linux-kernel - Re: [PATCH v3 3/3] drm: bridge: ti-sn65dsi83: Add error recovery mechanism

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Message-ID: <20250116-archetypal-bulldog-of-expression-fcc937@houat>
Date: Thu, 16 Jan 2025 09:38:45 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Herve Codina <herve.codina@...tlin.com>
Cc: 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>, 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 v3 3/3] drm: bridge: ti-sn65dsi83: Add error recovery
 mechanism

On Tue, Jan 14, 2025 at 01:54:56PM +0100, Herve Codina wrote:
> Hi Maxime,
> 
> On Tue, 14 Jan 2025 08:40:51 +0100
> Maxime Ripard <mripard@...nel.org> wrote:
> 
> ...
> 
> > >  
> > > +static int sn65dsi83_reset_pipe(struct sn65dsi83 *sn65dsi83)
> > > +{
> > > +	struct drm_atomic_state *state = ERR_PTR(-EINVAL);
> > > +	struct drm_device *dev = sn65dsi83->bridge.dev;
> > > +	struct drm_connector_state *connector_state;
> > > +	struct drm_modeset_acquire_ctx ctx;
> > > +	struct drm_connector *connector;
> > > +	int err;
> > > +
> > > +	/*
> > > +	 * Reset active outputs of the related CRTC.
> > > +	 *
> > > +	 * This way, drm core will reconfigure each components in the CRTC
> > > +	 * outputs path. In our case, this will force the previous component to
> > > +	 * go back in LP11 mode and so allow the reconfiguration of SN64DSI83
> > > +	 * bridge.
> > > +	 *
> > > +	 * Keep the lock during the whole operation to be atomic.
> > > +	 */
> > > +
> > > +	DRM_MODESET_LOCK_ALL_BEGIN(dev, ctx, 0, err);
> > > +
> > > +	state = drm_atomic_helper_duplicate_state(dev, &ctx);
> > > +	if (IS_ERR(state)) {
> > > +		err = PTR_ERR(state);
> > > +		goto unlock;
> > > +	}  
> > 
> > No, you must not allocate a new state for this, you need to reuse the
> > existing state. You'll find it in bridge->base.state->state.
> 
> Thanks for pointing that. I didn't know about bridge->base.state->state.
> 
> I will use that if using the state is still relevant (see next comment).
> 
> > 
> > > +	state->acquire_ctx = &ctx;
> > > +
> > > +	connector = drm_atomic_get_old_connector_for_encoder(state,
> > > +							     sn65dsi83->bridge.encoder);
> > > +	if (!connector) {
> > > +		err = -EINVAL;
> > > +		goto unlock;
> > > +	}
> > > +
> > > +	connector_state = drm_atomic_get_connector_state(state, connector);
> > > +	if (IS_ERR(connector_state)) {
> > > +		err = PTR_ERR(connector_state);
> > > +		goto unlock;
> > > +	}
> > > +
> > > +	err = drm_atomic_helper_reset_pipe(connector_state->crtc, &ctx);
> > > +	if (err < 0)
> > > +		goto unlock;  
> > 
> > And you'll find the crtc in bridge->encoder->crtc.
> 
> I am a bit confused. I looked at the drm_encoder structure [1] and the crtc
> field available in this structure should not be used by atomic drivers. They
> should rely on &drm_connector_state.crtc.

You're right, it's deprecated but used by most bridges anyway.

I made a series of changes after reviewing your series to address some
issues with the current bridge API, most notably

https://lore.kernel.org/dri-devel/20250115-bridge-connector-v1-25-9a2fecd886a6@kernel.org/

> In my case, I have the feeling that I should get the ctrc from the current
> state (i.e. bridge->base.state->state) using the sequence provided in this
> current patch:
>   Retrieve the connector with drm_atomic_get_old_connector_for_encoder()

Retrieving the old connector makes no sense though. It's the connector
that was formerly associated with your encoder. It might work, it might
not, it's not what you're looking for.

>   Retrieve the connector state with drm_atomic_get_connector_state()

drm_atomic_get_connector_state will allocate and pull the connector
state into the drm_atomic_state, even if it wasn't part of it before, so
it's not great. And you don't need it in the first place, you only need
the current active CRTC.

> but you pointed out the bridge->encoder->crtc field.
>
> Should I use this field or use the &drm_connector_state.crtc with the drm
> connector state retrieved from bridge->base.state->state using the proposed
> sequence?

Having access to the connector isn't really easy either. Hopefully that
patch above should help there.

Maxime

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