_state->connector);
> -	struct intel_dp *intel_dp = intel_attached_dp(connector);
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> -	u8 vals[2] = { 0x0 };
> -
> -	vals[0] = level;
> +	struct intel_panel *panel = &connector->panel;
> +	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
>  
> -	/* Write the MSB and/or LSB */
> -	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT) {
> -		vals[0] = (level & 0xFF00) >> 8;
> -		vals[1] = (level & 0xFF);
> -	}
> -	if (drm_dp_dpcd_write(&intel_dp->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
> -			      vals, sizeof(vals)) < 0) {
> -		drm_dbg_kms(&i915->drm,
> -			    "Failed to write aux backlight level\n");
> -		return;
> -	}
> +	drm_edp_backlight_set_level(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
>  }
>  
>  static void
> @@ -378,176 +288,46 @@ intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
>  				   const struct drm_connector_state *conn_state, u32 level)
>  {
>  	struct intel_connector *connector = to_intel_connector(conn_state->connector);
> -	struct intel_dp *intel_dp = intel_attached_dp(connector);
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
>  	struct intel_panel *panel = &connector->panel;
> -	u8 dpcd_buf, new_dpcd_buf, edp_backlight_mode;
> -	u8 pwmgen_bit_count = panel->backlight.edp.vesa.pwmgen_bit_count;
> -
> -	if (drm_dp_dpcd_readb(&intel_dp->aux,
> -			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) != 1) {
> -		drm_dbg_kms(&i915->drm, "Failed to read DPCD register 0x%x\n",
> -			    DP_EDP_BACKLIGHT_MODE_SET_REGISTER);
> -		return;
> -	}
> -
> -	new_dpcd_buf = dpcd_buf;
> -	edp_backlight_mode = dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> -
> -	switch (edp_backlight_mode) {
> -	case DP_EDP_BACKLIGHT_CONTROL_MODE_PWM:
> -	case DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET:
> -	case DP_EDP_BACKLIGHT_CONTROL_MODE_PRODUCT:
> -		new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> -		new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> -
> -		if (drm_dp_dpcd_writeb(&intel_dp->aux,
> -				       DP_EDP_PWMGEN_BIT_COUNT,
> -				       pwmgen_bit_count) < 0)
> -			drm_dbg_kms(&i915->drm,
> -				    "Failed to write aux pwmgen bit count\n");
> -
> -		break;
> -
> -	/* Do nothing when it is already DPCD mode */
> -	case DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD:
> -	default:
> -		break;
> -	}
> -
> -	if (panel->backlight.edp.vesa.pwm_freq_pre_divider) {
> -		if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_BACKLIGHT_FREQ_SET,
> -				       panel->backlight.edp.vesa.pwm_freq_pre_divider) == 1)
> -			new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
> -		else
> -			drm_dbg_kms(&i915->drm, "Failed to write aux backlight frequency\n");
> -	}
> -
> -	if (new_dpcd_buf != dpcd_buf) {
> -		if (drm_dp_dpcd_writeb(&intel_dp->aux,
> -			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf) < 0) {
> -			drm_dbg_kms(&i915->drm,
> -				    "Failed to write aux backlight mode\n");
> -		}
> -	}
> +	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
>  
> -	intel_dp_aux_vesa_set_backlight(conn_state, level);
> -	set_vesa_backlight_enable(intel_dp, true);
> +	drm_edp_backlight_enable(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
>  }
>  
>  static void intel_dp_aux_vesa_disable_backlight(const struct drm_connector_state *old_conn_state,
>  						u32 level)
>  {
> -	set_vesa_backlight_enable(enc_to_intel_dp(to_intel_encoder(old_conn_state->best_encoder)),
> -				  false);
> -}
> -
> -/*
> - * Compute PWM frequency divider value based off the frequency provided to us by the vbt.
> - * The PWM Frequency is calculated as 27Mhz / (F x P).
> - * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
> - *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
> - * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
> - *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
> - */
> -static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connector)
> -{
> -	struct drm_i915_private *i915 = to_i915(connector->base.dev);
> -	struct intel_dp *intel_dp = intel_attached_dp(connector);
> +	struct intel_connector *connector = to_intel_connector(old_conn_state->connector);
>  	struct intel_panel *panel = &connector->panel;
> -	u32 max_backlight = 0;
> -	int freq, fxp, fxp_min, fxp_max, fxp_actual, f = 1;
> -	u8 pn, pn_min, pn_max;
> -
> -	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT, &pn) == 1) {
> -		pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> -		max_backlight = (1 << pn) - 1;
> -	}
> -
> -	/* Find desired value of (F x P)
> -	 * Note that, if F x P is out of supported range, the maximum value or
> -	 * minimum value will applied automatically. So no need to check that.
> -	 */
> -	freq = i915->vbt.backlight.pwm_freq_hz;
> -	drm_dbg_kms(&i915->drm, "VBT defined backlight frequency %u Hz\n",
> -		    freq);
> -	if (!freq) {
> -		drm_dbg_kms(&i915->drm,
> -			    "Use panel default backlight frequency\n");
> -		return max_backlight;
> -	}
> -
> -	fxp = DIV_ROUND_CLOSEST(KHz(DP_EDP_BACKLIGHT_FREQ_BASE_KHZ), freq);
> -
> -	/* Use highest possible value of Pn for more granularity of brightness
> -	 * adjustment while satifying the conditions below.
> -	 * - Pn is in the range of Pn_min and Pn_max
> -	 * - F is in the range of 1 and 255
> -	 * - FxP is within 25% of desired value.
> -	 *   Note: 25% is arbitrary value and may need some tweak.
> -	 */
> -	if (drm_dp_dpcd_readb(&intel_dp->aux,
> -			      DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min) != 1) {
> -		drm_dbg_kms(&i915->drm,
> -			    "Failed to read pwmgen bit count cap min\n");
> -		return max_backlight;
> -	}
> -	if (drm_dp_dpcd_readb(&intel_dp->aux,
> -			      DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max) != 1) {
> -		drm_dbg_kms(&i915->drm,
> -			    "Failed to read pwmgen bit count cap max\n");
> -		return max_backlight;
> -	}
> -	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> -	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> -
> -	/* Ensure frequency is within 25% of desired value */
> -	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
> -	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
> -
> -	if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
> -		drm_dbg_kms(&i915->drm,
> -			    "VBT defined backlight frequency out of range\n");
> -		return max_backlight;
> -	}
> -
> -	for (pn = pn_max; pn >= pn_min; pn--) {
> -		f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
> -		fxp_actual = f << pn;
> -		if (fxp_min <= fxp_actual && fxp_actual <= fxp_max)
> -			break;
> -	}
> -
> -	drm_dbg_kms(&i915->drm, "Using eDP pwmgen bit count of %d\n", pn);
> -	if (drm_dp_dpcd_writeb(&intel_dp->aux,
> -			       DP_EDP_PWMGEN_BIT_COUNT, pn) < 0) {
> -		drm_dbg_kms(&i915->drm,
> -			    "Failed to write aux pwmgen bit count\n");
> -		return max_backlight;
> -	}
> -
> -	panel->backlight.edp.vesa.pwmgen_bit_count = pn;
> -	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
> -		panel->backlight.edp.vesa.pwm_freq_pre_divider = f;
> -
> -	max_backlight = (1 << pn) - 1;
> +	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
>  
> -	return max_backlight;
> +	drm_edp_backlight_disable(&intel_dp->aux, &panel->backlight.edp.vesa.info);
>  }
>  
> -static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector,
> -					     enum pipe pipe)
> +static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector, enum pipe pipe)
>  {
>  	struct intel_panel *panel = &connector->panel;
> +	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> +	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> +	u16 current_level;
> +	u8 current_mode;
> +	int ret;
>  
> -	panel->backlight.max = intel_dp_aux_vesa_calc_max_backlight(connector);
> -	if (!panel->backlight.max)
> -		return -ENODEV;
> +	ret = drm_edp_backlight_init(&intel_dp->aux, &panel->backlight.edp.vesa.info,
> +				     i915->vbt.backlight.pwm_freq_hz, intel_dp->edp_dpcd,
> +				     &current_level, &current_mode);
> +	if (ret < 0)
> +		return ret;
>  
> +	panel->backlight.max = panel->backlight.edp.vesa.info.max;
>  	panel->backlight.min = 0;
> -	panel->backlight.level = intel_dp_aux_vesa_get_backlight(connector, pipe);
> -	panel->backlight.enabled = intel_dp_aux_vesa_backlight_dpcd_mode(connector) &&
> -				   panel->backlight.level != 0;
> +	if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> +		panel->backlight.level = current_level;
> +		panel->backlight.enabled = panel->backlight.level != 0;
> +	} else {
> +		panel->backlight.level = panel->backlight.max;
> +		panel->backlight.enabled = false;
> +	}
>  
>  	return 0;
>  }
> @@ -558,16 +338,12 @@ intel_dp_aux_supports_vesa_backlight(struct intel_connector *connector)
>  	struct intel_dp *intel_dp = intel_attached_dp(connector);
>  	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
>  
> -	/* Check the eDP Display control capabilities registers to determine if
> -	 * the panel can support backlight control over the aux channel.
> -	 *
> -	 * TODO: We currently only support AUX only backlight configurations, not backlights which
> +	/* TODO: We currently only support AUX only backlight configurations, not backlights which
>  	 * require a mix of PWM and AUX controls to work. In the mean time, these machines typically
>  	 * work just fine using normal PWM controls anyway.
>  	 */
> -	if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
> -	    (intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
> -	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP)) {
> +	if ((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
> +	    drm_edp_backlight_supported(intel_dp->edp_dpcd)) {
>  		drm_dbg_kms(&i915->drm, "AUX Backlight Control Supported!\n");
>  		return true;
>  	}
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index edffd1dcca3e..1eca0b42fc45 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -1790,6 +1790,24 @@ drm_dp_sink_can_do_video_without_timing_msa(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
>  		DP_MSA_TIMING_PAR_IGNORED;
>  }
>  
> +/**
> + * drm_edp_backlight_supported() - Check an eDP DPCD for VESA backlight support
> + * @edp_dpcd: The DPCD to check
> + *
> + * Note that currently this function will return %false for panels which support various DPCD
> + * backlight features but which require the brightness be set through PWM, and don't support setting
> + * the brightness level via the DPCD. This is a TODO.
> + *
> + * Returns: %True if @edp_dpcd indicates that VESA backlight controls are supported, %false
> + * otherwise
> + */
> +static inline bool
> +drm_edp_backlight_supported(const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE])
> +{
> +	return (edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
> +		(edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP);
> +}
> +
>  /*
>   * DisplayPort AUX channel
>   */
> @@ -2089,6 +2107,36 @@ drm_dp_has_quirk(const struct drm_dp_desc *desc, enum drm_dp_quirk quirk)
>  	return desc->quirks & BIT(quirk);
>  }
>  
> +/**
> + * struct drm_edp_backlight_info - Probed eDP backlight info struct
> + * @pwmgen_bit_count: The pwmgen bit count
> + * @pwm_freq_pre_divider: The PWM frequency pre-divider value being used for this backlight, if any
> + * @max: The maximum backlight level that may be set
> + * @lsb_reg_used: Do we also write values to the DP_EDP_BACKLIGHT_BRIGHTNESS_LSB register?
> + * @aux_enable: Does the panel support the AUX enable cap?
> + *
> + * This structure contains various data about an eDP backlight, which can be populated by using
> + * drm_edp_backlight_init().
> + */
> +struct drm_edp_backlight_info {
> +	u8 pwmgen_bit_count;
> +	u8 pwm_freq_pre_divider;
> +	u16 max;
> +
> +	bool lsb_reg_used : 1;
> +	bool aux_enable : 1;
> +};
> +
> +int
> +drm_edp_backlight_init(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl,
> +		       u16 driver_pwm_freq_hz, const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE],
> +		       u16 *current_level, u8 *current_mode);
> +int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
> +				u16 level);
> +int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
> +			     u16 level);
> +int drm_edp_backlight_disable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl);
> +
>  #ifdef CONFIG_DRM_DP_CEC
>  void drm_dp_cec_irq(struct drm_dp_aux *aux);
>  void drm_dp_cec_register_connector(struct drm_dp_aux *aux,
> -- 
> 2.29.2
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [RFC v2 4/5] drm/dp: Extract i915's eDP backlight code into DRM helpers

