linux-kernel - Re: [PATCH 4/4] hwmon: (oxp-sensors) Cache state of PWM enable mode

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Message-ID: <5eef3ba8-3e6b-4672-94fd-a98920f79e4e@roeck-us.net>
Date: Tue, 7 Jan 2025 09:43:31 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>
Cc: Derek John Clark <derekjohn.clark@...il.com>,
	Joaquín Ignacio Aramendía <samsagax@...il.com>,
	Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] hwmon: (oxp-sensors) Cache state of PWM enable mode

On Fri, Dec 27, 2024 at 12:13:40AM +0100, Tobias Jakobi wrote:
> On 12/26/24 22:05, Guenter Roeck wrote:
> > On Thu, Dec 26, 2024 at 06:00:19PM +0100, tjakobi@...h.uni-bielefeld.de wrote:
> > > From: Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>
> > > 
> > > The driver is in full control of the enable mode, so we
> > > don't need to read it from HW every single time.
> > > 
> > 
> > That is not a reason for adding that much additional code.
> > What is the problem that is being solved, and why is it worth that much
> > additional code ?
> I don't think it's that much additional code, but anyway: Reading from EC is
> not exactly fast, and I want this value cached for another reason. It turns
> out that some devices use a different scaling for the PWM value depending on
> whether the PWM is controlled automatically by the EC, or manually through
> the driver. And I don't want to do an additional EC read to figure this out,
> if I can avoid it.

Maybe it isn't that much code after the runtime feature checks are removed.
Either case, since there are now two operations (reading/writing from/to
the EC and caching the result), all associated operations will need to be
mutex protected.

Guenter