linux-kernel - Re: [PATCH v8 4/8] drm/ingenic: Add dw-hdmi driver for jz4780

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Date:   Wed, 24 Nov 2021 22:28:43 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     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>,
        Ezequiel Garcia <ezequiel@...labora.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>,
        Mark Brown <broonie@...nel.org>,
        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
Subject: Re: [PATCH v8 4/8] drm/ingenic: Add dw-hdmi driver for jz4780

Hi Paul,


>>> You probably should disable the regulator (if not NULL) here.
>> Indeed. Would it be ok to make struct regulator *regulator static
>> or do we need dynamically allocated memory?
> 
> static non-const is almost always a bad idea, so avoid it.

Well some years ago it was a perfectly simple solution that still works...
But I asked because I had a lot of doubt.

> 
> You can either:
> 
> - create a "ingenic_dw_hdmi" struct that will contain a pointer to dw_hdmi and a pointer to the regulator. Instanciate it in the probe with devm_kzalloc() and set the pointers, then set it as the driver data (platform_set_drvdata). In the remove function you can then obtain the pointer to your ingenic_dw_hdmi struct with platform_get_drvdata(), and you can remove the dw_hdmi and unregister the regulator.
> 
> - register cleanup functions, using devm_add_action_or_reset(dev, f, priv). When it's time to cleanup, the kernel core will call f(priv) automatically. So you can add a small wrapper around dw_hdmi_remove() and another one around regulator_disable(), and those will be called automatically if your probe function fails, or when the driver is removed. Then you can completely remove the ".remove" callback. There are a few examples of these in the ingenic-drm-drv.c if you want to take a look.

The second one turned out to be cleaner to handle special cases like if there is no regulator. We just register the disabler only if there is a regulator and enable succeeds.

So v9 is coming now.

BR and thanks,
Nikolaus