[Lyude Paul]

On Wed, 2021-02-03 at 15:58 -0500, Rodrigo Vivi wrote:
> On Mon, Jan 25, 2021 at 07:10:30PM -0500, Lyude Paul wrote:
> > Since we're about to implement eDP backlight support in nouveau using the
> > standard protocol from VESA, we might as well just take the code that's
> > already written for this and move it into a set of shared DRM helpers.
> > 
> > Note that these helpers are intended to handle DPCD related backlight
> > control bits such as setting the brightness level over AUX, probing the
> > backlight's TCON, enabling/disabling the backlight over AUX if supported,
> > etc. Any PWM-related portions of backlight control are explicitly left up
> > to the driver, as these will vary from platform to platform.
> > 
> > The only exception to this is the calculation of the PWM frequency
> > pre-divider value. This is because the only platform-specific information
> > required for this is the PWM frequency of the panel, which the driver is
> > expected to provide if available. The actual algorithm for calculating this
> > value is standard and is defined in the eDP specification from VESA.
> > 
> > Note that these helpers do not yet implement the full range of features
> > the VESA backlight interface provides, and only provide the following
> > functionality (all of which was already present in i915's DPCD backlight
> > support):
> 
> This is definitely a good move.
> 
> Also the functions are well defined and well documented.
> 
> I noticed it wouldn't be straightforward, but I was wondering if it is
> possible to make the change in 2 steps (at least):
> 1. modify i915 code in place to match new functions
> 2. move to drm adding the documentation, proper returns etc....
> 
> I couldn't get a good sense of the changes around DPCD mode for instance.

