Date: Mon, 20 May 2024 07:46:05 -0500
From: Adam Ford <aford173@...il.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Sui Jingfeng <sui.jingfeng@...ux.dev>, 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, jani.nikula@...el.com, bli@...g-olufsen.dk
Subject: Re: [PATCH] drm/bridge: adv7511: Exit interrupt handling when necessary

On Mon, May 20, 2024 at 7:00 AM Dmitry Baryshkov
<dmitry.baryshkov@...aro.org> wrote:
>
> On Mon, 20 May 2024 at 14:48, Sui Jingfeng <sui.jingfeng@...ux.dev> wrote:
> >
> > Hi,
> >
> >
> > On 5/20/24 19:13, Dmitry Baryshkov wrote:
> > > 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, ie.,
> > >>>> 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.

Sorry about that.  I did some testing and didn't see any regressions,
but if it was random, it's likely I just was lucky to not see it.

> > >>>>
> > >>>> 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.
> >
> > But there may has other things need to do in the adv7511_irq_process()
> > function.
>
> But the function returns anyway. So, we know that the condition is broken.

When I originally submitted the patch, I only added the shared IRQ
flag without any IRQ condition checks, IRQ because I didn't want to
break anything. The feedback I got was to check to see if the IRQ was
intended by the device.  My focus was the adv7511_drv.c file because
that appears to be what the registered IRQ hander was, but after
looking through adv7511_cec, I see that adv7511_cec_irq_process checks
adv_cec_tx_raw_status and returns if there is nothing to do.

Would it make sense to move the if statement  did the following things:

-  Make adv7511_cec_irq_process return an int and modify it to return
0 in normal operation or return -ENODATA where there is nothing to do.
It already has the checks in place to determine if there is work to
do, so the impact here should be minimal.

- Move the check I added on whether or not there is an interrupt  to
the very end of adv7511_irq_process just before the return 0.

- Instead of blindly returning 0, modify the if statement to read the
state of the return code of adv7511_cec_irq_process and the IRQ flags
it already checks.  If ADV7511_INT0_HPD, ADV7511_INT0_EDID_READY and
ADV7511_INT1_DDC_ERROR are all not true and adv7511_cec_irq_process
returned early, return ENODATA, but if any of the interrupts was
present and adv7511_cec_irq_process did work, it would return 0.

I think that would cover the situation where adv7511_cec_irq_process
would get called, and also prevent a false return of the IRQ being
handled when this part didn't handle anything.

It would look something like:

cec_irq = adv7511_cec_irq_process(adv7511, irq1);

/* If there is no IRQ to handle, exit indicating no IRQ data */)
if (!(irq0 & (ADV7511_INT0_HPD | ADV7511_INT0_EDID_READY)) &&
   !(irq1 & ADV7511_INT1_DDC_ERROR) &&
  cec_irq ==  -ENODATA)
        return -ENODATA;
else
        return 0


OR...


Another alternative to all this is to modify the check that I added to
verify all the following flags which are currently checked in
adv7511_cec_irq_process :

ADV7511_INT1_CEC_TX_READY
ADV7511_INT1_CEC_TX_ARBIT_LOST
ADV7511_INT1_CEC_TX_RETRY_TIMEOUT
ADV7511_INT1_CEC_RX_READY1
ADV7511_INT1_CEC_RX_READY2
ADV7511_INT1_CEC_RX_READY3

It would look something like:

/* If there is no IRQ to handle, exit indicating no IRQ data */
if (!(irq0 & (ADV7511_INT0_HPD | ADV7511_INT0_EDID_READY)) &&
   !(irq1 & ADV7511_INT1_DDC_ERROR) &&
   !(irq1 & ADV7511_INT1_CEC_TX_READY) &&
  !(irq1 & ADV7511_INT1_CEC_TX_ARBIT_LOST) &&
  !(irq1 & ADV7511_INT1_CEC_TX_RETRY_TIMEOUT) &&
  !(irq1 & ADV7511_INT1_CEC_RX_READY1) &&
  !(irq1 & ADV7511_INT1_CEC_RX_READY2) &&
  !(irq1 & ADV7511_INT1_CEC_RX_READY3))
return -ENODATA;


Please let me know what is preferred or if there is a third possible solution.

I can write up a patch with a fixes tag later today when I get back to
my build machine.

adam
>
> >
> > > So instead of continuing
> > > the execution when we know that IRQ bits are not set,
> >
> > Even when IRQ bits are not set, it just means that there is no HPD
> > and no EDID ready-to-read signal. HDMI CEC interrupts still need
> > to process.
>
> Yes. Let's get the CEC fixed. Then maybe we won't need this commit at all.
>
> >
> >
> > > it's better to
> > > ignore -ENODATA in the calling code and go on with msleep().
> > >
> >
> > So, It's confusing to ignore the -ENODATA here.
>
> [BTW: you had quotation levels wrong in two places, I've fixed them]
>
> --
> With best wishes
> Dmitry

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