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 09:44:17 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
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

On Tue, Nov 22, 2016 at 9:38 AM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> 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 ?

Partially, but not completely as I just explained in the other mail thread.

>> 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 ?

So I initially thought it was the HPD pulse, but I'm finding that
without the regmap_sync I still see the i2c_transfer errors.

I need to figure out how to decompose the regmap_sync to try to narrow
it down further.

thanks
-john