Good point - yeah I can try to do that ASAP

> 
> > 
> > * Basic control of brightness levels
> > * Basic probing of backlight capabilities
> > * Helpers for enabling and disabling the backlight
> > 
> > Signed-off-by: Lyude Paul <lyude@redhat.com>
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Cc: Dave Airlie <airlied@gmail.com>
> > Cc: greg.depoire@gmail.com
> > ---
> >  drivers/gpu/drm/drm_dp_helper.c               | 332 ++++++++++++++++++
> >  .../drm/i915/display/intel_display_types.h    |   3 +-
> >  .../drm/i915/display/intel_dp_aux_backlight.c | 288 ++-------------
> >  include/drm/drm_dp_helper.h                   |  48 +++
> >  4 files changed, 413 insertions(+), 258 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_dp_helper.c
> > b/drivers/gpu/drm/drm_dp_helper.c
> > index eedbb48815b7..04cb2b6970a8 100644
> > --- a/drivers/gpu/drm/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > @@ -3082,3 +3082,335 @@ int drm_dp_pcon_convert_rgb_to_ycbcr(struct
> > drm_dp_aux *aux, u8 color_spc)
> >         return 0;
> >  }
> >  EXPORT_SYMBOL(drm_dp_pcon_convert_rgb_to_ycbcr);
> > +
> > +/**
> > + * drm_edp_backlight_set_level() - Set the backlight level of an eDP panel
> > via AUX
> > + * @aux: The DP AUX channel to use
> > + * @bl: Backlight capability info from drm_edp_backlight_init()
> > + * @level: The brightness level to set
> > + *
> > + * Sets the brightness level of an eDP panel's backlight. Note that the
> > panel's backlight must
> > + * already have been enabled by the driver by calling
> > drm_edp_backlight_enable().
> > + *
> > + * Returns: %0 on success, negative error code on failure
> > + */
> > +int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl,
> > +                               u16 level)
> > +{
> > +       int ret;
> > +       u8 buf[2] = { 0 };
> > +
> > +       if (bl->lsb_reg_used) {
> > +               buf[0] = (level & 0xFF00) >> 8;
> > +               buf[1] = (level & 0x00FF);
> > +       } else {
> > +               buf[0] = level;
> > +       }
> > +
> > +       ret = drm_dp_dpcd_write(aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB, buf,
> > sizeof(buf));
> > +       if (ret != sizeof(buf)) {
> > +               DRM_ERROR("%s: Failed to write aux backlight level: %d\n",
> > aux->name, ret);
> > +               return ret < 0 ? ret : -EIO;
> > +       }
> > +
> > +       return 0;
> > +}
> > +EXPORT_SYMBOL(drm_edp_backlight_set_level);
> > +
> > +static int
> > +drm_edp_backlight_set_enable(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl,
> > +                            bool enable)
> > +{
> > +       int ret;
> > +       u8 buf;
> > +
> > +       /* The panel uses something other then DPCD for enabling it's
> > backlight */
> > +       if (!bl->aux_enable)
> > +               return 0;
> > +
> > +       ret = drm_dp_dpcd_readb(aux, DP_EDP_DISPLAY_CONTROL_REGISTER, &buf);
> > +       if (ret != 1) {
> > +               DRM_ERROR("%s: Failed to read eDP display control register:
> > %d\n", aux->name, ret);
> > +               return ret < 0 ? ret : -EIO;
> > +       }
> > +       if (enable)
> > +               buf |= DP_EDP_BACKLIGHT_ENABLE;
> > +       else
> > +               buf &= ~DP_EDP_BACKLIGHT_ENABLE;
> > +
> > +       ret = drm_dp_dpcd_writeb(aux, DP_EDP_DISPLAY_CONTROL_REGISTER, buf);
> > +       if (ret != 1) {
> > +               DRM_ERROR("%s: Failed to write eDP display control register:
> > %d\n", aux->name, ret);
> > +               return ret < 0 ? ret : -EIO;
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +/**
> > + * drm_edp_backlight_enable() - Enable an eDP panel's backlight using DPCD
> > + * @aux: The DP AUX channel to use
> > + * @bl: Backlight capability info from drm_edp_backlight_init()
> > + * @level: The initial backlight level to set via AUX, if there is one
> > + *
> > + * This function handles enabling DPCD backlight controls on a panel over
> > DPCD, while additionally
> > + * restoring any important backlight state such as the given backlight
> > level, the brightness byte
> > + * count, backlight frequency, etc.
> > + *
> > + * Note that certain panels, while supporting brightness level controls
> > over DPCD, may not support
> > + * having their backlights enabled via the standard
> > %DP_EDP_DISPLAY_CONTROL_REGISTER. On such panels
> > + * &drm_edp_backlight_info.aux_enable will be set to %false, this function
> > will skip the step of
> > + * programming the %DP_EDP_DISPLAY_CONTROL_REGISTER, and the driver must
> > perform the required
> > + * implementation specific step for enabling the backlight after calling
> > this function.
> > + *
> > + * Returns: %0 on success, negative error code on failure.
> > + */
> > +int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl,
> > +                            const u16 level)
> > +{
> > +       int ret;
> > +       u8 dpcd_buf, new_dpcd_buf;
> > +
> > +       ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
> > &dpcd_buf);
> > +       if (ret != 1) {
> > +               DRM_DEBUG_KMS("%s: Failed to read backlight mode: %d\n",
> > aux->name, ret);
> > +               return ret < 0 ? ret : -EIO;
> > +       }
> > +
> > +       new_dpcd_buf = dpcd_buf;
> > +
> > +       if ((dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) !=
> > DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> > +               new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> > +               new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> > +
> > +               ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, bl-
> > >pwmgen_bit_count);
> > +               if (ret != 1)
> > +                       DRM_DEBUG_KMS("%s: Failed to write aux pwmgen bit
> > count: %d\n",
> > +                                     aux->name, ret);
> > +       }
> > +
> > +       if (bl->pwm_freq_pre_divider) {
> > +               ret = drm_dp_dpcd_writeb(aux, DP_EDP_BACKLIGHT_FREQ_SET, bl-
> > >pwm_freq_pre_divider);
> > +               if (ret != 1)
> > +                       DRM_DEBUG_KMS("%s: Failed to write aux backlight
> > frequency: %d\n",
> > +                                     aux->name, ret);
> > +               else
> > +                       new_dpcd_buf |=
> > DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
> > +       }
> > +
> > +       if (new_dpcd_buf != dpcd_buf) {
> > +               ret = drm_dp_dpcd_writeb(aux,
> > DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf);
> > +               if (ret != 1) {
> > +                       DRM_DEBUG_KMS("%s: Failed to write aux backlight
> > mode: %d\n",
> > +                                     aux->name, ret);
> > +                       return ret < 0 ? ret : -EIO;
> > +               }
> > +       }
> > +
> > +       ret = drm_edp_backlight_set_level(aux, bl, level);
> > +       if (ret < 0)
> > +               return ret;
> > +       ret = drm_edp_backlight_set_enable(aux, bl, true);
> > +       if (ret < 0)
> > +               return ret;
> > +
> > +       return 0;
> > +}
> > +EXPORT_SYMBOL(drm_edp_backlight_enable);
> > +
> > +/**
> > + * drm_edp_backlight_disable() - Disable an eDP backlight using DPCD, if
> > supported
> > + * @aux: The DP AUX channel to use
> > + * @bl: Backlight capability info from drm_edp_backlight_init()
> > + *
> > + * This function handles disabling DPCD backlight controls on a panel over
> > AUX. Note that some
> > + * panels have backlights that are enabled/disabled by other means, despite
> > having their brightness
> > + * values controlled through DPCD. On such panels
> > &drm_edp_backlight_info.aux_enable will be set to
> > + * %false, this function will become a no-op (and we will skip updating
> > + * %DP_EDP_DISPLAY_CONTROL_REGISTER), and the driver must take care to
> > perform it's own
> > + * implementation specific step for disabling the backlight.
> > + *
> > + * Returns: %0 on success or no-op, negative error code on failure.
> > + */
> > +int drm_edp_backlight_disable(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl)
> > +{
> > +       int ret;
> > +
> > +       ret = drm_edp_backlight_set_enable(aux, bl, false);
> > +       if (ret < 0)
> > +               return ret;
> > +
> > +       return 0;
> > +}
> > +EXPORT_SYMBOL(drm_edp_backlight_disable);
> > +
> > +static inline int
> > +drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct
> > drm_edp_backlight_info *bl,
> > +                           u16 driver_pwm_freq_hz, const u8
> > edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE])
> > +{
> > +       int fxp, fxp_min, fxp_max, fxp_actual, f = 1;
> > +       int ret;
> > +       u8 pn, pn_min, pn_max;
> > +
> > +       ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT, &pn);
> > +       if (ret != 1) {
> > +               DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap:
> > %d\n", aux->name, ret);
> > +               return -ENODEV;
> > +       }
> > +
> > +       pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > +       bl->max = (1 << pn) - 1;
> > +       if (!driver_pwm_freq_hz)
> > +               return 0;
> > +
> > +       /*
> > +        * Set PWM Frequency divider to match desired frequency provided by
> > the driver.
