linux-kernel - Re: [PATCH -next] pwm: pca9685: Remove set but not used variable 'pwm'

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Message-ID: <CAGngYiVDCCjo6VKt660Uz5mbEGOBOZpcUWeRHWx_L=TapZgv_w@mail.gmail.com>
Date:   Mon, 3 Jun 2019 11:08:06 -0400
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        YueHaibing <yuehaibing@...wei.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-pwm@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] pwm: pca9685: Remove set but not used variable 'pwm'

On Mon, Jun 3, 2019 at 7:40 AM Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
>
> I think you are right. pca9685_pwm_request() should take the mutex as
> long as it is requesting PWM.

Yes, but things get hairy because pca9685_pwm_request() will have to
give up the mutex when it returns. I cannot see a way to keep holding
this mutex while the in-use flag is set by the pwm core ?

Alternatively, we could set (void *)1 pwm_data inside the pwm_request,
wrapped inside the mutex.
But then things get 'messy'.

> A flag would probably be easier to understand than the magic we have
> now.

I have the feeling that a flag (plus a mutex) would be the clearest and
safest way forward. I'll post a patch soon, you guys tell me what you
think.

Unfortunately, I no longer have any test hardware. The project that
required this chip is long dead.