[PATCH v4 0/4] drm/dp: Introduce wait_hpd_asserted() for the DP AUX bus

[PATCH v4 0/4] drm/dp: Introduce wait_hpd_asserted() for the DP AUX bus

[Douglas Anderson]

This is the 2nd four patches from my RFC series ("drm/dp: Improvements
for DP AUX channel") [1]. I've broken the series in two so we can make
progress on the two halves separately.

v2 of this series changes to add wait_hpd_asserted() instead of
is_hpd_asserted(). This allows us to move the extra delay needed for
ps8640 into the ps8640 driver itself.

The idea for this series came up during the review process of
Sankeerth's series trying to add eDP for Qualcomm SoCs [2].

This _doesn't_ attempt to fix the Analogix driver. If this works out,
ideally someone can post a patch up to do that.

[1] https://lore.kernel.org/r/20220409023628.2104952-1-dianders@chromium.org/
[2] https://lore.kernel.org/r/1648656179-10347-2-git-send-email-quic_sbillaka@quicinc.com/

Changes in v4:
- Add comment that caller powered up the panel.
- Comments now explain that we may wait longer due to debouncing.
- Mention in commit message debouncing vs. powering on timing.
- Rebased to handle the fact that the stuct moved files.
- Reorganized logic as per Dmitry's suggestion.

Changes in v3:
- Don't check "hpd_asserted" boolean when unset.
- Handle errors from gpiod_get_value_cansleep() properly.

Changes in v2:
- Change is_hpd_asserted() to wait_hpd_asserted()

Douglas Anderson (4):
  drm/dp: Add wait_hpd_asserted() callback to struct drm_dp_aux
  drm/panel-edp: Take advantage of wait_hpd_asserted() in struct
    drm_dp_aux
  drm/panel: atna33xc20: Take advantage of wait_hpd_asserted() in struct
    drm_dp_aux
  drm/bridge: parade-ps8640: Provide wait_hpd_asserted() in struct
    drm_dp_aux

 drivers/gpu/drm/bridge/parade-ps8640.c        | 39 +++++++++-----
 drivers/gpu/drm/panel/panel-edp.c             | 33 ++++++++----
 .../gpu/drm/panel/panel-samsung-atna33xc20.c  | 51 ++++++++++++++-----
 include/drm/display/drm_dp_helper.h           | 30 +++++++++++
 4 files changed, 117 insertions(+), 36 deletions(-)

-- 
2.36.1.476.g0c4daa206d-goog

[PATCH v4 1/4] drm/dp: Add wait_hpd_asserted() callback to struct drm_dp_aux

[Douglas Anderson]

Sometimes it's useful for users of the DP AUX bus (like panels) to be
able to poll HPD. Let's add a callback that allows DP AUX busses
drivers to provide this.

Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
---

Changes in v4:
- Comments now explain that we may wait longer due to debouncing.
- Rebased to handle the fact that the stuct moved files.

Changes in v2:
- Change is_hpd_asserted() to wait_hpd_asserted()

 include/drm/display/drm_dp_helper.h | 30 +++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h
index c5f8f45511ed..db0fe9f8a612 100644
--- a/include/drm/display/drm_dp_helper.h
+++ b/include/drm/display/drm_dp_helper.h
@@ -389,6 +389,36 @@ struct drm_dp_aux {
 	ssize_t (*transfer)(struct drm_dp_aux *aux,
 			    struct drm_dp_aux_msg *msg);
 
+	/**
+	 * @wait_hpd_asserted: wait for HPD to be asserted
+	 *
+	 * This is mainly useful for eDP panels drivers to wait for an eDP
+	 * panel to finish powering on. This is an optional function.
+	 *
+	 * This function will efficiently wait for the HPD signal to be
+	 * asserted. The `wait_us` parameter that is passed in says that we
+	 * know that the HPD signal is expected to be asserted within `wait_us`
+	 * microseconds. This function could wait for longer than `wait_us` if
+	 * the logic in the DP controller has a long debouncing time. The
+	 * important thing is that if this function returns success that the
+	 * DP controller is ready to send AUX transactions.
+	 *
+	 * This function returns 0 if HPD was asserted or -ETIMEDOUT if time
+	 * expired and HPD wasn't asserted. This function should not print
+	 * timeout errors to the log.
+	 *
+	 * The semantics of this function are designed to match the
+	 * readx_poll_timeout() function. That means a `wait_us` of 0 means
+	 * to wait forever. Like readx_poll_timeout(), this function may sleep.
+	 *
+	 * NOTE: this function specifically reports the state of the HPD pin
+	 * that's associated with the DP AUX channel. This is different from
+	 * the HPD concept in much of the rest of DRM which is more about
+	 * physical presence of a display. For eDP, for instance, a display is
+	 * assumed always present even if the HPD pin is deasserted.
+	 */
+	int (*wait_hpd_asserted)(struct drm_dp_aux *aux, unsigned long wait_us);
+
 	/**
 	 * @i2c_nack_count: Counts I2C NACKs, used for DP validation.
 	 */
-- 
2.36.1.476.g0c4daa206d-goog