> > +        * The PWM Frequency is calculated as 27Mhz / (F x P).
> > +        * - Where F = PWM Frequency Pre-Divider value programmed by field
> > 7:0 of the
> > +        *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
> > +        * - Where P = 2^Pn, where Pn is the value programmed by field 4:0
> > of the
> > +        *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
> > +        */
> > +
> > +       /* Find desired value of (F x P)
> > +        * Note that, if F x P is out of supported range, the maximum value
> > or minimum value will
> > +        * applied automatically. So no need to check that.
> > +        */
> > +       fxp = DIV_ROUND_CLOSEST(1000 * DP_EDP_BACKLIGHT_FREQ_BASE_KHZ,
> > driver_pwm_freq_hz);
> > +
> > +       /* Use highest possible value of Pn for more granularity of
> > brightness adjustment while
> > +        * satifying the conditions below.
> > +        * - Pn is in the range of Pn_min and Pn_max
> > +        * - F is in the range of 1 and 255
> > +        * - FxP is within 25% of desired value.
> > +        *   Note: 25% is arbitrary value and may need some tweak.
> > +        */
> > +       ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN,
> > &pn_min);
> > +       if (ret != 1) {
> > +               DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap min:
> > %d\n", aux->name, ret);
> > +               return 0;
> > +       }
> > +       ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX,
> > &pn_max);
> > +       if (ret != 1) {
> > +               DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap max:
> > %d\n", aux->name, ret);
> > +               return 0;
> > +       }
> > +       pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > +       pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > +
> > +       /* Ensure frequency is within 25% of desired value */
> > +       fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
> > +       fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
> > +       if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
> > +               DRM_DEBUG_KMS("%s: Driver defined backlight frequency (%d)
> > out of range\n",
> > +                             aux->name, driver_pwm_freq_hz);
> > +               return 0;
> > +       }
> > +
> > +       for (pn = pn_max; pn >= pn_min; pn--) {
> > +               f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
> > +               fxp_actual = f << pn;
> > +               if (fxp_min <= fxp_actual && fxp_actual <= fxp_max)
> > +                       break;
> > +       }
> > +
> > +       ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, pn);
> > +       if (ret != 1) {
> > +               DRM_DEBUG_KMS("%s: Failed to write aux pwmgen bit count:
> > %d\n", aux->name, ret);
> > +               return 0;
> > +       }
> > +       bl->pwmgen_bit_count = pn;
> > +       bl->max = (1 << pn) - 1;
> > +
> > +       if (edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP) {
> > +               bl->pwm_freq_pre_divider = f;
> > +               DRM_DEBUG_KMS("%s: Using backlight frequency from driver
> > (%dHz)\n",
> > +                             aux->name, driver_pwm_freq_hz);
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +static inline int
> > +drm_edp_backlight_probe_level(struct drm_dp_aux *aux, struct
> > drm_edp_backlight_info *bl,
> > +                             u8 *current_mode)
> > +{
> > +       int ret;
> > +       u8 buf[2];
> > +       u8 mode_reg;
> > +
> > +       ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
> > &mode_reg);
> > +       if (ret != 1) {
> > +               DRM_DEBUG_KMS("%s: Failed to read backlight mode: %d\n",
> > aux->name, ret);
> > +               return ret < 0 ? ret : -EIO;
> > +       }
> > +
> > +       *current_mode = (mode_reg & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK);
> > +       if (*current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> > +               int size = 1 + bl->lsb_reg_used;
> > +
> > +               ret = drm_dp_dpcd_read(aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
> > buf, size);
> > +               if (ret != size) {
> > +                       DRM_DEBUG_KMS("%s: Failed to read backlight level:
> > %d\n", aux->name, ret);
> > +                       return ret < 0 ? ret : -EIO;
> > +               }
> > +
> > +               if (bl->lsb_reg_used)
> > +                       return (buf[0] << 8) | buf[1];
> > +               else
> > +                       return buf[0];
> > +       }
> > +
> > +       /*
> > +        * If we're not in DPCD control mode yet, the programmed brightness
> > value is meaningless and
> > +        * the driver should assume max brightness
> > +        */
> > +       return bl->max;
> > +}
> > +
> > +/**
> > + * drm_edp_backlight_init() - Probe a display panel's TCON using the
> > standard VESA eDP backlight
> > + * interface.
> > + * @aux: The DP aux device to use for probing
> > + * @bl: The &drm_edp_backlight_info struct to fill out with information on
> > the backlight
> > + * @driver_pwm_freq_hz: Optional PWM frequency from the driver in hz
> > + * @edp_dpcd: A cached copy of the eDP DPCD
> > + * @current_level: Where to store the probed brightness level
> > + * @current_mode: Where to store the currently set backlight control mode
> > + *
> > + * Initializes a &drm_edp_backlight_info struct by probing @aux for it's
> > backlight capabilities,
> > + * along with also probing the current and maximum supported brightness
> > levels.
> > + *
> > + * If @driver_pwm_freq_hz is non-zero, this will be used as the backlight
> > frequency. Otherwise, the
> > + * default frequency from the panel is used.
> > + *
> > + * Returns: %0 on success, negative error code on failure.
> > + */
> > +int
> > +drm_edp_backlight_init(struct drm_dp_aux *aux, struct
> > drm_edp_backlight_info *bl,
> > +                      u16 driver_pwm_freq_hz, const u8
> > edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE],
> > +                      u16 *current_level, u8 *current_mode)
> > +{
> > +       int ret;
> > +
> > +       if (edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP)
> > +               bl->aux_enable = true;
> > +       if (edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> > +               bl->lsb_reg_used = true;
> > +
> > +       ret = drm_edp_backlight_probe_max(aux, bl, driver_pwm_freq_hz,
> > edp_dpcd);
> > +       if (ret < 0)
> > +               return ret;
> > +
> > +       ret = drm_edp_backlight_probe_level(aux, bl, current_mode);
> > +       if (ret < 0)
> > +               return ret;
> > +       *current_level = ret;
> > +
> > +       DRM_DEBUG_KMS("%s: Found backlight level=%d/%d
> > pwm_freq_pre_divider=%d mode=%x\n",
> > +                     aux->name, *current_level, bl->max, bl-
> > >pwm_freq_pre_divider, *current_mode);
> > +       DRM_DEBUG_KMS("%s: Backlight caps: pwmgen_bit_count=%d
> > lsb_reg_used=%d aux_enable=%d\n",
> > +                     aux->name, bl->pwmgen_bit_count, bl->lsb_reg_used, bl-
> > >aux_enable);
> > +       return 0;
> > +}
> > +EXPORT_SYMBOL(drm_edp_backlight_init);
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h
> > b/drivers/gpu/drm/i915/display/intel_display_types.h
> > index 8450ab8fb245..2af208f1b467 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> > @@ -263,8 +263,7 @@ struct intel_panel {
> >                 /* DPCD backlight */
> >                 union {
> >                         struct {
> > -                               u8 pwmgen_bit_count;
> > -                               u8 pwm_freq_pre_divider;
> > +                               struct drm_edp_backlight_info info;
> >                         } vesa;
> >                         struct {
> >                                 bool sdr_uses_aux;
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > index 62294967f430..1ae14bc9e3fe 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > @@ -268,109 +268,19 @@ intel_dp_aux_hdr_setup_backlight(struct
> > intel_connector *connector, enum pipe pi
> >  }
> >  
> >  /* VESA backlight callbacks */
> > -static void set_vesa_backlight_enable(struct intel_dp *intel_dp, bool
> > enable)
> > -{
> > -       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > -       u8 reg_val = 0;
> > -
> > -       /* Early return when display use other mechanism to enable
> > backlight. */
> > -       if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP))
> > -               return;
> > -
> > -       if (drm_dp_dpcd_readb(&intel_dp->aux,
> > DP_EDP_DISPLAY_CONTROL_REGISTER,
> > -                             &reg_val) < 0) {
> > -               drm_dbg_kms(&i915->drm, "Failed to read DPCD register
> > 0x%x\n",
> > -                           DP_EDP_DISPLAY_CONTROL_REGISTER);
> > -               return;
> > -       }
> > -       if (enable)
> > -               reg_val |= DP_EDP_BACKLIGHT_ENABLE;
> > -       else
> > -               reg_val &= ~(DP_EDP_BACKLIGHT_ENABLE);
> > -
> > -       if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > DP_EDP_DISPLAY_CONTROL_REGISTER,
> > -                              reg_val) != 1) {
> > -               drm_dbg_kms(&i915->drm, "Failed to %s aux backlight\n",
