linux-kernel - Re: regmap: mmio: lack of runtime

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Message-ID: <Yf7BI9Cei5H2S1ry@sirena.org.uk>
Date:   Sat, 5 Feb 2022 18:25:39 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Peng Fan <peng.fan@....com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        "S.j. Wang" <shengjiu.wang@....com>
Subject: Re: regmap: mmio: lack of runtime_pm support for debugfs

On Fri, Feb 04, 2022 at 11:53:01AM -0800, Brian Norris wrote:
> On Fri, Feb 4, 2022 at 11:41 AM Mark Brown <broonie@...nel.org> wrote:
> > On Fri, Feb 04, 2022 at 11:21:51AM -0800, Brian Norris wrote:

> > > We do actually have a cache for the case I care about, but there's
> > > also a debugfs file for bypassing that and...for some reason I'm
> > > dealing with some diagnostic scripts that purposely toggle that. I'm

> > Are you sure this extra thing that bypasses the cache isn't an out of
> > tree patch?  It really doesn't sound like a good idea to have that, and
> > if people think they need it they probably have drivers doing something
> > quite unfortunate.  Or are you just looking at the upstream debugfs with
> > some volatile registers?

> Again, I didn't claim the *use* of that bypass in the aforementioned
> diagnostic script was a good idea...but it's at least possible. I've
> already carved out more exceptions so that script doesn't do bad
> things on some systems, but maybe I'll poke the authors even more, to
> see if they have a good reason for using the bypass.

So it's fiddling about with bypass mode by hand rather than
something that specifically shows you the underlying device.
That is also a terrible idea for routine use, if it's telling you
anything different from what the cache says the driver is buggy
and if the script causes that to happen then it itself is likely
to be the bug.

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