[PATCH v4 2/4] drm/panel-edp: Take advantage of wait_hpd_asserted() in struct drm_dp_aux

[Douglas Anderson]

Let's add support for being able to read the HPD pin even if it's
hooked directly to the controller. This will allow us to get more
accurate delays also lets us take away the waiting in the AUX transfer
functions of the eDP controller drivers.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
---

(no changes since v2)

Changes in v2:
- Change is_hpd_asserted() to wait_hpd_asserted()

 drivers/gpu/drm/panel/panel-edp.c | 33 +++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-edp.c b/drivers/gpu/drm/panel/panel-edp.c
index c96014464355..ce5821132151 100644
--- a/drivers/gpu/drm/panel/panel-edp.c
+++ b/drivers/gpu/drm/panel/panel-edp.c
@@ -417,6 +417,11 @@ static int panel_edp_get_hpd_gpio(struct device *dev, struct panel_edp *p)
 	return 0;
 }
 
+static bool panel_edp_can_read_hpd(struct panel_edp *p)
+{
+	return !p->no_hpd && (p->hpd_gpio || (p->aux && p->aux->wait_hpd_asserted));
+}
+
 static int panel_edp_prepare_once(struct panel_edp *p)
 {
 	struct device *dev = p->base.dev;
@@ -441,17 +446,21 @@ static int panel_edp_prepare_once(struct panel_edp *p)
 	if (delay)
 		msleep(delay);
 
-	if (p->hpd_gpio) {
+	if (panel_edp_can_read_hpd(p)) {
 		if (p->desc->delay.hpd_absent)
 			hpd_wait_us = p->desc->delay.hpd_absent * 1000UL;
 		else
 			hpd_wait_us = 2000000;
 
-		err = readx_poll_timeout(gpiod_get_value_cansleep, p->hpd_gpio,
-					 hpd_asserted, hpd_asserted,
-					 1000, hpd_wait_us);
-		if (hpd_asserted < 0)
-			err = hpd_asserted;
+		if (p->hpd_gpio) {
+			err = readx_poll_timeout(gpiod_get_value_cansleep,
+						 p->hpd_gpio, hpd_asserted,
+						 hpd_asserted, 1000, hpd_wait_us);
+			if (hpd_asserted < 0)
+				err = hpd_asserted;
+		} else {
+			err = p->aux->wait_hpd_asserted(p->aux, hpd_wait_us);
+		}
 
 		if (err) {
 			if (err != -ETIMEDOUT)
@@ -532,18 +541,22 @@ static int panel_edp_enable(struct drm_panel *panel)
 	/*
 	 * If there is a "prepare_to_enable" delay then that's supposed to be
 	 * the delay from HPD going high until we can turn the backlight on.
-	 * However, we can only count this if HPD is handled by the panel
-	 * driver, not if it goes to a dedicated pin on the controller.
+	 * However, we can only count this if HPD is readable by the panel
+	 * driver.
+	 *
 	 * If we aren't handling the HPD pin ourselves then the best we
 	 * can do is assume that HPD went high immediately before we were
-	 * called (and link training took zero time).
+	 * called (and link training took zero time). Note that "no-hpd"
+	 * actually counts as handling HPD ourselves since we're doing the
+	 * worst case delay (in prepare) ourselves.
 	 *
 	 * NOTE: if we ever end up in this "if" statement then we're
 	 * guaranteed that the panel_edp_wait() call below will do no delay.
 	 * It already handles that case, though, so we don't need any special
 	 * code for it.
 	 */
-	if (p->desc->delay.prepare_to_enable && !p->hpd_gpio && !p->no_hpd)
+	if (p->desc->delay.prepare_to_enable &&
+	    !panel_edp_can_read_hpd(p) && !p->no_hpd)
 		delay = max(delay, p->desc->delay.prepare_to_enable);
 
 	if (delay)
-- 
2.36.1.476.g0c4daa206d-goog

[PATCH v4 3/4] drm/panel: atna33xc20: Take advantage of wait_hpd_asserted() in struct drm_dp_aux

[Douglas Anderson]

Let's add support for being able to read the HPD pin even if it's
hooked directly to the controller. This will let us take away the
waiting in the AUX transfer functions of the eDP controller drivers.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

Changes in v4:
- Reorganized logic as per Dmitry's suggestion.

