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

From: "H. Nikolaus Schaller" <hns@goldelico.com>
To: Mark Brown <broonie@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Paul Boddie <paul@boddie.org.uk>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Neil Armstrong <narmstrong@baylibre.com>,
	David Airlie <airlied@linux.ie>,
	dri-devel@lists.freedesktop.org, linux-mips@vger.kernel.org,
	Paul Cercueil <paul@crapouillou.net>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Sam Ravnborg <sam@ravnborg.org>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	devicetree@vger.kernel.org, Kees Cook <keescook@chromium.org>,
	Jonas Karlman <jonas@kwiboo.se>, Rob Herring <robh+dt@kernel.org>,
	Maxime Ripard <maxime@cerno.tech>,
	letux-kernel@openphoenux.org,
	Ezequiel Garcia <ezequiel@collabora.com>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Liam Girdwood <lgirdwood@gmail.com>,
	Robert Foss <robert.foss@linaro.org>,
	linux-kernel@vger.kernel.org,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Hans Verkuil <hverkuil-cisco@xs4all.nl>
Subject: Re: [PATCH v10 4/8] drm/ingenic: Add dw-hdmi driver for jz4780
Date: Wed, 1 Dec 2021 14:51:51 +0100	[thread overview]
Message-ID: <46070A95-0FA9-43F9-A9A9-52A7B58B88F5@goldelico.com> (raw)
In-Reply-To: <Yad69aTXcGixXvy3@sirena.org.uk>

Hi,

> Am 01.12.2021 um 14:39 schrieb Mark Brown <broonie@kernel.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