linux-kernel - Re: [PATCH 1/2] regmap: add regmap_might

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Date:   Fri, 30 Apr 2021 18:26:03 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Michael Walle <michael@...le.cc>
Cc:     linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH 1/2] regmap: add regmap_might_sleep()

On Fri, Apr 30, 2021 at 06:01:49PM +0200, Michael Walle wrote:
> Am 2021-04-30 17:19, schrieb Mark Brown:

> > Whatever is creating the regmap really ought to know what device it's
> > dealing with...

> But creating and using the regmap are two seperate things, no? Consider
> the gpio-sl28cpld. It will just use whatever regmap the parent has created.
> How would it know what type of regmap it is?

But that's a driver for a specific device AFAICT which looks like it's
only got an I2C binding on the MFD so the driver knows that it's for a
device that's on a bus that's going to sleep and doesn't need to infer
anything?  This looks like the common case I'd expect where there's no
variation.

> > > It might be possible to pass this information via the
> > > gpio_regmap_config, but this has the following drawbacks. First, that
> > > property is redundant and both places might contratict each other. And
> > > secondly, the driver might not even know the type of the regmap
> > > because
> > > it just gets an opaque pointer by querying the device tree.

> > If it's a generic GPIO driver from a code correctness point of view it's
> > always got a risk of sleeping...

> I can't follow you here.

If users happen to end up with a map flagged as fast they can work on
the whatever driver uses this stuff and not realise they're breaking
other users of the same driver that end up with slow I/O.  The whole
point of the flag in GPIO is AIUI warnings to help with that case.

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