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

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Message-ID: <20250117091213.647bf0e6@bootlin.com>
Date: Fri, 17 Jan 2025 09:12:13 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Maxime Ripard <mripard@...nel.org>
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

Hi Maxime,

On Thu, 16 Jan 2025 09:38:45 +0100
Maxime Ripard <mripard@...nel.org> wrote:

> 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/

Thanks for pointing that, indeed, it clarify many things!

> 
> > 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.

Yes, I agree with that, I only need the active CRTC.

I tried to get the current atomic_state from:
  1) bridge->base.state->state
  2) drm_bridge_state->base.state

In both cases, it is NULL. Looking at Sima's reply in your series
explained that:
  https://lore.kernel.org/dri-devel/Z4juJy7kKPbI2BDb@phenom.ffwll.local/

If I understood correctly those pointers are explicitly cleared.

So, with all of that, either:
  a) I wait for your series to be applied in order to use your the crtc field from
     drm_bridge_state added by:
       https://lore.kernel.org/dri-devel/20250115-bridge-connector-v1-25-9a2fecd886a6@kernel.org/#t
  b) I use the old school bridge->encoder->crtc for the moment

Do you mind if I use the bridge->encoder->crtc way for the next iteration of
my series?

Best regards,
Hervé