linux-kernel - Re: [PATCH v4 2/4] drm/atomic-helper: Introduce drm_atomic_helper_reset

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Message-ID: <20250220-wooden-robin-of-discussion-6a36f1@houat>
Date: Thu, 20 Feb 2025 11:44:37 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Herve Codina <herve.codina@...tlin.com>, 
	Alexander Stein <alexander.stein@...tq-group.com>, Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Dave Stevenson <dave.stevenson@...pberrypi.com>, Maíra Canal <mcanal@...lia.com>, 
	Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>, Marek Vasut <marex@...x.de>, dri-devel@...ts.freedesktop.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Louis Chauvet <louis.chauvet@...tlin.com>, Luca Ceresoli <luca.ceresoli@...tlin.com>, 
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v4 2/4] drm/atomic-helper: Introduce
 drm_atomic_helper_reset_crtc()

On Wed, Feb 19, 2025 at 02:41:48PM +0100, Simona Vetter wrote:
> On Mon, Feb 03, 2025 at 03:58:21PM +0100, Herve Codina wrote:
> > drm_atomic_helper_reset_crtc() allows to reset the CRTC active outputs.
> > 
> > This resets all active components available between the CRTC and
> > connectors.
> > 
> > Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> > ---
> >  drivers/gpu/drm/drm_atomic_helper.c | 41 +++++++++++++++++++++++++++++
> >  include/drm/drm_atomic_helper.h     |  2 ++
> >  2 files changed, 43 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index 8ed186ddaeaf..cac807df8a86 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -3363,6 +3363,47 @@ int drm_atomic_helper_disable_all(struct drm_device *dev,
> >  }
> >  EXPORT_SYMBOL(drm_atomic_helper_disable_all);
> >  
> > +/**
> > + * drm_atomic_helper_reset_crtc - reset the active outputs of a CRTC
> > + * @crtc: DRM CRTC
> > + * @ctx: lock acquisition context
> > + *
> > + * Reset the active outputs by indicating that connectors have changed.
> > + * This implies a reset of all active components available between the CRTC and
> > + * connectors.
> 
> I think you definitely want a
> 
> 	Note: This relies on resetting &drm_crtc_state.connectors_changed.
> 	For drivers which optimize out unnecessary modesets this will
> 	result in a no-op commit, achieving nothing.
> 
> > + *
> > + * Returns:
> > + * 0 on success or a negative error code on failure.
> > + */
> > +int drm_atomic_helper_reset_crtc(struct drm_crtc *crtc,
> > +				 struct drm_modeset_acquire_ctx *ctx)
> 
> So this is pretty close to DP drivers doing link-retraining when
> reconnecting a cable. Would be really nice if that could also be rolled
> out there where it fits, and maybe augment the documentation accordingly
> so that dp helpers point at this?

Given that the patch is already merged, Herve, could you send a
subsequent patch fixing up the doc at least?

Thanks,
Maxime

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