linux-kernel - Re: [PATCH v4 24/25] drm/msm/dpu: Reorder encoder kickoff for CWB

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Message-ID: <dszctcu5mm4hudc53gqpjklcugah5lisvvfkbmejeywgceqyl5@dqzopvt2lb7s>
Date: Fri, 20 Dec 2024 08:00:26 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Jessica Zhang <quic_jesszhan@...cinc.com>
Cc: Rob Clark <robdclark@...il.com>, quic_abhinavk@...cinc.com, 
	Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>, 
	David Airlie <airlied@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	Simona Vetter <simona@...ll.ch>, Simona Vetter <simona.vetter@...ll.ch>, 
	quic_ebharadw@...cinc.com, linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org, Rob Clark <robdclark@...omium.org>, 
	Ville Syrjälä <ville.syrjala@...ux.intel.com>
Subject: Re: [PATCH v4 24/25] drm/msm/dpu: Reorder encoder kickoff for CWB

On Mon, Dec 16, 2024 at 04:43:35PM -0800, Jessica Zhang wrote:
> Add a helper that will handle the correct order of the encoder kickoffs
> for concurrent writeback.
> 
> For concurrent writeback, the realtime encoder must always kickoff last
> as it will call the trigger flush and start.
> 
> This avoids the following scenario where the writeback encoder
> increments the pending kickoff count after the WB_DONE interrupt is
> fired:
> 
> If the realtime encoder is kicked off first, the encoder kickoff will
> flush/start the encoder and increment the pending kickoff count. The
> WB_DONE interrupt then fires (before the writeback encoder is kicked
> off). When the writeback encoder enters its kickoff, it will skip the
> flush/start (due to CWB being enabled) and hit a frame done timeout
> as the frame was kicked off (and the WB_DONE interrupt fired) without
> the pending kickoff count being incremented.
> 
> In addition, the writeback timer should only start after the realtime
> encoder is kicked off to ensure that we don't get timeouts when the
> system has a heavy load (ex. when debug logs are enabled)
> 
> Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 74 ++++++++++++++++++++++++++------
>  1 file changed, 60 insertions(+), 14 deletions(-)

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

-- 
With best wishes
Dmitry