linux-kernel - Re: [PATCH] Input: goodix-berlin - Add sysfs interface for reading and writing touch IC registers

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Message-ID: <Zjo8eTQQS1LvzFgZ@finisterre.sirena.org.uk>
Date: Tue, 7 May 2024 23:36:41 +0900
From: Mark Brown <broonie@...nel.org>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Hans de Goede <hdegoede@...hat.com>,
	Charles Wang <charles.goodix@...il.com>, hadess@...ess.net,
	Richard Hughes <hughsient@...il.com>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, neil.armstrong@...aro.org
Subject: Re: [PATCH] Input: goodix-berlin - Add sysfs interface for reading
 and writing touch IC registers

On Mon, May 06, 2024 at 07:13:38PM -0700, Dmitry Torokhov wrote:
> On Mon, May 06, 2024 at 02:03:13PM +0200, Hans de Goede wrote:

> > If raw register access is seen as a good solution, then I think this
> > should use regmap + some generic helpers (to be written) to export
> > regmap r/w access to userspace.

> I think the less code we have in kernel the better, especially if in
> cases where firmware flashing is not essential for device to work (i.e.
> it the controller has a flash memory). That said IIRC Mark felt very
> strongly about allowing regmap writes from userspace... but maybe he
> softened the stance or we could have this functionality opt-in?

I think unmediated raw register access is a terrible idea, you can't
safely write a driver if userspace can just go in and randomly write to
registers with no coordination with the running driver and for some
devices the kernel needs to ensure that any writes don't damage or
destabalise the system.  If a driver provides an interface that looks
like raw register accesses that's of course fine (I mean, a lot of
firmware formats basically boil down to register write sequences which
is clearly fine) but it should be the driver doing that and it should be
looking at what's going on and ensure that it's joined up with the needs
of the rest of the system.

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