linux-kernel - Re: [PATCH v5 1/2] gpio: add GPO driver for PCA9570

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Date:   Tue, 7 Jul 2020 18:07:26 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Sungbo Eo <mans0n@...ani.run>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Michael Walle <michael@...le.cc>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-gpio <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v5 1/2] gpio: add GPO driver for PCA9570

On Tue, Jul 7, 2020 at 5:03 PM Sungbo Eo <mans0n@...ani.run> wrote:
> On 20. 7. 6. 오후 9:00, Andy Shevchenko wrote:

...

> But I don't really understand what mutex does here. The driver does not
> need consecutive commands, it only sends/receives only one byte at a
> time. And AFAIK each i2c_smbus function is already protected by a mutex.
> So what should be exactly inside the lock? Should we protect the output
> buffer as well? I'm not an expert on this so please enlighten me.

There are questions, answering them will give you a solution:
- Since we have two functions doing i2c communications, can they
clash? If so, does the i2c framework guarantee the serialisation?
- Since we have a shared resource (buf), can accessors clash? How do
we guarantee serialization?

-- 
With Best Regards,
Andy Shevchenko