Changes in v3:
- Don't check "hpd_asserted" boolean when unset.
- Handle errors from gpiod_get_value_cansleep() properly.

Changes in v2:
- Change is_hpd_asserted() to wait_hpd_asserted()

 .../gpu/drm/panel/panel-samsung-atna33xc20.c  | 51 ++++++++++++++-----
 1 file changed, 38 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-samsung-atna33xc20.c b/drivers/gpu/drm/panel/panel-samsung-atna33xc20.c
index 3dd10412d147..5a8b978c6415 100644
--- a/drivers/gpu/drm/panel/panel-samsung-atna33xc20.c
+++ b/drivers/gpu/drm/panel/panel-samsung-atna33xc20.c
@@ -19,6 +19,10 @@
 #include <drm/drm_edid.h>
 #include <drm/drm_panel.h>
 
+/* T3 VCC to HPD high is max 200 ms */
+#define HPD_MAX_MS	200
+#define HPD_MAX_US	(HPD_MAX_MS * 1000)
+
 struct atana33xc20_panel {
 	struct drm_panel base;
 	bool prepared;
@@ -30,6 +34,7 @@ struct atana33xc20_panel {
 
 	struct regulator *supply;
 	struct gpio_desc *el_on3_gpio;
+	struct drm_dp_aux *aux;
 
 	struct edid *edid;
 
@@ -79,7 +84,7 @@ static int atana33xc20_suspend(struct device *dev)
 static int atana33xc20_resume(struct device *dev)
 {
 	struct atana33xc20_panel *p = dev_get_drvdata(dev);
-	bool hpd_asserted = false;
+	int hpd_asserted;
 	int ret;
 
 	/* T12 (Power off time) is min 500 ms */
@@ -90,23 +95,41 @@ static int atana33xc20_resume(struct device *dev)
 		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) {
+		msleep(HPD_MAX_MS);
+		return 0;
+	}
+
+	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");
+					 1000, HPD_MAX_US);
+		if (hpd_asserted < 0)
+			ret = hpd_asserted;
+
+		if (ret)
+			dev_warn(dev, "Error waiting for HPD GPIO: %d\n", ret);
+
+		return ret;
 	}
 
+	if (p->aux->wait_hpd_asserted) {
+		ret = p->aux->wait_hpd_asserted(p->aux, HPD_MAX_US);
+
+		if (ret)
+			dev_warn(dev, "Controller error waiting for HPD: %d\n", ret);
+
+		return ret;
+	}
+
+	/*
+	 * Note that it's possible that no_hpd is false, hpd_gpio is
+	 * NULL, and wait_hpd_asserted is NULL. This is because
+	 * wait_hpd_asserted() is optional even if HPD is hooked up to
+	 * a dedicated pin on the eDP controller. In this case we just
+	 * assume that the controller driver will wait for HPD at the
+	 * right times.
+	 */
 	return 0;
 }
 
@@ -263,6 +286,8 @@ static int atana33xc20_probe(struct dp_aux_ep_device *aux_ep)
 		return -ENOMEM;
 	dev_set_drvdata(dev, panel);
 
+	panel->aux = aux_ep->aux;
+
 	panel->supply = devm_regulator_get(dev, "power");
 	if (IS_ERR(panel->supply))
 		return dev_err_probe(dev, PTR_ERR(panel->supply),
-- 
2.36.1.476.g0c4daa206d-goog

[PATCH v4 4/4] drm/bridge: parade-ps8640: Provide wait_hpd_asserted() in struct drm_dp_aux

[Douglas Anderson]

This implements the callback added by the patch ("drm/dp: Add
wait_hpd_asserted() callback to struct drm_dp_aux").

With this change and all the two "DP AUX Endpoint" drivers changed to
use wait_hpd_asserted(), we no longer need to have an long delay in
the AUX transfer function. It's up to the panel code to make sure that
the panel is powered now. If someone tried to call the aux transfer
function without making sure the panel is powered we'll just get a
normal transfer failure.

We'll still keep the wait for HPD in the pre_enable() function. Though
it's probably not actually needed there, this driver is used in the
old mode (pre-DP AUX Endpoints) and it may be important for those
cases. If nothing else, it shouldn't cause any big problems.

