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

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Message-ID: <20250109121808.1cad0c1f@bootlin.com>
Date: Thu, 9 Jan 2025 12:18:08 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Alexander Stein <alexander.stein@...tq-group.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>, Maxime Ripard <mripard@...nel.org>,
 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 Thu, 09 Jan 2025 11:49:13 +0100
Alexander Stein <alexander.stein@...tq-group.com> wrote:

> Hi Herve,
> 
> Am Mittwoch, 8. Januar 2025, 18:44:42 CET schrieb Herve Codina:
> > Hi Alexander,
> > 
> > On Wed, 08 Jan 2025 11:54:49 +0100
> > Alexander Stein <alexander.stein@...tq-group.com> wrote:
> > 
> > [...]  
> > > >  #include <drm/drm_atomic_helper.h>
> > > >  #include <drm/drm_bridge.h>
> > > > +#include <drm/drm_drv.h> /* DRM_MODESET_LOCK_ALL_BEGIN() needs drm_drv_uses_atomic_modeset() */    
> > > 
> > > Shouldn't this include be added to include/drm/drm_modeset_lock.h instead?  
> > 
> > Yes indeed. I will change that in the next iteration.
> >   
> > >   
> > > >  #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;    
> > > 
> > > Can you please rebase? You are missing commit d2b8c6d549570
> > > ("drm/bridge: ti-sn65dsi83: Add ti,lvds-vod-swing optional properties")  
> > 
> > Sure, I will rebase.
> > 
> > [...]  
> > > > +static void sn65dsi83_handle_errors(struct sn65dsi83 *ctx)
> > > > +{
> > > > +	unsigned int irq_stat;
> > > > +	int ret;
> > > > +
> > > > +	/*
> > > > +	 * Schedule a reset in case of:
> > > > +	 *  - the bridge doesn't answer
> > > > +	 *  - the bridge signals an error
> > > > +	 */
> > > > +
> > > > +	ret = regmap_read(ctx->regmap, REG_IRQ_STAT, &irq_stat);
> > > > +	if (ret || irq_stat)
> > > > +		schedule_work(&ctx->reset_work);    
> > > 
> > > Shouldn't you clear the error bits as well?  
> > 
> > Thanks for pointing that.
> > 
> > I can clear the error bit but further more, I probably need to simply
> > disable the interrupt.
> > 
> > In some cases, we observed i2c access failure. In that cases clearing error
> > bits is simply not possible.
> > 
> > To avoid some possible interrupt storms (the chip detect a failure, set its
> > interrupt line but could be not accessible anymore), the best thing to do
> > is to disable the interrupt line here, let the reset work to do its job
> > performing a full reset of the device and re-enabling the interrupt line
> > when needed, probably in sn65dsi83_atomic_enable().
> > 
> > What do you think about that?  
> 
> As I read the datasheet this is a active-high level interrupt, so as
> long as some enabled IRQs are pending the signal will stay high.
> There are 3 notes in section 9.1.3. IRQ usage that in various situations
> IRQ bits may be set/pending and have to be cleared.
> At least clear the interrupts before enabling it again to be on the
> safe side.

Ok, I finally disable the irq just before the schedule_work(&ctx->reset_work)
call and re-enable it after the sn65dsi83_reset_pipe(ctx) call done
in sn65dsi83_reset_work().

During sn65dsi83_reset_pipe(), sn65dsi83_atomic_disable() and
sn65dsi83_atomic_enable() are called and so interrupts are cleared.

This modification will be part of the next iteration.

Best regards,
Hervé