> > -                           enable ? "enable" : "disable");
> > -       }
> > -}
> > -
> > -static bool intel_dp_aux_vesa_backlight_dpcd_mode(struct intel_connector
> > *connector)
> > -{
> > -       struct intel_dp *intel_dp = intel_attached_dp(connector);
> > -       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > -       u8 mode_reg;
> > -
> > -       if (drm_dp_dpcd_readb(&intel_dp->aux,
> > -                             DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
> > -                             &mode_reg) != 1) {
> > -               drm_dbg_kms(&i915->drm,
> > -                           "Failed to read the DPCD register 0x%x\n",
> > -                           DP_EDP_BACKLIGHT_MODE_SET_REGISTER);
> > -               return false;
> > -       }
> > -
> > -       return (mode_reg & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) ==
> > -              DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> > -}
> > -
> > -/*
> > - * Read the current backlight value from DPCD register(s) based
> > - * on if 8-bit(MSB) or 16-bit(MSB and LSB) values are supported
> > - */
> >  static u32 intel_dp_aux_vesa_get_backlight(struct intel_connector
> > *connector, enum pipe unused)
> >  {
> > -       struct intel_dp *intel_dp = intel_attached_dp(connector);
> > -       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > -       u8 read_val[2] = { 0x0 };
> > -       u16 level = 0;
> > -
> > -       /*
> > -        * If we're not in DPCD control mode yet, the programmed brightness
> > -        * value is meaningless and we should assume max brightness
> > -        */
> > -       if (!intel_dp_aux_vesa_backlight_dpcd_mode(connector))
> > -               return connector->panel.backlight.max;
> > -
> > -       if (drm_dp_dpcd_read(&intel_dp->aux,
> > DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
> > -                            &read_val, sizeof(read_val)) < 0) {
> > -               drm_dbg_kms(&i915->drm, "Failed to read DPCD register
> > 0x%x\n",
> > -                           DP_EDP_BACKLIGHT_BRIGHTNESS_MSB);
> > -               return 0;
> > -       }
> > -       level = read_val[0];
> > -       if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> > -               level = (read_val[0] << 8 | read_val[1]);
> > -
> > -       return level;
> > +       return connector->panel.backlight.level;
> >  }
> >  
> > -/*
> > - * Sends the current backlight level over the aux channel, checking if its
> > using
> > - * 8-bit or 16 bit value (MSB and LSB)
> > - */
> >  static void
> > -intel_dp_aux_vesa_set_backlight(const struct drm_connector_state
> > *conn_state,
> > -                               u32 level)
> > +intel_dp_aux_vesa_set_backlight(const struct drm_connector_state
> > *conn_state, u32 level)
> >  {
> >         struct intel_connector *connector = to_intel_connector(conn_state-
> > >connector);
> > -       struct intel_dp *intel_dp = intel_attached_dp(connector);
> > -       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > -       u8 vals[2] = { 0x0 };
> > -
> > -       vals[0] = level;
> > +       struct intel_panel *panel = &connector->panel;
> > +       struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> >  
> > -       /* Write the MSB and/or LSB */
> > -       if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> > {
> > -               vals[0] = (level & 0xFF00) >> 8;
> > -               vals[1] = (level & 0xFF);
> > -       }
> > -       if (drm_dp_dpcd_write(&intel_dp->aux,
> > DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
> > -                             vals, sizeof(vals)) < 0) {
> > -               drm_dbg_kms(&i915->drm,
> > -                           "Failed to write aux backlight level\n");
> > -               return;
> > -       }
> > +       drm_edp_backlight_set_level(&intel_dp->aux, &panel-
> > >backlight.edp.vesa.info, level);
> >  }
> >  
> >  static void
> > @@ -378,176 +288,46 @@ intel_dp_aux_vesa_enable_backlight(const struct
> > intel_crtc_state *crtc_state,
> >                                    const struct drm_connector_state
> > *conn_state, u32 level)
> >  {
> >         struct intel_connector *connector = to_intel_connector(conn_state-
> > >connector);
> > -       struct intel_dp *intel_dp = intel_attached_dp(connector);
> > -       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> >         struct intel_panel *panel = &connector->panel;
> > -       u8 dpcd_buf, new_dpcd_buf, edp_backlight_mode;
> > -       u8 pwmgen_bit_count = panel->backlight.edp.vesa.pwmgen_bit_count;
> > -
> > -       if (drm_dp_dpcd_readb(&intel_dp->aux,
> > -                       DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) != 1)
> > {
> > -               drm_dbg_kms(&i915->drm, "Failed to read DPCD register
> > 0x%x\n",
> > -                           DP_EDP_BACKLIGHT_MODE_SET_REGISTER);
> > -               return;
> > -       }
> > -
> > -       new_dpcd_buf = dpcd_buf;
> > -       edp_backlight_mode = dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> > -
> > -       switch (edp_backlight_mode) {
> > -       case DP_EDP_BACKLIGHT_CONTROL_MODE_PWM:
> > -       case DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET:
> > -       case DP_EDP_BACKLIGHT_CONTROL_MODE_PRODUCT:
> > -               new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> > -               new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> > -
> > -               if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > -                                      DP_EDP_PWMGEN_BIT_COUNT,
> > -                                      pwmgen_bit_count) < 0)
> > -                       drm_dbg_kms(&i915->drm,
> > -                                   "Failed to write aux pwmgen bit
> > count\n");
> > -
> > -               break;
> > -
> > -       /* Do nothing when it is already DPCD mode */
> > -       case DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD:
> > -       default:
> > -               break;
> > -       }
> > -
> > -       if (panel->backlight.edp.vesa.pwm_freq_pre_divider) {
> > -               if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > DP_EDP_BACKLIGHT_FREQ_SET,
> > -                                      panel-
> > >backlight.edp.vesa.pwm_freq_pre_divider) == 1)
> > -                       new_dpcd_buf |=
> > DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
> > -               else
> > -                       drm_dbg_kms(&i915->drm, "Failed to write aux
> > backlight frequency\n");
> > -       }
> > -
> > -       if (new_dpcd_buf != dpcd_buf) {
> > -               if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > -                       DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf) <
> > 0) {
> > -                       drm_dbg_kms(&i915->drm,
> > -                                   "Failed to write aux backlight mode\n");
> > -               }
> > -       }
> > +       struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> >  
> > -       intel_dp_aux_vesa_set_backlight(conn_state, level);
> > -       set_vesa_backlight_enable(intel_dp, true);
> > +       drm_edp_backlight_enable(&intel_dp->aux, &panel-
> > >backlight.edp.vesa.info, level);
> >  }
> >  
> >  static void intel_dp_aux_vesa_disable_backlight(const struct
> > drm_connector_state *old_conn_state,
> >                                                 u32 level)
> >  {
> > -
> >        set_vesa_backlight_enable(enc_to_intel_dp(to_intel_encoder(old_conn_st
> > ate->best_encoder)),
> > -                                 false);
> > -}
> > -
> > -/*
> > - * Compute PWM frequency divider value based off the frequency provided to
> > us by the vbt.
> > - * The PWM Frequency is calculated as 27Mhz / (F x P).
> > - * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of
> > the
> > - *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
> > - * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
> > - *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
> > - */
> > -static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector
> > *connector)
> > -{
> > -       struct drm_i915_private *i915 = to_i915(connector->base.dev);
> > -       struct intel_dp *intel_dp = intel_attached_dp(connector);
> > +       struct intel_connector *connector =
> > to_intel_connector(old_conn_state->connector);
> >         struct intel_panel *panel = &connector->panel;
> > -       u32 max_backlight = 0;
> > -       int freq, fxp, fxp_min, fxp_max, fxp_actual, f = 1;
> > -       u8 pn, pn_min, pn_max;
> > -
> > -       if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT, &pn)
> > == 1) {
> > -               pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > -               max_backlight = (1 << pn) - 1;
> > -       }
> > -
> > -       /* Find desired value of (F x P)
> > -        * Note that, if F x P is out of supported range, the maximum value
> > or
> > -        * minimum value will applied automatically. So no need to check
> > that.
> > -        */
> > -       freq = i915->vbt.backlight.pwm_freq_hz;
> > -       drm_dbg_kms(&i915->drm, "VBT defined backlight frequency %u Hz\n",
> > -                   freq);
> > -       if (!freq) {
> > -               drm_dbg_kms(&i915->drm,