NOTE: When handling the timeout for HPD we start the timer _after_
we've runtime resumed the device. This is definitely important for the
panel on my homestar which comes up 170 ms after we start timing (the
panel specifies 200 ms max). It's a little unclear how much of this
extra time is due to some internal state machine in the parade
firmware vs. debouncing but it seems to work for the two test cases I
have to do it this way.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
---

Changes in v4:
- Add comment that caller powered up the panel.
- Mention in commit message debouncing vs. powering on timing.

Changes in v2:
- Change is_hpd_asserted() to wait_hpd_asserted()

 drivers/gpu/drm/bridge/parade-ps8640.c | 39 +++++++++++++++++---------
 1 file changed, 26 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
index ff4227f6d800..e880eee55822 100644
--- a/drivers/gpu/drm/bridge/parade-ps8640.c
+++ b/drivers/gpu/drm/bridge/parade-ps8640.c
@@ -168,23 +168,35 @@ static bool ps8640_of_panel_on_aux_bus(struct device *dev)
 	return true;
 }
 
-static int ps8640_ensure_hpd(struct ps8640 *ps_bridge)
+static int _ps8640_wait_hpd_asserted(struct ps8640 *ps_bridge, unsigned long wait_us)
 {
 	struct regmap *map = ps_bridge->regmap[PAGE2_TOP_CNTL];
-	struct device *dev = &ps_bridge->page[PAGE2_TOP_CNTL]->dev;
 	int status;
-	int ret;
 
 	/*
 	 * Apparently something about the firmware in the chip signals that
 	 * HPD goes high by reporting GPIO9 as high (even though HPD isn't
 	 * actually connected to GPIO9).
 	 */
-	ret = regmap_read_poll_timeout(map, PAGE2_GPIO_H, status,
-				       status & PS_GPIO9, 20 * 1000, 200 * 1000);
+	return regmap_read_poll_timeout(map, PAGE2_GPIO_H, status,
+					status & PS_GPIO9, wait_us / 10, wait_us);
+}
 
-	if (ret < 0)
-		dev_warn(dev, "HPD didn't go high: %d\n", ret);
+static int ps8640_wait_hpd_asserted(struct drm_dp_aux *aux, unsigned long wait_us)
+{
+	struct ps8640 *ps_bridge = aux_to_ps8640(aux);
+	struct device *dev = &ps_bridge->page[PAGE0_DP_CNTL]->dev;
+	int ret;
+
+	/*
+	 * Note that this function is called by code that has already powered
+	 * the panel. We have to power ourselves up but we don't need to worry
+	 * about powering the panel.
+	 */
+	pm_runtime_get_sync(dev);
+	ret = _ps8640_wait_hpd_asserted(ps_bridge, wait_us);
+	pm_runtime_mark_last_busy(dev);
+	pm_runtime_put_autosuspend(dev);
 
 	return ret;
 }
@@ -323,9 +335,7 @@ static ssize_t ps8640_aux_transfer(struct drm_dp_aux *aux,
 	int ret;
 
 	pm_runtime_get_sync(dev);
-	ret = ps8640_ensure_hpd(ps_bridge);
-	if (!ret)
-		ret = ps8640_aux_transfer_msg(aux, msg);
+	ret = ps8640_aux_transfer_msg(aux, msg);
 	pm_runtime_mark_last_busy(dev);
 	pm_runtime_put_autosuspend(dev);
 
@@ -369,8 +379,8 @@ static int __maybe_unused ps8640_resume(struct device *dev)
 	 * Mystery 200 ms delay for the "MCU to be ready". It's unclear if
 	 * this is truly necessary since the MCU will already signal that
 	 * things are "good to go" by signaling HPD on "gpio 9". See
-	 * ps8640_ensure_hpd(). For now we'll keep this mystery delay just in
-	 * case.
+	 * _ps8640_wait_hpd_asserted(). For now we'll keep this mystery delay
+	 * just in case.
 	 */
 	msleep(200);
 
@@ -406,7 +416,9 @@ static void ps8640_pre_enable(struct drm_bridge *bridge)
 	int ret;
 
 	pm_runtime_get_sync(dev);
-	ps8640_ensure_hpd(ps_bridge);
+	ret = _ps8640_wait_hpd_asserted(ps_bridge, 200 * 1000);
+	if (ret < 0)
+		dev_warn(dev, "HPD didn't go high: %d\n", ret);
 
