linux-kernel - Re: [RFC PATCH] drm: allow encoder mode_set even when connectors change for crtc

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Message-ID: <20240909-neat-stoic-hamster-cbbe42@houat>
Date: Mon, 9 Sep 2024 15:37:52 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc: dri-devel@...ts.freedesktop.org, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, linux-arm-msm@...r.kernel.org, 
	freedreno@...ts.freedesktop.org, robdclark@...il.com, dmitry.baryshkov@...aro.org, 
	quic_jesszhan@...cinc.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] drm: allow encoder mode_set even when connectors
 change for crtc

Hi,

On Thu, Sep 05, 2024 at 03:11:24PM GMT, Abhinav Kumar wrote:
> In certain use-cases, a CRTC could switch between two encoders
> and because the mode being programmed on the CRTC remains
> the same during this switch, the CRTC's mode_changed remains false.
> In such cases, the encoder's mode_set also gets skipped.
> 
> Skipping mode_set on the encoder for such cases could cause an issue
> because even though the same CRTC mode was being used, the encoder
> type could have changed like the CRTC could have switched from a
> real time encoder to a writeback encoder OR vice-versa.
> 
> Allow encoder's mode_set to happen even when connectors changed on a
> CRTC and not just when the mode changed.
> 
> Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>

The patch and rationale looks sane to me, but we should really add kunit
tests for that scenarii.

Maxime

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