[v7] drm/msm/dp: force link training for display resolution change

Display resolution change is implemented through drm modeset. Older
modeset (resolution) has to be disabled first before newer modeset
(resolution) can be enabled. Display disable will turn off both
pixel clock and main link clock so that main link have to be
re-trained during display enable to have new video stream flow
again. At current implementation, display enable function manually
kicks up irq_hpd_handle which will read panel link status and start
link training if link status is not in sync state.

However, there is rare case that a particular panel links status keep
staying in sync for some period of time after main link had been shut
down previously at display disabled. In this case, main link retraining
will not be executed by irq_hdp_handle(). Hence video stream of newer
display resolution will fail to be transmitted to panel due to main
link is not in sync between host and panel.

This patch will bypass irq_hpd_handle() in favor of directly call
dp_ctrl_on_stream() to always perform link training in regardless of
main link status. So that no unexpected exception resolution change
failure cases will happen. Also this implementation are more efficient
than manual kicking off irq_hpd_handle function.

Changes in v2:
-- set force_link_train flag on DP only (is_edp == false)

Changes in v3:
-- revise commit  text
-- add Fixes tag

Changes in v4:
-- revise commit  text

Changes in v5:
-- fix spelling at commit text

Changes in v6:
-- split dp_ctrl_on_stream() for phy test case
-- revise commit text for modeset

Changes in v7:
-- drop 0 assignment at local variable (ret = 0)

Fixes: 62671d2ef24b ("drm/msm/dp: fixes wrong connection state caused by failure of link train")
Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
---
 drivers/gpu/drm/msm/dp/dp_ctrl.c    | 31 +++++++++++++++++++++++--------
 drivers/gpu/drm/msm/dp/dp_ctrl.h    |  3 ++-
 drivers/gpu/drm/msm/dp/dp_display.c | 13 ++++++-------
 3 files changed, 31 insertions(+), 16 deletions(-)

Quoting Kuogee Hsieh (2022-06-15 08:53:57)
> Display resolution change is implemented through drm modeset. Older
> modeset (resolution) has to be disabled first before newer modeset
> (resolution) can be enabled. Display disable will turn off both
> pixel clock and main link clock so that main link have to be
> re-trained during display enable to have new video stream flow
> again. At current implementation, display enable function manually
> kicks up irq_hpd_handle which will read panel link status and start
> link training if link status is not in sync state.
>
> However, there is rare case that a particular panel links status keep
> staying in sync for some period of time after main link had been shut
> down previously at display disabled. In this case, main link retraining
> will not be executed by irq_hdp_handle(). Hence video stream of newer
> display resolution will fail to be transmitted to panel due to main
> link is not in sync between host and panel.
>
> This patch will bypass irq_hpd_handle() in favor of directly call
> dp_ctrl_on_stream() to always perform link training in regardless of
> main link status. So that no unexpected exception resolution change
> failure cases will happen. Also this implementation are more efficient
> than manual kicking off irq_hpd_handle function.
>
> Changes in v2:
> -- set force_link_train flag on DP only (is_edp == false)
>
> Changes in v3:
> -- revise commit  text
> -- add Fixes tag
>
> Changes in v4:
> -- revise commit  text
>
> Changes in v5:
> -- fix spelling at commit text
>
> Changes in v6:
> -- split dp_ctrl_on_stream() for phy test case
> -- revise commit text for modeset
>
> Changes in v7:
> -- drop 0 assignment at local variable (ret = 0)
>
> Fixes: 62671d2ef24b ("drm/msm/dp: fixes wrong connection state caused by failure of link train")
> Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_ctrl.c    | 31 +++++++++++++++++++++++--------
>  drivers/gpu/drm/msm/dp/dp_ctrl.h    |  3 ++-
>  drivers/gpu/drm/msm/dp/dp_display.c | 13 ++++++-------
>  3 files changed, 31 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index af7a80c..01028b5 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1551,7 +1551,7 @@ static int dp_ctrl_process_phy_test_request(struct dp_ctrl_private *ctrl)
>
>         ret = dp_ctrl_on_link(&ctrl->dp_ctrl);
>         if (!ret)
> -               ret = dp_ctrl_on_stream(&ctrl->dp_ctrl);
> +               ret = dp_ctrl_on_stream_phy_test_report(&ctrl->dp_ctrl);
>         else
>                 DRM_ERROR("failed to enable DP link controller\n");
>
> @@ -1807,7 +1807,27 @@ static int dp_ctrl_link_retrain(struct dp_ctrl_private *ctrl)
>         return dp_ctrl_setup_main_link(ctrl, &training_step);
>  }
>
> -int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
> +int dp_ctrl_on_stream_phy_test_report(struct dp_ctrl *dp_ctrl)
> +{
> +       int ret;
> +       struct dp_ctrl_private *ctrl;
> +
> +       ctrl = container_of(dp_ctrl, struct dp_ctrl_private, dp_ctrl);
> +
> +       ctrl->dp_ctrl.pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;

