[PATCH v2 0/6] drm/panel: atna33xc20: Fix the Samsung ATNA33XC20 panel

[PATCH v2 0/6] drm/panel: atna33xc20: Fix the Samsung ATNA33XC20 panel

[Douglas Anderson]

The overall goal of this series is to make the Samsung ATNA33XC20
panel work more properly. As part of this, we have:
* A bugfix for the recently abstracted DP AUX backlight code.
* A bugfix for the sequencing of the ti-sn65dsi86 bridge driver.
* Removal of the panel from panel-simple and moving it to its own
  driver.

If the bugfixes look good but the rest of the series needs work then
those could land early on their own. There's no real compile time
dependency on the bugfixes, things are just glitchier without them.

NOTE: this series will (slightly) conflict with my other recent series
making eDP panels probable [1]. I'll re-post that one atop this
one. It should be noted that the fact that the Samsung ATNA33XC20
needs its own panel driver means that it _can't_ handled as a probed
driver. I think this is fine, at least for now. I don't think it would
be easy to make a unified design with this panel and other panels
given that it's an AMOLED panel and has a whole bunch of different
components on board.

As discussed in IRC, the only difference in v2 is the addition of a
"Fixes" tag to patch #3 and the collection of Reviews/Acks from Sean
and Robert.

If people feel that this is ready to land today then I can help land
it (please let me know). Otherwise I'm happy for someone else to
actually do the commit next week (I'm on vacation) or I can take it
when I get back.

[1] https://lore.kernel.org/r/20210723002146.1962910-1-dianders@chromium.org/

Changes in v2:
- Added Fixes tag as requested by Sam.

Douglas Anderson (6):
  drm/dp: Don't zero PWMGEN_BIT_COUNT when driver_pwm_freq_hz not
    specified
  drm/bridge: ti-sn65dsi86: Fix power off sequence
  drm/bridge: ti-sn65dsi86: Add some 100 us delays
  Revert "drm/panel-simple: Add Samsung ATNA33XC20"
  Revert "drm/panel-simple: Support for delays between GPIO & regulator"
  drm/panel: atna33xc20: Introduce the Samsung ATNA33XC20 panel

 drivers/gpu/drm/bridge/ti-sn65dsi86.c         |  17 +-
 drivers/gpu/drm/drm_dp_helper.c               |  10 +-
 drivers/gpu/drm/panel/Kconfig                 |  12 +
 drivers/gpu/drm/panel/Makefile                |   1 +
 .../gpu/drm/panel/panel-samsung-atna33xc20.c  | 366 ++++++++++++++++++
 drivers/gpu/drm/panel/panel-simple.c          |  61 ---
 6 files changed, 398 insertions(+), 69 deletions(-)
 create mode 100644 drivers/gpu/drm/panel/panel-samsung-atna33xc20.c

-- 
2.32.0.554.ge1b32706d8-goog

[PATCH v2 1/6] drm/dp: Don't zero PWMGEN_BIT_COUNT when driver_pwm_freq_hz not specified

[Douglas Anderson]

The function drm_edp_backlight_init() is defined such that the
"driver_pwm_freq_hz" parameter is optional--it's 0 if you don't want
to futz with it. If you follow this variable through, you'll find out
that if it's 0 we won't ever set the "bl->pwmgen_bit_count", leaving
it as 0.

That means that before using it in drm_edp_backlight_enable() we need
to check to see if it's non-zero.

Programming this field to zero was confusing the panel I tested with
(Samsung ATNA33XC20). The backlight still worked somewhat but the
brightness values didn't correspond to what they should have been.

