linux-kernel - Re: [PATCH v3 2/3] drm/bridge: sii902x: Enable I/O and core VCC supplies if present

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Date:   Sun, 8 Nov 2020 11:55:35 +0100
From:   Sam Ravnborg <sam@...nborg.org>
To:     Alexandru Gagniuc <mr.nuke.me@...il.com>
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>,
        open list <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 v3 2/3] drm/bridge: sii902x: Enable I/O and core VCC
 supplies if present

Hi Alexandru

On Tue, Oct 20, 2020 at 05:14:58PM -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>

Thanks, applied series to drm-misc-next. I fixed two
checkpatch --strict warnings while applying.

	Sam