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

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Message-ID: <20241029-raspberry-ferret-of-advertising-1f4c4d@houat>
Date: Tue, 29 Oct 2024 09:28:18 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Andy Yan <andyshrk@....com>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
	Herve Codina <herve.codina@...tlin.com>, Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 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, 
	Luca Ceresoli <luca.ceresoli@...tlin.com>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 2/2] drm: bridge: ti-sn65dsi83: Add error recovery
 mechanism

On Tue, Oct 29, 2024 at 04:02:33PM +0800, Andy Yan wrote:
> At 2024-10-28 00:23:50, "Laurent Pinchart" <laurent.pinchart@...asonboard.com> wrote:
> >On Thu, Oct 24, 2024 at 11:55:38AM +0200, Herve Codina wrote:
> >> In some cases observed during ESD tests, the TI SN65DSI83 cannot recover
> >> from errors by itself. A full restart of the bridge is needed in those
> >> cases to have the bridge output LVDS signals again.
> >> 
> >> The TI SN65DSI83 has some error detection capabilities. Introduce an
> >> error recovery mechanism based on this detection.
> >> 
> >> The errors detected are signaled through an interrupt. On system where
> >> this interrupt is not available, the driver uses a polling monitoring
> >> fallback to check for errors. When an error is present, the recovery
> >> process is launched.
> >> 
> >> Restarting the bridge needs to redo the initialization sequence. This
> >> initialization sequence has to be done with the DSI data lanes driven in
> >> LP11 state. In order to do that, the recovery process resets the entire
> >> pipeline.
> >> 
> >> Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> >> ---
> >>  drivers/gpu/drm/bridge/ti-sn65dsi83.c | 128 ++++++++++++++++++++++++++
> >>  1 file changed, 128 insertions(+)
> >> 
> >> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> >> index 96e829163d87..22975b60e80f 100644
> >> --- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> >> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> >> @@ -35,9 +35,12 @@
> >>  #include <linux/of_graph.h>
> >>  #include <linux/regmap.h>
> >>  #include <linux/regulator/consumer.h>
> >> +#include <linux/timer.h>
> >> +#include <linux/workqueue.h>
> >>  
> >>  #include <drm/drm_atomic_helper.h>
> >>  #include <drm/drm_bridge.h>
> >> +#include <drm/drm_drv.h> /* DRM_MODESET_LOCK_ALL_BEGIN() need drm_drv_uses_atomic_modeset() */
> >>  #include <drm/drm_mipi_dsi.h>
> >>  #include <drm/drm_of.h>
> >>  #include <drm/drm_panel.h>
> >> @@ -147,6 +150,9 @@ struct sn65dsi83 {
> >>  	struct regulator		*vcc;
> >>  	bool				lvds_dual_link;
> >>  	bool				lvds_dual_link_even_odd_swap;
> >> +	bool				use_irq;
> >> +	struct delayed_work		monitor_work;
> >> +	struct work_struct		reset_work;
> >>  };
> >>  
> >>  static const struct regmap_range sn65dsi83_readable_ranges[] = {
> >> @@ -321,6 +327,92 @@ static u8 sn65dsi83_get_dsi_div(struct sn65dsi83 *ctx)
> >>  	return dsi_div - 1;
> >>  }
> >>  
> >> +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 ?
> 
> If we could simulate a hotplug（disconnected then connected） event to
> user space and let userspace do the disable/enable of the output
> pipeline, would things be simpler?

No, because you can't expect the userspace to handle that event in the
first place.

Maxime

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