Fixes: 867cf9cd73c3 ("drm/dp: Extract i915's eDP backlight code into DRM helpers")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
---

(no changes since v1)

 drivers/gpu/drm/drm_dp_helper.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index b5f75ca05774..b8a5c5e49d74 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -3229,10 +3229,12 @@ int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct drm_edp_backli
 		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_dbg_kms(aux->drm_dev, "%s: Failed to write aux pwmgen bit count: %d\n",
-				    aux->name, ret);
+		if (bl->pwmgen_bit_count) {
+			ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, bl->pwmgen_bit_count);
+			if (ret != 1)
+				drm_dbg_kms(aux->drm_dev, "%s: Failed to write aux pwmgen bit count: %d\n",
+					aux->name, ret);
+		}
 	}
 
 	if (bl->pwm_freq_pre_divider) {
-- 
2.32.0.554.ge1b32706d8-goog

[PATCH v2 2/6] drm/bridge: ti-sn65dsi86: Fix power off sequence

[Douglas Anderson]

When testing with a panel that's apparently a little more persnickety
about the correct power sequence (specifically Samsung ATNA33XC20), we
found that the ti-sn65dsi86 was doing things just slightly wrong.

Looking closely at the ti-sn65dsi86's datasheet, the power off
sequence is supposed to be:
1. Clear VSTREAM_ENABLE bit
2. Stop DSI stream from GPU. DSI lanes must be placed in LP11 state.
3. Program the ML_TX_MODE to 0x0 (OFF)
4. Program the DP_NUM_LANES register to 0x0
5. Clear the DP_PLL_EN bit.
6. Deassert the EN pin.
7. Remove power from supply pins

Since we were doing the whole sequence in the "disable", I believe
that step #2 (stopping the DSI stream from the GPU) wasn't
happening. We also weren't setting DP_NUM_LANES to 0.

Let's fix this.

NOTE: things are a little asymmetric now. For instance, we turn the
PLL on in "enable" but now we're not turning it off until
"post_disable". It would seem to make sense to move the PLL turning on
to "pre_enable" to match. Unfortunately, I don't believe that's
allowed. It looks as if (in the non-refclk mode which probably nobody
is using) we have to wait until the MIPI clock is there before we can
enable the PLL. In any case, the way it is here won't really
hurt--it'll just leave the PLL on a little longer.

Fixes: a095f15c00e2 ("drm/bridge: add support for sn65dsi86 bridge driver")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Robert Foss <robert.foss@linaro.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
---

(no changes since v1)

 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 9bf889302bcc..5e932070a1c3 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -766,10 +766,6 @@ static void ti_sn_bridge_disable(struct drm_bridge *bridge)
 
 	/* disable video stream */
 	regmap_update_bits(pdata->regmap, SN_ENH_FRAME_REG, VSTREAM_ENABLE, 0);
-	/* semi auto link training mode OFF */
-	regmap_write(pdata->regmap, SN_ML_TX_MODE_REG, 0);
-	/* disable DP PLL */
-	regmap_write(pdata->regmap, SN_PLL_ENABLE_REG, 0);
 }
 
 static void ti_sn_bridge_set_dsi_rate(struct ti_sn65dsi86 *pdata)
@@ -1106,6 +1102,13 @@ static void ti_sn_bridge_post_disable(struct drm_bridge *bridge)
 {
 	struct ti_sn65dsi86 *pdata = bridge_to_ti_sn65dsi86(bridge);
 
+	/* semi auto link training mode OFF */
+	regmap_write(pdata->regmap, SN_ML_TX_MODE_REG, 0);
+	/* Num lanes to 0 as per power sequencing in data sheet */
+	regmap_update_bits(pdata->regmap, SN_SSC_CONFIG_REG, DP_NUM_LANES_MASK, 0);
+	/* disable DP PLL */
+	regmap_write(pdata->regmap, SN_PLL_ENABLE_REG, 0);
+
 	if (!pdata->refclk)
 		ti_sn65dsi86_disable_comms(pdata);
 
-- 
2.32.0.554.ge1b32706d8-goog

[PATCH v2 3/6] drm/bridge: ti-sn65dsi86: Add some 100 us delays

[Douglas Anderson]

The manual has always said that we need 100 us delays in a few
places. Though it hasn't seemed to be a big deal to skip these, let's
add them in case it makes something happier.

NOTE: this fixes no known issues but it seems good to make it right.