 	/*
 	 * The Manufacturer Command Set (MCS) is a device dependent interface
@@ -682,6 +694,7 @@ static int ps8640_probe(struct i2c_client *client)
 	ps_bridge->aux.name = "parade-ps8640-aux";
 	ps_bridge->aux.dev = dev;
 	ps_bridge->aux.transfer = ps8640_aux_transfer;
+	ps_bridge->aux.wait_hpd_asserted = ps8640_wait_hpd_asserted;
 	drm_dp_aux_init(&ps_bridge->aux);
 
 	pm_runtime_enable(dev);
-- 
2.36.1.476.g0c4daa206d-goog

Re: [PATCH v4 3/4] drm/panel: atna33xc20: Take advantage of wait_hpd_asserted() in struct drm_dp_aux

[Dmitry Baryshkov]

On Wed, 15 Jun 2022 at 00:54, Douglas Anderson <dianders@chromium.org> wrote:
>
> Let's add support for being able to read the HPD pin even if it's
> hooked directly to the controller. This will let us take away the
> waiting in the AUX transfer functions of the eDP controller drivers.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

> ---
>
> Changes in v4:
> - Reorganized logic as per Dmitry's suggestion.
>
> Changes in v3:
> - Don't check "hpd_asserted" boolean when unset.
> - Handle errors from gpiod_get_value_cansleep() properly.
>
> Changes in v2:
> - Change is_hpd_asserted() to wait_hpd_asserted()
>
>  .../gpu/drm/panel/panel-samsung-atna33xc20.c  | 51 ++++++++++++++-----
>  1 file changed, 38 insertions(+), 13 deletions(-)
>

-- 
With best wishes
Dmitry

Re: [PATCH v4 0/4] drm/dp: Introduce wait_hpd_asserted() for the DP AUX bus

[Doug Anderson]

Hi,

On Tue, Jun 14, 2022 at 2:54 PM Douglas Anderson <dianders@chromium.org> wrote:
>
> This is the 2nd four patches from my RFC series ("drm/dp: Improvements
> for DP AUX channel") [1]. I've broken the series in two so we can make
> progress on the two halves separately.
>
> v2 of this series changes to add wait_hpd_asserted() instead of
> is_hpd_asserted(). This allows us to move the extra delay needed for
> ps8640 into the ps8640 driver itself.
>
> The idea for this series came up during the review process of
> Sankeerth's series trying to add eDP for Qualcomm SoCs [2].
>
> This _doesn't_ attempt to fix the Analogix driver. If this works out,
> ideally someone can post a patch up to do that.
>
> [1] https://lore.kernel.org/r/20220409023628.2104952-1-dianders@chromium.org/
> [2] https://lore.kernel.org/r/1648656179-10347-2-git-send-email-quic_sbillaka@quicinc.com/
>
> Changes in v4:
> - Add comment that caller powered up the panel.
> - Comments now explain that we may wait longer due to debouncing.
> - Mention in commit message debouncing vs. powering on timing.
> - Rebased to handle the fact that the stuct moved files.
> - Reorganized logic as per Dmitry's suggestion.
>
> Changes in v3:
> - Don't check "hpd_asserted" boolean when unset.
> - Handle errors from gpiod_get_value_cansleep() properly.
>
> Changes in v2:
> - Change is_hpd_asserted() to wait_hpd_asserted()
>
> Douglas Anderson (4):
>   drm/dp: Add wait_hpd_asserted() callback to struct drm_dp_aux
>   drm/panel-edp: Take advantage of wait_hpd_asserted() in struct
>     drm_dp_aux
>   drm/panel: atna33xc20: Take advantage of wait_hpd_asserted() in struct
>     drm_dp_aux
>   drm/bridge: parade-ps8640: Provide wait_hpd_asserted() in struct
>     drm_dp_aux
>
>  drivers/gpu/drm/bridge/parade-ps8640.c        | 39 +++++++++-----
>  drivers/gpu/drm/panel/panel-edp.c             | 33 ++++++++----
>  .../gpu/drm/panel/panel-samsung-atna33xc20.c  | 51 ++++++++++++++-----
>  include/drm/display/drm_dp_helper.h           | 30 +++++++++++
>  4 files changed, 117 insertions(+), 36 deletions(-)

Pushed to drm-misc-next with Dmitry's reviews.

f5aa7d46b0ee drm/bridge: parade-ps8640: Provide wait_hpd_asserted() in
struct drm_dp_aux
3b5765df375c drm/panel: atna33xc20: Take advantage of
wait_hpd_asserted() in struct drm_dp_aux
2327b13d6c47 drm/panel-edp: Take advantage of wait_hpd_asserted() in
struct drm_dp_aux
841d742f094e drm/dp: Add wait_hpd_asserted() callback to struct drm_dp_aux

-Doug