linux-kernel - Re: [PATCH 1/2] drm/bridge: sii902x: Enable I/O and core VCC supplies if present

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Date:   Mon, 28 Sep 2020 12:35:01 -0500
From:   "Alex G." <mr.nuke.me@...il.com>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        David Airlie <airlied@...ux.ie>,
        Mark Brown <broonie@...nel.org>,
        Jonas Karlman <jonas@...boo.se>, linux-kernel@...r.kernel.org,
        Andrzej Hajda <a.hajda@...sung.com>,
        Rob Herring <robh+dt@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH 1/2] drm/bridge: sii902x: Enable I/O and core VCC supplies
 if present

On 9/26/20 1:49 PM, Sam Ravnborg wrote:
> Hi Alexandru
> 
> On Thu, Sep 24, 2020 at 03:05:05PM -0500, Alexandru Gagniuc wrote:
>> On the SII9022, the IOVCC and CVCC12 supplies must reach the correct
>> voltage before the reset sequence is initiated. On most boards, this
>> assumption is true at boot-up, so initialization succeeds.
>>
>> However, when we try to initialize the chip with incorrect supply
>> voltages, it will not respond to I2C requests. sii902x_probe() fails
>> with -ENXIO.
>>
>> To resolve this, look for the "iovcc" and "cvcc12" regulators, and
>> make sure they are enabled before starting the reset sequence. If
>> these supplies are not available in devicetree, then they will default
>> to dummy-regulator. In that case everything will work like before.
>>
>> This was observed on a STM32MP157C-DK2 booting in u-boot falcon mode.
>> On this board, the supplies would be set by the second stage
>> bootloader, which does not run in falcon mode.
>>
>> Signed-off-by: Alexandru Gagniuc <mr.nuke.me@...il.com>
> 
> One nitpick here. The binding should be present in the tree before
> you start using it. So this patch should be applied after the binding.

It is :)
   * arch/arm/boot/dts/stm32mp15xx-dkx.dtsi

Alex

> One detail below - I think others have already commented on the rest.
[snip]