Fixes: a095f15c00e2 ("drm/bridge: add support for sn65dsi86 bridge driver")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Robert Foss <robert.foss@linaro.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
---

Changes in v2:
- Added Fixes tag as requested by Sam.

 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 5e932070a1c3..cd0fccdd8dfd 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -307,6 +307,9 @@ static int __maybe_unused ti_sn65dsi86_resume(struct device *dev)
 		return ret;
 	}
 
+	/* td2: min 100 us after regulators before enabling the GPIO */
+	usleep_range(100, 110);
+
 	gpiod_set_value(pdata->enable_gpio, 1);
 
 	/*
@@ -1096,6 +1099,9 @@ static void ti_sn_bridge_pre_enable(struct drm_bridge *bridge)
 
 	if (!pdata->refclk)
 		ti_sn65dsi86_enable_comms(pdata);
+
+	/* td7: min 100 us after enable before DSI data */
+	usleep_range(100, 110);
 }
 
 static void ti_sn_bridge_post_disable(struct drm_bridge *bridge)
-- 
2.32.0.554.ge1b32706d8-goog

[PATCH v2 4/6] Revert "drm/panel-simple: Add Samsung ATNA33XC20"

[Douglas Anderson]

This reverts commit 4bfe6c8f7c23b01719671b69fd29b87a35ccd9d6.

This panel's power sequencing really can't be handled properly by
panel-simple because of the special sequencing needed for the EL_ON3
GPIO. The only way it was sorta working in the past was by trying to
jam that signal into the "enable-gpio", but that really wasn't a good
fit. We'll add a custom panel driver for this panel to do it right.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
---

(no changes since v1)

 drivers/gpu/drm/panel/panel-simple.c | 33 ----------------------------
 1 file changed, 33 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
index 9b286bd4444f..c8694f7f8e0f 100644
--- a/drivers/gpu/drm/panel/panel-simple.c
+++ b/drivers/gpu/drm/panel/panel-simple.c
@@ -3621,36 +3621,6 @@ static const struct panel_desc rocktech_rk101ii01d_ct = {
 	.connector_type = DRM_MODE_CONNECTOR_LVDS,
 };
 
-static const struct drm_display_mode samsung_atna33xc20_mode = {
-	.clock = 138770,
-	.hdisplay = 1920,
-	.hsync_start = 1920 + 48,
-	.hsync_end = 1920 + 48 + 32,
-	.htotal = 1920 + 48 + 32 + 80,
-	.vdisplay = 1080,
-	.vsync_start = 1080 + 8,
-	.vsync_end = 1080 + 8 + 8,
-	.vtotal = 1080 + 8 + 8 + 16,
-	.flags = DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_NVSYNC,
-};
-
-static const struct panel_desc samsung_atna33xc20 = {
-	.modes = &samsung_atna33xc20_mode,
-	.num_modes = 1,
-	.bpc = 10,
-	.size = {
-		.width = 294,
-		.height = 165,
-	},
-	.delay = {
-		.disable_to_power_off = 200,
-		.power_to_enable = 400,
-		.hpd_absent_delay = 200,
-		.unprepare = 500,
-	},
-	.connector_type = DRM_MODE_CONNECTOR_eDP,
-};
-
 static const struct drm_display_mode samsung_lsn122dl01_c01_mode = {
 	.clock = 271560,
 	.hdisplay = 2560,
@@ -4657,9 +4627,6 @@ static const struct of_device_id platform_of_match[] = {
 	}, {
 		.compatible = "rocktech,rk101ii01d-ct",
 		.data = &rocktech_rk101ii01d_ct,
-	}, {
-		.compatible = "samsung,atna33xc20",
-		.data = &samsung_atna33xc20,
 	}, {
 		.compatible = "samsung,lsn122dl01-c01",
 		.data = &samsung_lsn122dl01_c01,
-- 
2.32.0.554.ge1b32706d8-goog

[PATCH v2 5/6] Revert "drm/panel-simple: Support for delays between GPIO & regulator"

[Douglas Anderson]

This reverts commit 18a1488bf1e13fc3fc96d7948466b2166067c6c8.