There are a few different places where we assign 'pixel_rate' in this
file. Can they be consolidated? Is it a concern that wide_bus isn't
considered here? I was really hoping that we could reuse code instead of
duplicate it, DRY principle and all.

Maybe even better, can we remove 'pixel_rate' entirely from being
stashed? See further down for my patch.

> +
> +       ret = dp_ctrl_enable_stream_clocks(ctrl);
> +       if (ret) {
> +               DRM_ERROR("Failed to start pixel clocks. ret=%d\n", ret);
> +               return ret;
> +       }
> +
> +       dp_ctrl_send_phy_test_pattern(ctrl);
> +
> +       return 0;
> +}
> +
> +int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl, bool force_link_train)
>  {
>         int ret = 0;
>         bool mainlink_ready = false;
> @@ -1843,12 +1863,7 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
>                 goto end;
>         }
>
> -       if (ctrl->link->sink_request & DP_TEST_LINK_PHY_TEST_PATTERN) {
> -               dp_ctrl_send_phy_test_pattern(ctrl);
> -               return 0;
> -       }
> -
> -       if (!dp_ctrl_channel_eq_ok(ctrl))
> +       if (force_link_train || !dp_ctrl_channel_eq_ok(ctrl))
>                 dp_ctrl_link_retrain(ctrl);
>
>         /* stop txing train pattern to end link training */
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.h b/drivers/gpu/drm/msm/dp/dp_ctrl.h
> index 0745fde..9a39b00 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.h
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.h
> @@ -21,7 +21,8 @@ struct dp_ctrl {
>  };
>
>  int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl);
> -int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl);
> +int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl, bool force_link_train);
> +int dp_ctrl_on_stream_phy_test_report(struct dp_ctrl *dp_ctrl);

Please don't expose the API if it's only used in dp_ctrl.c

>  int dp_ctrl_off_link_stream(struct dp_ctrl *dp_ctrl);
>  int dp_ctrl_off_link(struct dp_ctrl *dp_ctrl);
>  int dp_ctrl_off(struct dp_ctrl *dp_ctrl);
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index c388323..b6d25ab 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -872,7 +872,7 @@ static int dp_display_enable(struct dp_display_private *dp, u32 data)
>                 return 0;
>         }
>
> -       rc = dp_ctrl_on_stream(dp->ctrl);
> +       rc = dp_ctrl_on_stream(dp->ctrl, data);
>         if (!rc)
>                 dp_display->power_on = true;
>
> @@ -1654,6 +1654,7 @@ void dp_bridge_enable(struct drm_bridge *drm_bridge)
>         int rc = 0;
>         struct dp_display_private *dp_display;
>         u32 state;
> +       bool force_link_train = false;
>
>         dp_display = container_of(dp, struct dp_display_private, dp_display);
>         if (!dp_display->dp_mode.drm_mode.clock) {
> @@ -1688,10 +1689,12 @@ void dp_bridge_enable(struct drm_bridge *drm_bridge)
>
>         state =  dp_display->hpd_state;
>
> -       if (state == ST_DISPLAY_OFF)
> +       if (state == ST_DISPLAY_OFF) {
>                 dp_display_host_phy_init(dp_display);
> +               force_link_train = true;
> +       }
>
> -       dp_display_enable(dp_display, 0);
> +       dp_display_enable(dp_display, force_link_train);

I see now that ST_DISPLAY_OFF isn't exposed outside of this file. So my
hope to not modify the function argument is not possible, ok.

>
>         rc = dp_display_post_enable(dp);
>         if (rc) {

Here's my untested patch for pixel_rate removal and movement of the code
so we don't have to expose the test API. Note that there's a place where
I removed the setting of the pixel_rate but didn't use it (see
dp_ctrl_link_maintenance()). Is that important? I couldn't figure out
how link maintenance cared about the pixel rate.

