linux-kernel - Re: [PATCH] regmap: allow to disable all locking mechanisms

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Message-ID: <CAMRc=Meyr6AuomZYZsuc4MnnoOcOGVDiQvPc+zA+tzsRsY1f3w@mail.gmail.com>
Date:   Tue, 12 Dec 2017 13:21:46 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Mark Brown <broonie@...nel.org>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] regmap: allow to disable all locking mechanisms

2017-12-12 13:18 GMT+01:00 Mark Brown <broonie@...nel.org>:
> On Tue, Dec 12, 2017 at 12:42:47PM +0100, Lars-Peter Clausen wrote:
>> On 12/06/2017 03:26 PM, Bartosz Golaszewski wrote:
>
>> > + * @disable_locking: This regmap is either protected by external means or
>> > + *                   is guaranteed not be be accessed from multiple threads.
>
>> To guarantee this you need to make sure that a regmap instance with this
>> flag set does not register a debugfs interface. debugfs file access happens
>> from a userspace process and hence could (and probably) is in a different
>> thread than the driver regmap access.
>
> That's true, and the debugfs is world readable too so we can't just say
> it's up to root to be sensible.

This lock is only taken when writing to cache_only and cache_bypass though.

This shouldn't cause serious trouble but yeah, we need to find a
better solution.

Maybe the right approach would be to provide users with locking
routines (regmap_lock()/regmap_unlock()) and then add a boolean
variable to the config (e.g. bool manual_locking) which would indicate
to regmap that it shouldn't take the lock in most cases (except for
debugfs) as this would be manually done by the regmap owner?

Or possibly a separate lock for map->cache_bypass/map->cache_only?

Thanks,
Bartosz