Those delays were added to support the Samsung ATNA33XC20
panel. However, we've moving that to its own panel driver and out of
panel-simple. That means we don't need the ability to specify this
delay.

NOTE: it's unlikely we want to keep this delay "just in case" some
other panel needs it. The enable-gpio and the power supply are really
supposed to be different ways to specify the same thing: the main
enable of the panel. Supporting a delay between them doesn't really
make sense.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
---

(no changes since v1)

 drivers/gpu/drm/panel/panel-simple.c | 28 ----------------------------
 1 file changed, 28 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
index c8694f7f8e0f..ff8b59471c71 100644
--- a/drivers/gpu/drm/panel/panel-simple.c
+++ b/drivers/gpu/drm/panel/panel-simple.c
@@ -132,22 +132,6 @@ struct panel_desc {
 		 */
 		unsigned int prepare_to_enable;
 
-		/**
-		 * @delay.power_to_enable: Time for the power to enable the display on.
-		 *
-		 * The time (in milliseconds) to wait after powering up the display
-		 * before asserting its enable pin.
-		 */
-		unsigned int power_to_enable;
-
-		/**
-		 * @delay.disable_to_power_off: Time for the disable to power the display off.
-		 *
-		 * The time (in milliseconds) to wait before powering off the display
-		 * after deasserting its enable pin.
-		 */
-		unsigned int disable_to_power_off;
-
 		/**
 		 * @delay.enable: Time for the panel to display a valid frame.
 		 *
@@ -363,10 +347,6 @@ static int panel_simple_suspend(struct device *dev)
 	struct panel_simple *p = dev_get_drvdata(dev);
 
 	gpiod_set_value_cansleep(p->enable_gpio, 0);
-
-	if (p->desc->delay.disable_to_power_off)
-		msleep(p->desc->delay.disable_to_power_off);
-
 	regulator_disable(p->supply);
 	p->unprepared_time = ktime_get();
 
@@ -427,9 +407,6 @@ static int panel_simple_prepare_once(struct panel_simple *p)
 		return err;
 	}
 
-	if (p->desc->delay.power_to_enable)
-		msleep(p->desc->delay.power_to_enable);
-
 	gpiod_set_value_cansleep(p->enable_gpio, 1);
 
 	delay = p->desc->delay.prepare;
@@ -803,11 +780,6 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc,
 		break;
 	}
 
-	if (!panel->enable_gpio && desc->delay.disable_to_power_off)
-		dev_warn(dev, "Need a delay after disabling panel GPIO, but a GPIO wasn't provided\n");
-	if (!panel->enable_gpio && desc->delay.power_to_enable)
-		dev_warn(dev, "Need a delay before enabling panel GPIO, but a GPIO wasn't provided\n");
-
 	dev_set_drvdata(dev, panel);
 
 	/*
-- 
2.32.0.554.ge1b32706d8-goog

[PATCH v2 6/6] drm/panel: atna33xc20: Introduce the Samsung ATNA33XC20 panel

[Douglas Anderson]

The Samsung ATNA33XC20 panel is an AMOLED eDP panel that has backlight
control over the DP AUX channel.

This panel is _almost_ able to be controlled in a "simple" way (and it
originally was implemented in panel-simple.c), but it's really
impossible to get the backlight semantics right there without adding
wacky special-case code to panel-simple. Let's give up and clone the
parts of panel-simple that we need and implement the power sequence
that this panel needs.

NOTE: we'll still leave the devicetree bindings alone. Even though the
power-sequencing is non-standard the bindings are still "simple".

