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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Message-ID: <CALAqxLV2GD5FXQbqBnew6KMy0-eTXi+hRo8t=f1Sj_qiFGqCoQ@mail.gmail.com>
Date:   Mon, 28 Nov 2016 10:44:59 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Archit Taneja <architt@...eaurora.org>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        lkml <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        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 7:50 PM, Archit Taneja <architt@...eaurora.org> wrote:
> On 11/23/2016 01:16 AM, John Stultz wrote:
>> On Tue, Nov 22, 2016 at 9:38 AM, Laurent Pinchart
>> <laurent.pinchart@...asonboard.com> wrote:
>>> 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:
>>>>
>>>> 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 basically used regmap_sync_region() to bisect through the
>> registers to try to figure out which one calling sync on helps avoid
>> the issue, and I've narrowed it down to 0x43
>> (ADV7511_REG_EDID_I2C_ADDR).
>
>
> I guess if this register loses its state, then i2c errors are expected.
>
>>
>> If instead of the proposed patch here, I use the following patch
>> (copy/paste whitespace damage, apologies) seems to make things work
>> reliably:
>>
>> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>> b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>> index 8dba729..87403d7 100644
>> --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>>
>> @@ -555,14 +557,18 @@ static int adv7511_get_modes(struct adv7511
>> *adv7511,
>>                                      ADV7511_INT1_DDC_ERROR);
>>                 }
>>                 adv7511->current_edid_segment = -1;
>> +               regcache_sync_region(adv7511->regmap, 0x43, 0x43);
>
>
> So, we're losing register state when get_modes() is called, or sometime
> before it.
> Could you try to read a register with a known programmed value at the
> beginning of
> adv7511_get_modes(), and check if it has already lost the state or not?
>
> It's also possible that, in adv7511_get_modes(), when the chip is powered
> on, i.e,
> when we call:
>
>         regmap_update_bits(adv7511->regmap, ADV7511_REG_POWER,
>                                    ADV7511_POWER_POWER_DOWN, 0);
>
> the monitor wakes up, but there is some additional hpd toggling, which
> results
> in registers to lose their state.
>
> The patch below is something that was originally there in Lars's initial
> patch
> for ADV7533 support. I'd dropped it since it didn't have much to do with
> ADV7533
> itself. It should at least discard any HPD toggling caused by powering on
> the
> chip in the next line.
>
>
> diff --git a/drivers/gpu/drm/i2c/adv7511.c b/drivers/gpu/drm/i2c/adv7511.c
> index ed6d25d..5ee40a4 100644
> --- a/drivers/gpu/drm/i2c/adv7511.c
> +++ b/drivers/gpu/drm/i2c/adv7511.c
> @@ -654,6 +654,9 @@ static int adv7511_get_modes(struct adv7511 *adv7511,
>
>         /* Reading the EDID only works if the device is powered */
>         if (!adv7511->powered) {
> +               regmap_update_bits(adv7511->regmap, ADV7511_REG_POWER2,
> +                                  ADV7511_REG_POWER2_HPD_SRC_MASK,
> +                                  ADV7511_REG_POWER2_HPD_SRC_NONE);
>                 regmap_update_bits(adv7511->regmap, ADV7511_REG_POWER,
>                                    ADV7511_POWER_POWER_DOWN, 0);
>                 if (adv7511->i2c_main->irq) {


So this patch is what got me started on the re-using the
adv7511_power_on() logic, since it already had the bit to pulse the
HPD signal. It might be helpful, but seems like a separate issue from
the register state being lost. Unless I'm just not getting at
something more subtle that you're suggesting.

thanks
-john