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

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Message-ID: <15398572.tv2OnDr8pf@steina-w>
Date: Thu, 09 Jan 2025 11:49:13 +0100
From: Alexander Stein <alexander.stein@...tq-group.com>
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>, 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

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.

Best regards,
Alexander
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