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
---

(no changes since v1)

 drivers/gpu/drm/panel/Kconfig                 |  12 +
 drivers/gpu/drm/panel/Makefile                |   1 +
 .../gpu/drm/panel/panel-samsung-atna33xc20.c  | 366 ++++++++++++++++++
 3 files changed, 379 insertions(+)
 create mode 100644 drivers/gpu/drm/panel/panel-samsung-atna33xc20.c

diff --git a/drivers/gpu/drm/panel/Kconfig b/drivers/gpu/drm/panel/Kconfig
index 6b3eb041182c..58430d358489 100644
--- a/drivers/gpu/drm/panel/Kconfig
+++ b/drivers/gpu/drm/panel/Kconfig
@@ -353,6 +353,18 @@ config DRM_PANEL_RONBO_RB070D30
 	  Say Y here if you want to enable support for Ronbo Electronics
 	  RB070D30 1024x600 DSI panel.
 
+config DRM_PANEL_SAMSUNG_ATNA33XC20
+	tristate "Samsung ATNA33XC20 eDP panel"
+	depends on OF
+	depends on BACKLIGHT_CLASS_DEVICE
+	depends on PM
+	select VIDEOMODE_HELPERS
+	select DRM_DP_AUX_BUS
+	help
+	  DRM panel driver for the Samsung ATNA33XC20 panel. This panel can't
+	  be handled by the DRM_PANEL_SIMPLE driver because its power
+	  sequencing is non-standard.
+
 config DRM_PANEL_SAMSUNG_DB7430
 	tristate "Samsung DB7430-based DPI panels"
 	depends on OF && SPI && GPIOLIB
diff --git a/drivers/gpu/drm/panel/Makefile b/drivers/gpu/drm/panel/Makefile
index 08debae9b314..1b6fe2008861 100644
--- a/drivers/gpu/drm/panel/Makefile
+++ b/drivers/gpu/drm/panel/Makefile
@@ -34,6 +34,7 @@ obj-$(CONFIG_DRM_PANEL_RASPBERRYPI_TOUCHSCREEN) += panel-raspberrypi-touchscreen
 obj-$(CONFIG_DRM_PANEL_RAYDIUM_RM67191) += panel-raydium-rm67191.o
 obj-$(CONFIG_DRM_PANEL_RAYDIUM_RM68200) += panel-raydium-rm68200.o
 obj-$(CONFIG_DRM_PANEL_RONBO_RB070D30) += panel-ronbo-rb070d30.o
+obj-$(CONFIG_DRM_PANEL_SAMSUNG_ATNA33XC20) += panel-samsung-atna33xc20.o
 obj-$(CONFIG_DRM_PANEL_SAMSUNG_DB7430) += panel-samsung-db7430.o
 obj-$(CONFIG_DRM_PANEL_SAMSUNG_LD9040) += panel-samsung-ld9040.o
 obj-$(CONFIG_DRM_PANEL_SAMSUNG_S6D16D0) += panel-samsung-s6d16d0.o
diff --git a/drivers/gpu/drm/panel/panel-samsung-atna33xc20.c b/drivers/gpu/drm/panel/panel-samsung-atna33xc20.c
new file mode 100644
index 000000000000..221db6512859
--- /dev/null
+++ b/drivers/gpu/drm/panel/panel-samsung-atna33xc20.c
@@ -0,0 +1,366 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2021 Google Inc.
+ *
+ * Panel driver for the Samsung ATNA33XC20 panel. This panel can't be handled
+ * by the DRM_PANEL_SIMPLE driver because its power sequencing is non-standard.
+ */
+
+#include <linux/backlight.h>
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/pm_runtime.h>
+#include <linux/regulator/consumer.h>
+
+#include <drm/drm_dp_aux_bus.h>
+#include <drm/drm_dp_helper.h>
+#include <drm/drm_edid.h>
+#include <drm/drm_panel.h>
+
+struct atana33xc20_panel {
+	struct drm_panel base;
+	bool prepared;
+	bool enabled;
+	bool el3_was_on;
+
+	bool no_hpd;
+	struct gpio_desc *hpd_gpio;
+
+	struct regulator *supply;
+	struct gpio_desc *el_on3_gpio;
+
+	struct edid *edid;
+
