linux-kernel - Re: [PATCH] drm/bridge: adv7511: Exit interrupt handling when necessary

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Message-ID: <CAA8EJppH1rYQ5pzkGP+V-=cOPBYMWm=ZK2Ei1ttjOiN6GRDP+w@mail.gmail.com>
Date: Mon, 20 May 2024 14:13:07 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Sui Jingfeng <sui.jingfeng@...ux.dev>
Cc: Liu Ying <victor.liu@....com>, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, andrzej.hajda@...el.com, 
	neil.armstrong@...aro.org, rfoss@...nel.org, 
	Laurent.pinchart@...asonboard.com, jonas@...boo.se, jernej.skrabec@...il.com, 
	maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de, 
	airlied@...il.com, daniel@...ll.ch, biju.das.jz@...renesas.com, 
	u.kleine-koenig@...gutronix.de, aford173@...il.com, jani.nikula@...el.com, 
	bli@...g-olufsen.dk
Subject: Re: [PATCH] drm/bridge: adv7511: Exit interrupt handling when necessary

On Mon, 20 May 2024 at 14:11, Sui Jingfeng <sui.jingfeng@...ux.dev> wrote:
>
> Hi,
>
> On 5/20/24 06:11, Dmitry Baryshkov wrote:
> > On Thu, May 16, 2024 at 06:10:06PM +0800, Liu Ying wrote:
> >> Commit f3d9683346d6 ("drm/bridge: adv7511: Allow IRQ to share GPIO pins")
> >> fails to consider the case where adv7511->i2c_main->irq is zero, i.e.,
> >> no interrupt requested at all.
> >>
> >> Without interrupt, adv7511_wait_for_edid() could return -EIO sometimes,
> >> because it polls adv7511->edid_read flag by calling adv7511_irq_process()
> >> a few times, but adv7511_irq_process() happens to refuse to handle
> >> interrupt by returning -ENODATA.  Hence, EDID retrieval fails randomly.
> >>
> >> Fix the issue by checking adv7511->i2c_main->irq before exiting interrupt
> >> handling from adv7511_irq_process().
> >>
> >> Fixes: f3d9683346d6 ("drm/bridge: adv7511: Allow IRQ to share GPIO pins")
> >> Signed-off-by: Liu Ying <victor.liu@....com>
> >> ---
> >>   drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 3 ++-
> >>   1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> >> index 6089b0bb9321..2074fa3c1b7b 100644
> >> --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> >> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> >> @@ -479,7 +479,8 @@ static int adv7511_irq_process(struct adv7511 *adv7511, bool process_hpd)
> >>              return ret;
> >>
> >>      /* If there is no IRQ to handle, exit indicating no IRQ data */
> >> -    if (!(irq0 & (ADV7511_INT0_HPD | ADV7511_INT0_EDID_READY)) &&
> >> +    if (adv7511->i2c_main->irq &&
> >> +        !(irq0 & (ADV7511_INT0_HPD | ADV7511_INT0_EDID_READY)) &&
> >>          !(irq1 & ADV7511_INT1_DDC_ERROR))
> >>              return -ENODATA;
> >
> > I think it might be better to handle -ENODATA in adv7511_wait_for_edid()
> > instead. WDYT?
> >
>
> I think this is may deserve another patch.

My point is that the IRQ handler is fine to remove -ENODATA here,
there is no pending IRQ that can be handled. So instead of continuing
the execution when we know that IRQ bits are not set, it's better to
ignore -ENODATA in the calling code and go on with msleep().

-- 
With best wishes
Dmitry