---8<----
diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
index b4e333a4c587..e114521af2e9 100644
--- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
+++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
@@ -1238,8 +1238,6 @@ static int dp_ctrl_link_train_2(struct
dp_ctrl_private *ctrl,
 	return -ETIMEDOUT;
 }

-static int dp_ctrl_reinitialize_mainlink(struct dp_ctrl_private *ctrl);
-
 static int dp_ctrl_link_train(struct dp_ctrl_private *ctrl,
 			int *training_step)
 {
@@ -1338,7 +1336,7 @@ static void dp_ctrl_set_clock_rate(struct
dp_ctrl_private *ctrl,
 				name, rate);
 }

-static int dp_ctrl_enable_mainlink_clocks(struct dp_ctrl_private *ctrl)
+static int dp_ctrl_enable_mainlink_clocks(struct dp_ctrl_private
*ctrl, unsigned long pixel_rate)
 {
 	int ret = 0;
 	struct dp_io *dp_io = &ctrl->parser->io;
@@ -1359,25 +1357,25 @@ static int
dp_ctrl_enable_mainlink_clocks(struct dp_ctrl_private *ctrl)
 	if (ret)
 		DRM_ERROR("Unable to start link clocks. ret=%d\n", ret);

-	drm_dbg_dp(ctrl->drm_dev, "link rate=%d pixel_clk=%d\n",
-		ctrl->link->link_params.rate, ctrl->dp_ctrl.pixel_rate);
+	drm_dbg_dp(ctrl->drm_dev, "link rate=%d pixel_clk=%lu\n",
+		ctrl->link->link_params.rate, pixel_rate);

 	return ret;
 }

-static int dp_ctrl_enable_stream_clocks(struct dp_ctrl_private *ctrl)
+static int dp_ctrl_enable_stream_clocks(struct dp_ctrl_private *ctrl,
+					unsigned long pixel_rate)
 {
-	int ret = 0;
+	int ret;

-	dp_ctrl_set_clock_rate(ctrl, DP_STREAM_PM, "stream_pixel",
-					ctrl->dp_ctrl.pixel_rate * 1000);
+	dp_ctrl_set_clock_rate(ctrl, DP_STREAM_PM, "stream_pixel", pixel_rate * 1000);

 	ret = dp_power_clk_enable(ctrl->power, DP_STREAM_PM, true);
 	if (ret)
 		DRM_ERROR("Unabled to start pixel clocks. ret=%d\n", ret);

-	drm_dbg_dp(ctrl->drm_dev, "link rate=%d pixel_clk=%d\n",
-			ctrl->link->link_params.rate, ctrl->dp_ctrl.pixel_rate);
+	drm_dbg_dp(ctrl->drm_dev, "link rate=%d pixel_clk=%lu\n",
+			ctrl->link->link_params.rate, pixel_rate);

 	return ret;
 }
@@ -1447,7 +1445,7 @@ static bool dp_ctrl_use_fixed_nvid(struct
dp_ctrl_private *ctrl)
 	return false;
 }

-static int dp_ctrl_reinitialize_mainlink(struct dp_ctrl_private *ctrl)
+static int dp_ctrl_reinitialize_mainlink(struct dp_ctrl_private
*ctrl, unsigned long pixel_rate)
 {
 	int ret = 0;
 	struct dp_io *dp_io = &ctrl->parser->io;
@@ -1471,7 +1469,7 @@ static int dp_ctrl_reinitialize_mainlink(struct
dp_ctrl_private *ctrl)
 	/* hw recommended delay before re-enabling clocks */
 	msleep(20);

-	ret = dp_ctrl_enable_mainlink_clocks(ctrl);
+	ret = dp_ctrl_enable_mainlink_clocks(ctrl, pixel_rate);
 	if (ret) {
 		DRM_ERROR("Failed to enable mainlink clks. ret=%d\n", ret);
 		return ret;
@@ -1519,8 +1517,6 @@ static int dp_ctrl_link_maintenance(struct
dp_ctrl_private *ctrl)
 	ctrl->link->phy_params.p_level = 0;
 	ctrl->link->phy_params.v_level = 0;

-	ctrl->dp_ctrl.pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;
-
 	ret = dp_ctrl_setup_main_link(ctrl, &training_step);
 	if (ret)
 		goto end;
@@ -1534,36 +1530,6 @@ static int dp_ctrl_link_maintenance(struct
dp_ctrl_private *ctrl)
 	return ret;
 }

