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Date: Fri, 3 Jun 2022 14:31:09 -0700
From: Kuogee Hsieh <quic_khsieh@...cinc.com>
To: <robdclark@...il.com>, <sean@...rly.run>, <swboyd@...omium.org>,
<dianders@...omium.org>, <vkoul@...nel.org>, <daniel@...ll.ch>,
<airlied@...ux.ie>, <agross@...nel.org>,
<dmitry.baryshkov@...aro.org>, <bjorn.andersson@...aro.org>
CC: <quic_abhinavk@...cinc.com>, <quic_aravindh@...cinc.com>,
<quic_sbillaka@...cinc.com>, <freedreno@...ts.freedesktop.org>,
<dri-devel@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] drm/msm/dp: force link training for display resolution
change
Any one has any comments?
Thanks,
On 5/27/2022 2:32 PM, Kuogee Hsieh wrote:
> During display resolution changes display have to be disabled first
> followed by display enabling with new resolution. 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. Main link retraining will not be executed by
> irq_hdp_handle() if the link status read from pane shows it is in
> sync state. If this was happen, then 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 force main link always
> be retrained during display enable procedure to prevent this rare
> failed case from happening. 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
>
> Fixes: 62671d2ef24b ("drm/msm/dp: fixes wrong connection state caused by failure of link train")
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---
> drivers/gpu/drm/msm/dp/dp_ctrl.c | 6 +++---
> drivers/gpu/drm/msm/dp/dp_ctrl.h | 2 +-
> drivers/gpu/drm/msm/dp/dp_display.c | 15 ++++++++-------
> 3 files changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index af7a80c..bea93eb 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(&ctrl->dp_ctrl, false);
> else
> DRM_ERROR("failed to enable DP link controller\n");
>
> @@ -1807,7 +1807,7 @@ 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(struct dp_ctrl *dp_ctrl, bool force_link_train)
> {
> int ret = 0;
> bool mainlink_ready = false;
> @@ -1848,7 +1848,7 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_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..b563e2e 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.h
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.h
> @@ -21,7 +21,7 @@ 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_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..370348d 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 +1689,14 @@ 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);
>
> - dp_display_enable(dp_display, 0);
> + if (!dp->is_edp)
> + force_link_train = true;
> + }
> +
> + dp_display_enable(dp_display, force_link_train);
>
> rc = dp_display_post_enable(dp);
> if (rc) {
> @@ -1700,10 +1705,6 @@ void dp_bridge_enable(struct drm_bridge *drm_bridge)
> dp_display_unprepare(dp);
> }
>
> - /* manual kick off plug event to train link */
> - if (state == ST_DISPLAY_OFF)
> - dp_add_event(dp_display, EV_IRQ_HPD_INT, 0, 0);
> -
> /* completed connection */
> dp_display->hpd_state = ST_CONNECTED;
>
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