linux-kernel - Re: [RFC][PATCH 1/3] drm/bridge: adv7511: Rework adv7511_power_on/off() so they can be reused internally

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Date:   Tue, 22 Nov 2016 19:38:37 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Archit Taneja <architt@...eaurora.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [RFC][PATCH 1/3] drm/bridge: adv7511: Rework adv7511_power_on/off() so they can be reused internally

Hi John,

On Tuesday 22 Nov 2016 09:25:22 John Stultz wrote:
> On Tue, Nov 22, 2016 at 12:14 AM, Laurent Pinchart wrote:
> > On Monday 21 Nov 2016 16:37:30 John Stultz wrote:
>  @@ -545,24 +554,13 @@ static int adv7511_get_modes(struct adv7511 *adv7511,
> >>       unsigned int count;
> >>       
> >>       /* Reading the EDID only works if the device is powered */
> >> 
> >> -     if (!adv7511->powered) {
> >> -             regmap_update_bits(adv7511->regmap, ADV7511_REG_POWER,
> >> -                                ADV7511_POWER_POWER_DOWN, 0);
> >> -             if (adv7511->i2c_main->irq) {
> >> -                     regmap_write(adv7511->regmap,
> >> ADV7511_REG_INT_ENABLE(0),
> >> -                                  ADV7511_INT0_EDID_READY);
> >> -                     regmap_write(adv7511->regmap,
> >> ADV7511_REG_INT_ENABLE(1),
> >> -                                  ADV7511_INT1_DDC_ERROR);
> >> -             }
> >> -             adv7511->current_edid_segment = -1;
> >> -     }
> >> +     if (!adv7511->powered)
> >> +             __adv7511_power_on(adv7511);
> > 
> > The __adv7511_power_on() function does more than the above, in particular
> > it performs an expensive regcache_sync() and calls adv7533_dsi_power_on()
> > for the ADV7533. Don't those operations have side effects that are either
> > not wanted or not needed here ? In any case this patch modifies the
> > behaviour of the driver, which needs to be documented in the kernel
> > message.
> 
> So yes, while the adv7533 bits aren't needed in the internal function,
> I'm finding the logic to pulse the HPD and the regcache_sync call seem
> to be needed side effects, as without that logic, I get i2c_transfer()
> errors in adv7511_get_edid_block().

Does this patch fix the problem without requiring the 200ms delay ?

> I'll try to rework this patch to split the two changes of reworking
> the power_on/off function to be re-used (with no logic chage), and the
> patch to reuse it in get_modes() which resolves a bug.

Have you identified which register write fixes your problem here ?

> Thanks so much for the review!

-- 
Regards,

Laurent Pinchart