-static int dp_ctrl_process_phy_test_request(struct dp_ctrl_private *ctrl)
-{
-	int ret = 0;
-
-	if (!ctrl->link->phy_params.phy_test_pattern_sel) {
-		drm_dbg_dp(ctrl->drm_dev,
-			"no test pattern selected by sink\n");
-		return ret;
-	}
-
-	/*
-	 * The global reset will need DP link related clocks to be
-	 * running. Add the global reset just before disabling the
-	 * link clocks and core clocks.
-	 */
-	ret = dp_ctrl_off(&ctrl->dp_ctrl);
-	if (ret) {
-		DRM_ERROR("failed to disable DP controller\n");
-		return ret;
-	}
-
-	ret = dp_ctrl_on_link(&ctrl->dp_ctrl);
-	if (!ret)
-		ret = dp_ctrl_on_stream_phy_test_report(&ctrl->dp_ctrl);
-	else
-		DRM_ERROR("failed to enable DP link controller\n");
-
-	return ret;
-}
-
 static bool dp_ctrl_send_phy_test_pattern(struct dp_ctrl_private *ctrl)
 {
 	bool success = false;
@@ -1616,6 +1582,56 @@ static bool
dp_ctrl_send_phy_test_pattern(struct dp_ctrl_private *ctrl)
 	return success;
 }

+static int dp_ctrl_on_stream_phy_test_report(struct dp_ctrl *dp_ctrl)
+{
+	int ret;
+	struct dp_ctrl_private *ctrl;
+	unsigned long pixel_rate;
+
+	ctrl = container_of(dp_ctrl, struct dp_ctrl_private, dp_ctrl);
+
+	pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;
+	ret = dp_ctrl_enable_stream_clocks(ctrl, pixel_rate);
+	if (ret) {
+		DRM_ERROR("Failed to start pixel clocks. ret=%d\n", ret);
+		return ret;
+	}
+
+	dp_ctrl_send_phy_test_pattern(ctrl);
+
+	return 0;
+}
+
+static int dp_ctrl_process_phy_test_request(struct dp_ctrl_private *ctrl)
+{
+	int ret = 0;
+
+	if (!ctrl->link->phy_params.phy_test_pattern_sel) {
+		drm_dbg_dp(ctrl->drm_dev,
+			"no test pattern selected by sink\n");
+		return ret;
+	}
+
+	/*
+	 * The global reset will need DP link related clocks to be
+	 * running. Add the global reset just before disabling the
+	 * link clocks and core clocks.
+	 */
+	ret = dp_ctrl_off(&ctrl->dp_ctrl);
+	if (ret) {
+		DRM_ERROR("failed to disable DP controller\n");
+		return ret;
+	}
+
+	ret = dp_ctrl_on_link(&ctrl->dp_ctrl);
+	if (!ret)
+		ret = dp_ctrl_on_stream_phy_test_report(&ctrl->dp_ctrl);
+	else
+		DRM_ERROR("failed to enable DP link controller\n");
+
+	return ret;
+}
+
 void dp_ctrl_handle_sink_request(struct dp_ctrl *dp_ctrl)
 {
 	struct dp_ctrl_private *ctrl;
@@ -1691,6 +1707,7 @@ int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
 	u32 const phy_cts_pixel_clk_khz = 148500;
 	u8 link_status[DP_LINK_STATUS_SIZE];
 	unsigned int training_step;
+	unsigned long pixel_rate;

 	if (!dp_ctrl)
 		return -EINVAL;
@@ -1705,25 +1722,25 @@ int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
 		drm_dbg_dp(ctrl->drm_dev,
 				"using phy test link parameters\n");
 		if (!ctrl->panel->dp_mode.drm_mode.clock)
-			ctrl->dp_ctrl.pixel_rate = phy_cts_pixel_clk_khz;
+			pixel_rate = phy_cts_pixel_clk_khz;
 	} else {
 		ctrl->link->link_params.rate = rate;
 		ctrl->link->link_params.num_lanes =
 			ctrl->panel->link_info.num_lanes;
-		ctrl->dp_ctrl.pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;
+		pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;
 	}

-	drm_dbg_dp(ctrl->drm_dev, "rate=%d, num_lanes=%d, pixel_rate=%d\n",
+	drm_dbg_dp(ctrl->drm_dev, "rate=%d, num_lanes=%d, pixel_rate=%lu\n",
 		ctrl->link->link_params.rate, ctrl->link->link_params.num_lanes,
-		ctrl->dp_ctrl.pixel_rate);
+		pixel_rate);