> > -                           "Use panel default backlight frequency\n");
> > -               return max_backlight;
> > -       }
> > -
> > -       fxp = DIV_ROUND_CLOSEST(KHz(DP_EDP_BACKLIGHT_FREQ_BASE_KHZ), freq);
> > -
> > -       /* Use highest possible value of Pn for more granularity of
> > brightness
> > -        * adjustment while satifying the conditions below.
> > -        * - Pn is in the range of Pn_min and Pn_max
> > -        * - F is in the range of 1 and 255
> > -        * - FxP is within 25% of desired value.
> > -        *   Note: 25% is arbitrary value and may need some tweak.
> > -        */
> > -       if (drm_dp_dpcd_readb(&intel_dp->aux,
> > -                             DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min) !=
> > 1) {
> > -               drm_dbg_kms(&i915->drm,
> > -                           "Failed to read pwmgen bit count cap min\n");
> > -               return max_backlight;
> > -       }
> > -       if (drm_dp_dpcd_readb(&intel_dp->aux,
> > -                             DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max) !=
> > 1) {
> > -               drm_dbg_kms(&i915->drm,
> > -                           "Failed to read pwmgen bit count cap max\n");
> > -               return max_backlight;
> > -       }
> > -       pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > -       pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > -
> > -       /* Ensure frequency is within 25% of desired value */
> > -       fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
> > -       fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
> > -
> > -       if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
> > -               drm_dbg_kms(&i915->drm,
> > -                           "VBT defined backlight frequency out of
> > range\n");
> > -               return max_backlight;
> > -       }
> > -
> > -       for (pn = pn_max; pn >= pn_min; pn--) {
> > -               f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
> > -               fxp_actual = f << pn;
> > -               if (fxp_min <= fxp_actual && fxp_actual <= fxp_max)
> > -                       break;
> > -       }
> > -
> > -       drm_dbg_kms(&i915->drm, "Using eDP pwmgen bit count of %d\n", pn);
> > -       if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > -                              DP_EDP_PWMGEN_BIT_COUNT, pn) < 0) {
> > -               drm_dbg_kms(&i915->drm,
> > -                           "Failed to write aux pwmgen bit count\n");
> > -               return max_backlight;
> > -       }
> > -
> > -       panel->backlight.edp.vesa.pwmgen_bit_count = pn;
> > -       if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
> > -               panel->backlight.edp.vesa.pwm_freq_pre_divider = f;
> > -
> > -       max_backlight = (1 << pn) - 1;
> > +       struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> >  
> > -       return max_backlight;
> > +       drm_edp_backlight_disable(&intel_dp->aux, &panel-
> > >backlight.edp.vesa.info);
> >  }
> >  
> > -static int intel_dp_aux_vesa_setup_backlight(struct intel_connector
> > *connector,
> > -                                            enum pipe pipe)
> > +static int intel_dp_aux_vesa_setup_backlight(struct intel_connector
> > *connector, enum pipe pipe)
> >  {
> >         struct intel_panel *panel = &connector->panel;
> > +       struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> > +       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > +       u16 current_level;
> > +       u8 current_mode;
> > +       int ret;
> >  
> > -       panel->backlight.max =
> > intel_dp_aux_vesa_calc_max_backlight(connector);
> > -       if (!panel->backlight.max)
> > -               return -ENODEV;
> > +       ret = drm_edp_backlight_init(&intel_dp->aux, &panel-
> > >backlight.edp.vesa.info,
> > +                                    i915->vbt.backlight.pwm_freq_hz,
> > intel_dp->edp_dpcd,
> > +                                    &current_level, &current_mode);
> > +       if (ret < 0)
> > +               return ret;
> >  
> > +       panel->backlight.max = panel->backlight.edp.vesa.info.max;
> >         panel->backlight.min = 0;
> > -       panel->backlight.level = intel_dp_aux_vesa_get_backlight(connector,
> > pipe);
> > -       panel->backlight.enabled =
> > intel_dp_aux_vesa_backlight_dpcd_mode(connector) &&
> > -                                  panel->backlight.level != 0;
> > +       if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> > +               panel->backlight.level = current_level;
> > +               panel->backlight.enabled = panel->backlight.level != 0;
> > +       } else {
> > +               panel->backlight.level = panel->backlight.max;
> > +               panel->backlight.enabled = false;
> > +       }
> >  
> >         return 0;
> >  }
> > @@ -558,16 +338,12 @@ intel_dp_aux_supports_vesa_backlight(struct
> > intel_connector *connector)
> >         struct intel_dp *intel_dp = intel_attached_dp(connector);
> >         struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> >  
> > -       /* Check the eDP Display control capabilities registers to determine
> > if
> > -        * the panel can support backlight control over the aux channel.
> > -        *
> > -        * TODO: We currently only support AUX only backlight
> > configurations, not backlights which
> > +       /* TODO: We currently only support AUX only backlight
> > configurations, not backlights which
> >          * require a mix of PWM and AUX controls to work. In the mean time,
> > these machines typically
> >          * work just fine using normal PWM controls anyway.
> >          */
> > -       if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
> > -           (intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
> > -           (intel_dp->edp_dpcd[2] &
> > DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP)) {
> > +       if ((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
> > +           drm_edp_backlight_supported(intel_dp->edp_dpcd)) {
> >                 drm_dbg_kms(&i915->drm, "AUX Backlight Control
> > Supported!\n");
> >                 return true;
> >         }
> > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> > index edffd1dcca3e..1eca0b42fc45 100644
> > --- a/include/drm/drm_dp_helper.h
> > +++ b/include/drm/drm_dp_helper.h
> > @@ -1790,6 +1790,24 @@ drm_dp_sink_can_do_video_without_timing_msa(const u8
> > dpcd[DP_RECEIVER_CAP_SIZE])
> >                 DP_MSA_TIMING_PAR_IGNORED;
> >  }
> >  
> > +/**
> > + * drm_edp_backlight_supported() - Check an eDP DPCD for VESA backlight
> > support
> > + * @edp_dpcd: The DPCD to check
> > + *
> > + * Note that currently this function will return %false for panels which
> > support various DPCD
> > + * backlight features but which require the brightness be set through PWM,
> > and don't support setting
> > + * the brightness level via the DPCD. This is a TODO.
> > + *
> > + * Returns: %True if @edp_dpcd indicates that VESA backlight controls are
> > supported, %false
> > + * otherwise
> > + */
> > +static inline bool
> > +drm_edp_backlight_supported(const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE])
> > +{
> > +       return (edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
> > +               (edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP);
> > +}
> > +
> >  /*
> >   * DisplayPort AUX channel
> >   */
> > @@ -2089,6 +2107,36 @@ drm_dp_has_quirk(const struct drm_dp_desc *desc, enum
> > drm_dp_quirk quirk)
> >         return desc->quirks & BIT(quirk);
> >  }
> >  
> > +/**
> > + * struct drm_edp_backlight_info - Probed eDP backlight info struct
> > + * @pwmgen_bit_count: The pwmgen bit count
> > + * @pwm_freq_pre_divider: The PWM frequency pre-divider value being used
> > for this backlight, if any
> > + * @max: The maximum backlight level that may be set
> > + * @lsb_reg_used: Do we also write values to the
> > DP_EDP_BACKLIGHT_BRIGHTNESS_LSB register?
> > + * @aux_enable: Does the panel support the AUX enable cap?
> > + *
> > + * This structure contains various data about an eDP backlight, which can
> > be populated by using
> > + * drm_edp_backlight_init().
> > + */
> > +struct drm_edp_backlight_info {
> > +       u8 pwmgen_bit_count;
> > +       u8 pwm_freq_pre_divider;
> > +       u16 max;
> > +
> > +       bool lsb_reg_used : 1;
> > +       bool aux_enable : 1;
> > +};
> > +
> > +int
> > +drm_edp_backlight_init(struct drm_dp_aux *aux, struct
> > drm_edp_backlight_info *bl,
> > +                      u16 driver_pwm_freq_hz, const u8
> > edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE],
> > +                      u16 *current_level, u8 *current_mode);
> > +int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl,
> > +                               u16 level);
> > +int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl,
> > +                            u16 level);
> > +int drm_edp_backlight_disable(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl);
> > +
> >  #ifdef CONFIG_DRM_DP_CEC
> >  void drm_dp_cec_irq(struct drm_dp_aux *aux);
> >  void drm_dp_cec_register_connector(struct drm_dp_aux *aux,
> > -- 
> > 2.29.2
> > 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 

