linux-kernel - Re: [PATCH v3] drm/msm/dp: call dp_hpd_plug_handle()/unplug

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Date: Sun, 7 Apr 2024 05:03:48 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc: freedreno@...ts.freedesktop.org, Rob Clark <robdclark@...il.com>, 
	Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Bjorn Andersson <andersson@...nel.org>, Kuogee Hsieh <quic_khsieh@...cinc.com>, 
	dri-devel@...ts.freedesktop.org, seanpaul@...omium.org, swboyd@...omium.org, 
	quic_jesszhan@...cinc.com, quic_bjorande@...cinc.com, johan@...nel.org, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] drm/msm/dp: call dp_hpd_plug_handle()/unplug_handle()
 directly for external HPD

On Sat, 6 Apr 2024 at 06:16, Abhinav Kumar <quic_abhinavk@...cinc.com> wrote:
>
> From: Kuogee Hsieh <quic_khsieh@...cinc.com>
>
> For HPD events coming from external modules using drm_bridge_hpd_notify(),
> the sequence of calls leading to dp_bridge_hpd_notify() is like below:
>
> dp_bridge_hpd_notify+0x18/0x70 [msm]
> drm_bridge_connector_detect+0x60/0xe8 [drm_kms_helper]
> drm_helper_probe_detect+0x94/0xc0 [drm_kms_helper]
> drm_helper_probe_single_connector_modes+0x43c/0x53c [drm_kms_helper]
> drm_client_modeset_probe+0x240/0x1114 [drm]
> drm_fb_helper_hotplug_event.part.26+0x9c/0xe8 [drm_kms_helper]
> drm_fb_helper_hotplug_event+0x24/0x38 [drm_kms_helper]
> msm_fbdev_client_hotplug+0x24/0xd4 [msm]
> drm_client_dev_hotplug+0xd8/0x148 [drm]
> drm_kms_helper_connector_hotplug_event+0x30/0x3c [drm_kms_helper]
> drm_bridge_connector_handle_hpd+0x84/0x94 [drm_kms_helper]
> drm_bridge_connector_hpd_cb+0xc/0x14 [drm_kms_helper]
> drm_bridge_hpd_notify+0x38/0x50 [drm]
> drm_aux_hpd_bridge_notify+0x14/0x20 [aux_hpd_bridge]
> pmic_glink_altmode_worker+0xec/0x27c [pmic_glink_altmode]
> process_scheduled_works+0x17c/0x2cc
> worker_thread+0x2ac/0x2d0
> kthread+0xfc/0x120
>
> There are three notifications delivered to DP driver for each notification event.
>
> 1) From the drm_aux_hpd_bridge_notify() itself as shown above
>
> 2) From output_poll_execute() thread which arises due to
> drm_helper_probe_single_connector_modes() call of the above stacktrace
> as shown in more detail here.
>
> dp_bridge_hpd_notify+0x18/0x70 [msm]
> drm_bridge_connector_detect+0x60/0xe8 [drm_kms_helper]
> drm_helper_probe_detect+0x94/0xc0 [drm_kms_helper]
> drm_helper_probe_single_connector_modes+0x43c/0x53c [drm_kms_helper]
> drm_client_modeset_probe+0x240/0x1114 [drm]
> drm_fb_helper_hotplug_event.part.26+0x9c/0xe8 [drm_kms_helper]
> drm_fb_helper_hotplug_event+0x24/0x38 [drm_kms_helper]
> msm_fbdev_client_hotplug+0x24/0xd4 [msm]
> drm_client_dev_hotplug+0xd8/0x148 [drm]
> drm_kms_helper_hotplug_event+0x30/0x3c [drm_kms_helper]
> output_poll_execute+0xe0/0x210 [drm_kms_helper]
>
> 3) From the DP driver as the dp_bridge_hpd_notify() callback today triggers
> the hpd_event_thread for connect and disconnect events respectively via below stack
>
> dp_bridge_hpd_notify+0x18/0x70 [msm]
> drm_bridge_connector_detect+0x60/0xe8 [drm_kms_helper]
> drm_helper_probe_detect_ctx+0x98/0x110 [drm_kms_helper]
> check_connector_changed+0x4c/0x20c [drm_kms_helper]
> drm_helper_hpd_irq_event+0x98/0x120 [drm_kms_helper]
> hpd_event_thread+0x478/0x5bc [msm]
>
> dp_bridge_hpd_notify() delivered from output_poll_execute() thread
> returns the incorrect HPD status as the MSM DP driver returns the value
> of link_ready and not the HPD status currently in the .detect() callback.
>
> And because the HPD event thread has not run yet, this results in two complementary
> events.
>
> To address this, fix dp_bridge_hpd_notify() to call dp_hpd_plug_handle/unplug_handle()
> directly to return consistent values for the above scenarios.
>
> changes in v3:
>         - Fix the commit message as per submitting guidelines.
>         - remove extra line added
>
> changes in v2:
>         - Fix the commit message to explain the scenario
>         - Fix the subject a little as well
>
> Fixes: 542b37efc20e ("drm/msm/dp: Implement hpd_notify()")
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_display.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

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

-- 
With best wishes
Dmitry