linux-kernel - Re: [PATCH v10 4/8] drm/ingenic: Add dw-hdmi driver for jz4780

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Date:   Wed, 1 Dec 2021 14:51:51 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Paul Cercueil <paul@...pouillou.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Kees Cook <keescook@...omium.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Harry Wentland <harry.wentland@....com>,
        Sam Ravnborg <sam@...nborg.org>,
        Maxime Ripard <maxime@...no.tech>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Liam Girdwood <lgirdwood@...il.com>,
        Paul Boddie <paul@...die.org.uk>, devicetree@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        letux-kernel@...nphoenux.org, Jonas Karlman <jonas@...boo.se>,
        dri-devel@...ts.freedesktop.org,
        Ezequiel Garcia <ezequiel@...labora.com>
Subject: Re: [PATCH v10 4/8] drm/ingenic: Add dw-hdmi driver for jz4780

Hi,

> Am 01.12.2021 um 14:39 schrieb Mark Brown <broonie@...nel.org>:
> 
> On Wed, Dec 01, 2021 at 01:02:45PM +0000, Paul Cercueil wrote:
>> Le mar., nov. 30 2021 at 22:26:37 +0100, H. Nikolaus Schaller
> 
>>> +	regulator = devm_regulator_get_optional(&pdev->dev, "hdmi-5v");
>>> +	if (IS_ERR(regulator)) {
>>> +		ret = PTR_ERR(regulator);
> 
> Why is this using _optional()?  This should only be done when the supply
> can be physically absent

There can be +5V for HDMI but without a regulator that is visible to or controllable
by the driver.

So hdmi-5v can be simply missing in DTS in which case the driver does not need to
care about. The driver just can't turn it on or off.

> (in which case I'd expect to see special
> handling).

The special case is to not enable/disable the regulator if it does not exist
and assume that there is hardware providing it otherwise (the driver can't know
that except by using get_optional). This is done by the code below

>>> +	if (IS_ERR(regulator)) {

...

> +	if (!regulator)
> +		return 0;
> 
> +	ret = regulator_enable(regulator);

...

BR and thanks,
Nikolaus