-- 
Sincerely,
   Lyude Paul (she/her)
   Software Engineer at Red Hat
   
Note: I deal with a lot of emails and have a lot of bugs on my plate. If you've
asked me a question, are waiting for a review/merge on a patch, etc. and I
haven't responded in a while, please feel free to send me another email to check
on my status. I don't bite!

[RFC v2 5/5] drm/nouveau/kms/nv50-: Add basic DPCD backlight support for nouveau

[Lyude Paul]

This adds support for controlling panel backlights over eDP using VESA's
standard backlight control interface. Luckily, Nvidia was cool enough to
never come up with their own proprietary backlight control interface (at
least, not any that I or the laptop manufacturers I've talked to are aware
of), so this should work for any laptop panels which support the VESA
backlight control interface.

Note that we don't yet provide the panel backlight frequency to the DRM DP
backlight helpers. This should be fine for the time being, since it's not
required to get basic backlight controls working.

For reference: there's some mentions of PWM backlight values in
nouveau_reg.h, but I'm not sure these are the values we would want to use.
If we figure out how to get this information in the future, we'll have the
benefit of more granular backlight control.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: greg.depoire@gmail.com
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c     |  30 +++-
 drivers/gpu/drm/nouveau/nouveau_backlight.c | 166 ++++++++++++++++++--
 drivers/gpu/drm/nouveau/nouveau_connector.h |   9 +-
 drivers/gpu/drm/nouveau/nouveau_encoder.h   |   1 +
 4 files changed, 187 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index c6367035970e..70dc1a79a3f0 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -31,6 +31,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/hdmi.h>
 #include <linux/component.h>
+#include <linux/iopoll.h>
 
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
@@ -1615,23 +1616,38 @@ nv50_sor_update(struct nouveau_encoder *nv_encoder, u8 head,
 	core->func->sor->ctrl(core, nv_encoder->or, nv_encoder->ctrl, asyh);
 }
 
+/* TODO: Should we extend this to PWM-only backlights?
+ * As well, should we add a DRM helper for waiting for the backlight to acknowledge
+ * the panel backlight has been shut off? Intel doesn't seem to do this, and uses a
+ * fixed time delay from the vbios…
+ */
 static void
 nv50_sor_disable(struct drm_encoder *encoder,
 		 struct drm_atomic_state *state)
 {
 	struct nouveau_encoder *nv_encoder = nouveau_encoder(encoder);
+	struct nouveau_drm *drm = nouveau_drm(nv_encoder->base.base.dev);
 	struct nouveau_crtc *nv_crtc = nouveau_crtc(nv_encoder->crtc);
 	struct nouveau_connector *nv_connector =
 		nv50_outp_get_old_connector(nv_encoder, state);
+	int ret;
 
 	nv_encoder->crtc = NULL;
 
 	if (nv_crtc) {
 		struct drm_dp_aux *aux = &nv_connector->aux;
+		struct nouveau_backlight *backlight = nv_connector->backlight;
 		u8 pwr;
 
+		if (backlight && backlight->uses_dpcd) {
+			ret = drm_edp_backlight_disable(aux, &backlight->edp_info);
+			if (ret < 0)
+				NV_ERROR(drm, "Failed to disable backlight on [CONNECTOR:%d:%s]: %d\n",
+					 nv_connector->base.base.id, nv_connector->base.name, ret);
+		}
+
 		if (nv_encoder->dcb->type == DCB_OUTPUT_DP) {
-			int ret = drm_dp_dpcd_readb(aux, DP_SET_POWER, &pwr);
+			ret = drm_dp_dpcd_readb(aux, DP_SET_POWER, &pwr);
 
 			if (ret == 0) {
 				pwr &= ~DP_SET_POWER_MASK;
@@ -1667,6 +1683,9 @@ nv50_sor_enable(struct drm_encoder *encoder, struct drm_atomic_state *state)
 	struct drm_device *dev = encoder->dev;
 	struct nouveau_drm *drm = nouveau_drm(dev);
 	struct nouveau_connector *nv_connector;
+#ifdef CONFIG_DRM_NOUVEAU_BACKLIGHT
+	struct nouveau_backlight *backlight;
+#endif
 	struct nvbios *bios = &drm->vbios;
 	bool hda = false;
 	u8 proto = NV507D_SOR_SET_CONTROL_PROTOCOL_CUSTOM;
@@ -1741,6 +1760,14 @@ nv50_sor_enable(struct drm_encoder *encoder, struct drm_atomic_state *state)
 			proto = NV887D_SOR_SET_CONTROL_PROTOCOL_DP_B;
 
 		nv50_audio_enable(encoder, state, mode);
+
+#ifdef CONFIG_DRM_NOUVEAU_BACKLIGHT
+		backlight = nv_connector->backlight;
+		if (backlight && backlight->uses_dpcd)
+			drm_edp_backlight_enable(&nv_connector->aux, &backlight->edp_info,
+						 (u16)backlight->dev->props.brightness);
+#endif
+
 		break;
 	default:
 		BUG();
@@ -2263,6 +2290,7 @@ nv50_disp_atomic_commit_tail(struct drm_atomic_state *state)
 	nv50_crc_atomic_start_reporting(state);
 	if (!flushed)
 		nv50_crc_atomic_release_notifier_contexts(state);
+
 	drm_atomic_helper_commit_hw_done(state);
 	drm_atomic_helper_cleanup_planes(dev, state);
 	drm_atomic_helper_commit_cleanup_done(state);
diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c b/drivers/gpu/drm/nouveau/nouveau_backlight.c
index 42b498e7e2bf..a11811b5e63e 100644
--- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
+++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c
@@ -42,11 +42,6 @@
 static struct ida bl_ida;
 #define BL_NAME_SIZE 15 // 12 for name + 2 for digits + 1 for '\0'
 
-struct nouveau_backlight {
-	struct backlight_device *dev;
-	int id;
-};
-
 static bool
 nouveau_get_backlight_name(char backlight_name[BL_NAME_SIZE],
 			   struct nouveau_backlight *bl)
@@ -147,6 +142,98 @@ static const struct backlight_ops nv50_bl_ops = {
 	.update_status = nv50_set_intensity,
 };
 
