[PATCH 2/2] drm: bridge: ti-sn65dsi83: Add error recovery mechanism

[Maxime Ripard]

On Mon, Oct 28, 2024 at 01:28:57PM +0200, Laurent Pinchart wrote:
> On Mon, Oct 28, 2024 at 09:13:31AM +0100, Herve Codina wrote:
> > Hi Laurent,
> > 
> > On Sun, 27 Oct 2024 18:23:50 +0200
> > Laurent Pinchart <laurent.pinchart at ideasonboard.com> wrote:
> > 
> > [...]
> > > > +static int sn65dsi83_reset_pipeline(struct sn65dsi83 *sn65dsi83)
> > > > +{
> > > > +	struct drm_device *dev = sn65dsi83->bridge.dev;
> > > > +	struct drm_modeset_acquire_ctx ctx;
> > > > +	struct drm_atomic_state *state;
> > > > +	int err;
> > > > +
> > > > +	/* Use operation done in drm_atomic_helper_suspend() followed by
> > > > +	 * operation done in drm_atomic_helper_resume() but without releasing
> > > > +	 * the lock between suspend()/resume()
> > > > +	 */
> > > > +
> > > > +	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;
> > > > +	}
> > > > +
> > > > +	err = drm_atomic_helper_disable_all(dev, &ctx);
> > > > +	if (err < 0)
> > > > +		goto unlock;
> > > > +
> > > > +	drm_mode_config_reset(dev);
> > > > +
> > > > +	err = drm_atomic_helper_commit_duplicated_state(state, &ctx);  
> > > 
> > > Committing a full atomic state from a bridge driver in an asynchronous
> > > way seems quite uncharted territory, and it worries me. It's also a very
> > > heavyweight, you disable all outputs here, instead of focussing on the
> > > output connected to the bridge. Can you either implement something more
> > > local, resetting the bridge only, or create a core helper to handle this
> > > kind of situation, on a per-output basis ?
> > 
> > A full restart of the bridge (power off/on) is needed and so we need to
> > redo the initialization sequence. This initialization sequence has to be
> > done with the DSI data lanes (bridge inputs) driven in LP11 state and so
> > without any video stream. Only focussing on bridge outputs will not be
> > sufficient. That's why I brought the pipeline down and restarted it.
> 
> Fair point.
> 
> > Of course, I can copy/paste sn65dsi83_reset_pipeline() to a core helper
> > function. Is drm_atomic_helper_reset_all() could be a good candidate?
> 
> The helper should operate on a single output, unrelated outputs should
> not be affected.

Also, you don't want to reset anything, you just want the last commit to
be replayed.

Maxime
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