+	ktime_t powered_off_time;
+	ktime_t powered_on_time;
+	ktime_t el_on3_off_time;
+};
+
+static inline struct atana33xc20_panel *to_atana33xc20(struct drm_panel *panel)
+{
+	return container_of(panel, struct atana33xc20_panel, base);
+}
+
+static void atana33xc20_wait(ktime_t start_ktime, unsigned int min_ms)
+{
+	ktime_t now_ktime, min_ktime;
+
+	min_ktime = ktime_add(start_ktime, ms_to_ktime(min_ms));
+	now_ktime = ktime_get();
+
+	if (ktime_before(now_ktime, min_ktime))
+		msleep(ktime_to_ms(ktime_sub(min_ktime, now_ktime)) + 1);
+}
+
+static int atana33xc20_suspend(struct device *dev)
+{
+	struct atana33xc20_panel *p = dev_get_drvdata(dev);
+	int ret;
+
+	/*
+	 * Note 3 (Example of power off sequence in detail) in spec
+	 * specifies to wait 150 ms after deasserting EL3_ON before
+	 * powering off.
+	 */
+	if (p->el3_was_on)
+		atana33xc20_wait(p->el_on3_off_time, 150);
+
+	ret = regulator_disable(p->supply);
+	if (ret)
+		return ret;
+	p->powered_off_time = ktime_get();
+	p->el3_was_on = false;
+
+	return 0;
+}
+
+static int atana33xc20_resume(struct device *dev)
+{
+	struct atana33xc20_panel *p = dev_get_drvdata(dev);
+	bool hpd_asserted = false;
+	int ret;
+
+	/* T12 (Power off time) is min 500 ms */
+	atana33xc20_wait(p->powered_off_time, 500);
+
+	ret = regulator_enable(p->supply);
+	if (ret)
+		return ret;
+	p->powered_on_time = ktime_get();
+
+	/*
+	 * Handle HPD. Note: if HPD is hooked up to a dedicated pin on the
+	 * eDP controller then "no_hpd" will be false _and_ "hpd_gpio" will be
+	 * NULL. It's up to the controller driver to wait for HPD after
+	 * preparing the panel in that case.
+	 */
+	if (p->no_hpd) {
+		/* T3 VCC to HPD high is max 200 ms */
+		msleep(200);
+	} else if (p->hpd_gpio) {
+		ret = readx_poll_timeout(gpiod_get_value_cansleep, p->hpd_gpio,
+					 hpd_asserted, hpd_asserted,
+					 1000, 200000);
+		if (!hpd_asserted)
+			dev_warn(dev, "Timeout waiting for HPD\n");
+	}
+
+	return 0;
+}
+
+static int atana33xc20_disable(struct drm_panel *panel)
+{
+	struct atana33xc20_panel *p = to_atana33xc20(panel);
+
+	/* Disabling when already disabled is a no-op */
+	if (!p->enabled)
+		return 0;
+
+	gpiod_set_value_cansleep(p->el_on3_gpio, 0);
+	p->el_on3_off_time = ktime_get();
+	p->enabled = false;
+
+	/*
+	 * Keep track of the fact that EL_ON3 was on but we haven't power
+	 * cycled yet. This lets us know that "el_on3_off_time" is recent (we
+	 * don't need to worry about ktime wraparounds) and also makes it
+	 * obvious if we try to enable again without a power cycle (see the
+	 * warning in atana33xc20_enable()).
+	 */
+	p->el3_was_on = true;
+
+	/*
+	 * Sleeping 20 ms here (after setting the GPIO) avoids a glitch when
+	 * powering off.
+	 */
+	msleep(20);
+
+	return 0;
+}
+
+static int atana33xc20_enable(struct drm_panel *panel)
+{
+	struct atana33xc20_panel *p = to_atana33xc20(panel);
+
+	/* Enabling when already enabled is a no-op */
+	if (p->enabled)
+		return 0;
+
+	/*
