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

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Message-Id: <EDWF3R.CMVWMJL42OH9@crapouillou.net>
Date:   Wed, 01 Dec 2021 14:03:14 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Mark Brown <broonie@...nel.org>, 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 Nikolaus, Mark,

Le mer., déc. 1 2021 at 14:51:51 +0100, H. Nikolaus Schaller 
<hns@...delico.com> a écrit :
> 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.

There is always a power supply though. Either a controllable one 
(through e.g. a GPIO), or it's just connected to the mains +5V; the pin 
is never left floating. In the second case, in DTS the "hdmi-5v" would 
be connected to some 5v regulator, even if it's just a dummy VCC-5V 
regulator. So Mark has a point.

> 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.

Please make it mandatory in DTS then, and use devm_regulator_get() in 
the driver.

Cheers,
-Paul

>>  (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
> 
> 
> 
>