+/*
+ * eDP brightness callbacks need to happen under lock, since we need to
+ * enable/disable the backlight ourselves for modesets
+ */
+static int
+nv50_edp_get_brightness(struct backlight_device *bd)
+{
+	struct drm_connector *connector = dev_get_drvdata(bd->dev.parent);
+	struct drm_device *dev = connector->dev;
+	struct drm_crtc *crtc;
+	struct drm_modeset_acquire_ctx ctx;
+	int ret = 0;
+
+	drm_modeset_acquire_init(&ctx, 0);
+
+retry:
+	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, &ctx);
+	if (ret == -EDEADLK)
+		goto deadlock;
+	else if (ret < 0)
+		goto out;
+
+	crtc = connector->state->crtc;
+	if (!crtc)
+		goto out;
+
+	ret = drm_modeset_lock(&crtc->mutex, &ctx);
+	if (ret == -EDEADLK)
+		goto deadlock;
+	else if (ret < 0)
+		goto out;
+
+	if (!crtc->state->active)
+		goto out;
+
+	ret = bd->props.brightness;
+out:
+	drm_modeset_drop_locks(&ctx);
+	drm_modeset_acquire_fini(&ctx);
+	return ret;
+deadlock:
+	drm_modeset_backoff(&ctx);
+	goto retry;
+}
+
+static int
+nv50_edp_set_brightness(struct backlight_device *bd)
+{
+	struct drm_connector *connector = dev_get_drvdata(bd->dev.parent);
+	struct nouveau_connector *nv_connector = nouveau_connector(connector);
+	struct drm_device *dev = connector->dev;
+	struct drm_crtc *crtc;
+	struct drm_dp_aux *aux = &nv_connector->aux;
+	struct nouveau_backlight *nv_bl = nv_connector->backlight;
+	struct drm_modeset_acquire_ctx ctx;
+	int ret = 0;
+
+	drm_modeset_acquire_init(&ctx, 0);
+retry:
+	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, &ctx);
+	if (ret == -EDEADLK)
+		goto deadlock;
+	else if (ret < 0)
+		goto out;
+
+	crtc = connector->state->crtc;
+	if (!crtc)
+		goto out;
+
+	ret = drm_modeset_lock(&crtc->mutex, &ctx);
+	if (ret == -EDEADLK)
+		goto deadlock;
+	else if (ret < 0)
+		goto out;
+
+	if (crtc->state->active)
+		ret = drm_edp_backlight_set_level(aux, &nv_bl->edp_info, bd->props.brightness);
+
+out:
+	drm_modeset_drop_locks(&ctx);
+	drm_modeset_acquire_fini(&ctx);
+	return ret;
+deadlock:
+	drm_modeset_backoff(&ctx);
+	goto retry;
+}
+
+static const struct backlight_ops nv50_edp_bl_ops = {
+	.get_brightness = nv50_edp_get_brightness,
+	.update_status = nv50_edp_set_brightness,
+};
+
 static int
 nva3_get_intensity(struct backlight_device *bd)
 {
@@ -193,8 +280,13 @@ static const struct backlight_ops nva3_bl_ops = {
 	.update_status = nva3_set_intensity,
 };
 
+/* FIXME: perform backlight probing for eDP _before_ this, this only gets called after connector
+ * registration which happens after the initial modeset
+ */
 static int
-nv50_backlight_init(struct nouveau_encoder *nv_encoder,
+nv50_backlight_init(struct nouveau_backlight *bl,
+		    struct nouveau_connector *nv_conn,
+		    struct nouveau_encoder *nv_encoder,
 		    struct backlight_properties *props,
 		    const struct backlight_ops **ops)
 {
@@ -204,6 +296,41 @@ nv50_backlight_init(struct nouveau_encoder *nv_encoder,
 	if (!nvif_rd32(device, NV50_PDISP_SOR_PWM_CTL(ffs(nv_encoder->dcb->or) - 1)))
 		return -ENODEV;
 
+	if (nv_conn->type == DCB_CONNECTOR_eDP) {
+		int ret;
+		u16 current_level;
+		u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE];
+		u8 current_mode;
+
+		ret = drm_dp_dpcd_read(&nv_conn->aux, DP_EDP_DPCD_REV, edp_dpcd,
+				       EDP_DISPLAY_CTL_CAP_SIZE);
+		if (ret < 0)
+			return ret;
+
+		if (drm_edp_backlight_supported(edp_dpcd)) {
+			NV_DEBUG(drm, "DPCD backlight controls supported on %s\n",
+				 nv_conn->base.name);
+
+			ret = drm_edp_backlight_init(&nv_conn->aux, &bl->edp_info, 0, edp_dpcd,
+						     &current_level, &current_mode);
+			if (ret < 0)
+				return ret;
+
+			ret = drm_edp_backlight_enable(&nv_conn->aux, &bl->edp_info, current_level);
+			if (ret < 0) {
+				NV_ERROR(drm, "Failed to enable backlight on %s: %d\n",
+					 nv_conn->base.name, ret);
+				return ret;
+			}
+
+			*ops = &nv50_edp_bl_ops;
+			props->brightness = current_level;
+			props->max_brightness = bl->edp_info.max;
+			bl->uses_dpcd = true;
+			return 0;
+		}
+	}
+
 	if (drm->client.device.info.chipset <= 0xa0 ||
 	    drm->client.device.info.chipset == 0xaa ||
 	    drm->client.device.info.chipset == 0xac)
@@ -243,6 +370,10 @@ nouveau_backlight_init(struct drm_connector *connector)
 	if (!nv_encoder)
 		return 0;
 
+	bl = kzalloc(sizeof(*bl), GFP_KERNEL);
+	if (!bl)
+		return -ENOMEM;
+
 	switch (device->info.family) {
 	case NV_DEVICE_INFO_V0_CURIE:
 		ret = nv40_backlight_init(nv_encoder, &props, &ops);
@@ -255,20 +386,19 @@ nouveau_backlight_init(struct drm_connector *connector)
 	case NV_DEVICE_INFO_V0_VOLTA:
 	case NV_DEVICE_INFO_V0_TURING:
 	case NV_DEVICE_INFO_V0_AMPERE: //XXX: not confirmed
-		ret = nv50_backlight_init(nv_encoder, &props, &ops);
+		ret = nv50_backlight_init(bl, nouveau_connector(connector),
+					  nv_encoder, &props, &ops);
 		break;
 	default:
-		return 0;
+		ret = 0;
+		goto fail_alloc;
 	}
 
-	if (ret == -ENODEV)
-		return 0;
-	else if (ret)
-		return ret;
-
-	bl = kzalloc(sizeof(*bl), GFP_KERNEL);
-	if (!bl)
-		return -ENOMEM;
+	if (ret) {
+		if (ret == -ENODEV)
+			ret = 0;
+		goto fail_alloc;
+	}
 
 	if (!nouveau_get_backlight_name(backlight_name, bl)) {
 		NV_ERROR(drm, "Failed to retrieve a unique name for the backlight interface\n");
@@ -285,7 +415,9 @@ nouveau_backlight_init(struct drm_connector *connector)
 	}
 
 	nouveau_connector(connector)->backlight = bl;
-	bl->dev->props.brightness = bl->dev->ops->get_brightness(bl->dev);
+	if (!bl->dev->props.brightness)
+		bl->dev->props.brightness =
+			bl->dev->ops->get_brightness(bl->dev);
 	backlight_update_status(bl->dev);
 
 	return 0;
diff --git a/drivers/gpu/drm/nouveau/nouveau_connector.h b/drivers/gpu/drm/nouveau/nouveau_connector.h
index d0b859c4a80e..40f90e353540 100644
--- a/drivers/gpu/drm/nouveau/nouveau_connector.h
+++ b/drivers/gpu/drm/nouveau/nouveau_connector.h
@@ -46,7 +46,14 @@ struct nvkm_i2c_port;
 struct dcb_output;
 
 #ifdef CONFIG_DRM_NOUVEAU_BACKLIGHT
-struct nouveau_backlight;
+struct nouveau_backlight {
+	struct backlight_device *dev;
+
+	struct drm_edp_backlight_info edp_info;
+	bool uses_dpcd : 1;
+
+	int id;
+};
 #endif
 
 #define nouveau_conn_atom(p)                                                   \
diff --git a/drivers/gpu/drm/nouveau/nouveau_encoder.h b/drivers/gpu/drm/nouveau/nouveau_encoder.h
index 21937f1c7dd9..8be4b014b471 100644
--- a/drivers/gpu/drm/nouveau/nouveau_encoder.h
+++ b/drivers/gpu/drm/nouveau/nouveau_encoder.h
@@ -30,6 +30,7 @@
 #include <subdev/bios/dcb.h>
 
 #include <drm/drm_encoder_slave.h>
+#include <drm/drm_dp_helper.h>
 #include <drm/drm_dp_mst_helper.h>
 #include "dispnv04/disp.h"
 struct nv50_head_atom;
-- 
2.29.2