-	rc = dp_ctrl_enable_mainlink_clocks(ctrl);
+	rc = dp_ctrl_enable_mainlink_clocks(ctrl, pixel_rate);
 	if (rc)
 		return rc;

 	while (--link_train_max_retries) {
-		rc = dp_ctrl_reinitialize_mainlink(ctrl);
+		rc = dp_ctrl_reinitialize_mainlink(ctrl, pixel_rate);
 		if (rc) {
 			DRM_ERROR("Failed to reinitialize mainlink. rc=%d\n",
 					rc);
@@ -1813,31 +1830,12 @@ static int dp_ctrl_link_retrain(struct
dp_ctrl_private *ctrl)
 	return dp_ctrl_setup_main_link(ctrl, &training_step);
 }

-int dp_ctrl_on_stream_phy_test_report(struct dp_ctrl *dp_ctrl)
-{
-	int ret;
-	struct dp_ctrl_private *ctrl;
-
-	ctrl = container_of(dp_ctrl, struct dp_ctrl_private, dp_ctrl);
-
-	ctrl->dp_ctrl.pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;
-
-	ret = dp_ctrl_enable_stream_clocks(ctrl);
-	if (ret) {
-		DRM_ERROR("Failed to start pixel clocks. ret=%d\n", ret);
-		return ret;
-	}
-
-	dp_ctrl_send_phy_test_pattern(ctrl);
-
-	return 0;
-}
-
 int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl, bool force_link_train)
 {
 	int ret = 0;
 	bool mainlink_ready = false;
 	struct dp_ctrl_private *ctrl;
+	unsigned long pixel_rate;
 	unsigned long pixel_rate_orig;

 	if (!dp_ctrl)
@@ -1845,25 +1843,24 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl,
bool force_link_train)

 	ctrl = container_of(dp_ctrl, struct dp_ctrl_private, dp_ctrl);

-	ctrl->dp_ctrl.pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;
+	pixel_rate = pixel_rate_orig = ctrl->panel->dp_mode.drm_mode.clock;

-	pixel_rate_orig = ctrl->dp_ctrl.pixel_rate;
 	if (dp_ctrl->wide_bus_en)
-		ctrl->dp_ctrl.pixel_rate >>= 1;
+		pixel_rate >>= 1;

-	drm_dbg_dp(ctrl->drm_dev, "rate=%d, num_lanes=%d, pixel_rate=%d\n",
+	drm_dbg_dp(ctrl->drm_dev, "rate=%d, num_lanes=%d, pixel_rate=%lu\n",
 		ctrl->link->link_params.rate,
-		ctrl->link->link_params.num_lanes, ctrl->dp_ctrl.pixel_rate);
+		ctrl->link->link_params.num_lanes, pixel_rate);

 	if (!dp_power_clk_status(ctrl->power, DP_CTRL_PM)) { /* link clk is off */
-		ret = dp_ctrl_enable_mainlink_clocks(ctrl);
+		ret = dp_ctrl_enable_mainlink_clocks(ctrl, pixel_rate);
 		if (ret) {
 			DRM_ERROR("Failed to start link clocks. ret=%d\n", ret);
 			goto end;
 		}
 	}

-	ret = dp_ctrl_enable_stream_clocks(ctrl);
+	ret = dp_ctrl_enable_stream_clocks(ctrl, pixel_rate);
 	if (ret) {
 		DRM_ERROR("Failed to start pixel clocks. ret=%d\n", ret);
 		goto end;
diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.h b/drivers/gpu/drm/msm/dp/dp_ctrl.h
index 9a39b0089ae0..9f29734af81c 100644
--- a/drivers/gpu/drm/msm/dp/dp_ctrl.h
+++ b/drivers/gpu/drm/msm/dp/dp_ctrl.h
@@ -16,13 +16,11 @@
 struct dp_ctrl {
 	bool orientation;
 	atomic_t aborted;
-	u32 pixel_rate;
 	bool wide_bus_en;
 };

 int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl);
 int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl, bool force_link_train);
-int dp_ctrl_on_stream_phy_test_report(struct dp_ctrl *dp_ctrl);
 int dp_ctrl_off_link_stream(struct dp_ctrl *dp_ctrl);
 int dp_ctrl_off_link(struct dp_ctrl *dp_ctrl);
 int dp_ctrl_off(struct dp_ctrl *dp_ctrl);