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

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Message-ID: <CAHp75VcUBFq4gRe_NwEfDqAkGrTLSK8ZY0B3UTuYOOxUBRQdbA@mail.gmail.com>
Date:   Tue, 12 Dec 2017 13:12:05 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] regmap: allow to disable all locking mechanisms

On Sun, Dec 10, 2017 at 5:14 PM, Bartosz Golaszewski <brgl@...ev.pl> wrote:
> 2017-12-10 14:10 GMT+01:00 Andy Shevchenko <andy.shevchenko@...il.com>:
>> On Wed, Dec 6, 2017 at 4:26 PM, Bartosz Golaszewski <brgl@...ev.pl> wrote:
>>> We have a use case in the at24 EEPROM driver (recently converted to
>>> using regmap instead of raw i2c/smbus calls) where we read from/write
>>> to the regmap in a loop, while protecting the entire loop with
>>> a mutex.
>>>
>>> Currently this implicitly makes us use two mutexes - one in the driver
>>> and one in regmap. While browsing the code for similar use cases I
>>> noticed a significant number of places where locking *seems* redundant.
>>>
>>> Allow users to completely disable any locking mechanisms in regmap
>>> config.
>>
>>> +static void regmap_lock_unlock_empty(void *__map)
>>
>> ..._none()?
>>
>
> Too late, Mark already applied it.

Ah, Mark always works at speed of light!

>> Why not to introduce positive switch, namely
>>  bool mutex_lock; // choose better name
>> and assign ..._none() by default?
>
> Because we don't want to break all the existing regmaps, if map->lock
> or map->unlock is empty, regmap core decides internally whether to use
> a mutex or a spinlock.

Good point.
So, it means the options like: nomutex (false — mutex is in use) or
nolock (true — disable locking).
>From those the latter looks better to me and IIUC you went that way.

-- 
With Best Regards,
Andy Shevchenko