+	 * Once EL_ON3 drops we absolutely need a power cycle before the next
+	 * enable or the backlight will never come on again. The code ensures
+	 * this because disable() is _always_ followed by unprepare() and
+	 * unprepare() forces a suspend with pm_runtime_put_sync_suspend(),
+	 * but let's track just to make sure since the requirement is so
+	 * non-obvious.
+	 */
+	if (WARN_ON(p->el3_was_on))
+		return -EIO;
+
+	/*
+	 * Note 2 (Example of power on sequence in detail) in spec specifies
+	 * to wait 400 ms after powering on before asserting EL3_on.
+	 */
+	atana33xc20_wait(p->powered_on_time, 400);
+
+	gpiod_set_value_cansleep(p->el_on3_gpio, 1);
+	p->enabled = true;
+
+	return 0;
+}
+
+static int atana33xc20_unprepare(struct drm_panel *panel)
+{
+	struct atana33xc20_panel *p = to_atana33xc20(panel);
+	int ret;
+
+	/* Unpreparing when already unprepared is a no-op */
+	if (!p->prepared)
+		return 0;
+
+	/*
+	 * Purposely do a put_sync, don't use autosuspend. The panel's tcon
+	 * seems to sometimes crash when you stop giving it data and this is
+	 * the best way to ensure it will come back.
+	 *
+	 * NOTE: we still want autosuspend for cases where we only turn on
+	 * to get the EDID or otherwise send DP AUX commands to the panel.
+	 */
+	ret = pm_runtime_put_sync_suspend(panel->dev);
+	if (ret < 0)
+		return ret;
+	p->prepared = false;
+
+	return 0;
+}
+
+static int atana33xc20_prepare(struct drm_panel *panel)
+{
+	struct atana33xc20_panel *p = to_atana33xc20(panel);
+	int ret;
+
+	/* Preparing when already prepared is a no-op */
+	if (p->prepared)
+		return 0;
+
+	ret = pm_runtime_get_sync(panel->dev);
+	if (ret < 0) {
+		pm_runtime_put_autosuspend(panel->dev);
+		return ret;
+	}
+	p->prepared = true;
+
+	return 0;
+}
+
+static int atana33xc20_get_modes(struct drm_panel *panel,
+				 struct drm_connector *connector)
+{
+	struct atana33xc20_panel *p = to_atana33xc20(panel);
+	struct dp_aux_ep_device *aux_ep = to_dp_aux_ep_dev(panel->dev);
+	int num = 0;
+
+	pm_runtime_get_sync(panel->dev);
+
+	if (!p->edid)
+		p->edid = drm_get_edid(connector, &aux_ep->aux->ddc);
+	num = drm_add_edid_modes(connector, p->edid);
+
+	pm_runtime_mark_last_busy(panel->dev);
+	pm_runtime_put_autosuspend(panel->dev);
+
+	return num;
+}
+
+static const struct drm_panel_funcs atana33xc20_funcs = {
+	.disable = atana33xc20_disable,
+	.enable = atana33xc20_enable,
+	.unprepare = atana33xc20_unprepare,
+	.prepare = atana33xc20_prepare,
+	.get_modes = atana33xc20_get_modes,
+};
+
+static void atana33xc20_runtime_disable(void *data)
+{
+	pm_runtime_disable(data);
+}
+
+static void atana33xc20_dont_use_autosuspend(void *data)
+{
+	pm_runtime_dont_use_autosuspend(data);
+}
+
+static int atana33xc20_probe(struct dp_aux_ep_device *aux_ep)
+{
+	struct atana33xc20_panel *panel;
+	struct device *dev = &aux_ep->dev;
+	int ret;
+
+	panel = devm_kzalloc(dev, sizeof(*panel), GFP_KERNEL);
+	if (!panel)
+		return -ENOMEM;
+	dev_set_drvdata(dev, panel);
+
+	panel->supply = devm_regulator_get(dev, "power");
+	if (IS_ERR(panel->supply))
+		return dev_err_probe(dev, PTR_ERR(panel->supply),
+				     "Failed to get power supply\n");
+
+	panel->el_on3_gpio = devm_gpiod_get(dev, "enable", GPIOD_OUT_LOW);
+	if (IS_ERR(panel->el_on3_gpio))
+		return dev_err_probe(dev, PTR_ERR(panel->el_on3_gpio),
+				     "Failed to get enable GPIO\n");
+
+	panel->no_hpd = of_property_read_bool(dev->of_node, "no-hpd");
+	if (!panel->no_hpd) {
+		panel->hpd_gpio = devm_gpiod_get_optional(dev, "hpd", GPIOD_IN);
+		if (IS_ERR(panel->hpd_gpio))
+			return dev_err_probe(dev, PTR_ERR(panel->hpd_gpio),
+					     "Failed to get HPD GPIO\n");
+	}
+
+	pm_runtime_enable(dev);
+	ret = devm_add_action_or_reset(dev,  atana33xc20_runtime_disable, dev);
+	if (ret)
+		return ret;
+	pm_runtime_set_autosuspend_delay(dev, 1000);
+	pm_runtime_use_autosuspend(dev);
+	ret = devm_add_action_or_reset(dev,  atana33xc20_dont_use_autosuspend, dev);
+	if (ret)
+		return ret;
+
+	drm_panel_init(&panel->base, dev, &atana33xc20_funcs, DRM_MODE_CONNECTOR_eDP);
+
+	pm_runtime_get_sync(dev);
+	ret = drm_panel_dp_aux_backlight(&panel->base, aux_ep->aux);
+	pm_runtime_mark_last_busy(dev);
+	pm_runtime_put_autosuspend(dev);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "failed to register dp aux backlight\n");
+
+	drm_panel_add(&panel->base);
+
+	return 0;
+}
+
+static void atana33xc20_remove(struct dp_aux_ep_device *aux_ep)
+{
+	struct device *dev = &aux_ep->dev;
+	struct atana33xc20_panel *panel = dev_get_drvdata(dev);
+
+	drm_panel_remove(&panel->base);
+	drm_panel_disable(&panel->base);
+	drm_panel_unprepare(&panel->base);
+
+	kfree(panel->edid);
+}
+
+static void atana33xc20_shutdown(struct dp_aux_ep_device *aux_ep)
+{
+	struct device *dev = &aux_ep->dev;
+	struct atana33xc20_panel *panel = dev_get_drvdata(dev);
+
+	drm_panel_disable(&panel->base);
+	drm_panel_unprepare(&panel->base);
+}
+
+static const struct of_device_id atana33xc20_dt_match[] = {
+	{ .compatible = "samsung,atna33xc20", },
+	{ /* sentinal */ }
+};
+MODULE_DEVICE_TABLE(of, atana33xc20_dt_match);
+
+static const struct dev_pm_ops atana33xc20_pm_ops = {
+	SET_RUNTIME_PM_OPS(atana33xc20_suspend, atana33xc20_resume, NULL)
+	SET_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend,
+				pm_runtime_force_resume)
+};
+
+static struct dp_aux_ep_driver atana33xc20_driver = {
+	.driver = {
+		.name		= "samsung_atana33xc20",
+		.of_match_table = atana33xc20_dt_match,
+		.pm		= &atana33xc20_pm_ops,
+	},
+	.probe = atana33xc20_probe,
+	.remove = atana33xc20_remove,
+	.shutdown = atana33xc20_shutdown,
+};
+
+static int __init atana33xc20_init(void)
+{
+	return dp_aux_dp_driver_register(&atana33xc20_driver);
+}
+module_init(atana33xc20_init);
+
+static void __exit atana33xc20_exit(void)
+{
+	dp_aux_dp_driver_unregister(&atana33xc20_driver);
+}
+module_exit(atana33xc20_exit);
+
+MODULE_DESCRIPTION("Samsung ATANA33XC20 Panel Driver");
+MODULE_LICENSE("GPL v2");
-- 
2.32.0.554.ge1b32706d8-goog