linux-kernel - Re: [PATCH v1 2/2] gpio: tegra: Use raw

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Date:   Wed, 4 Nov 2020 18:03:07 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Peter Geis <pgwipeout@...il.com>, linux-tegra@...r.kernel.org,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] gpio: tegra: Use raw_spinlock

04.11.2020 17:47, Andy Shevchenko пишет:
> On Wed, Nov 4, 2020 at 3:27 PM Dmitry Osipenko <digetx@...il.com> wrote:
>>
>> Use raw_spinlock in order to fix spurious messages about invalid context
>> when spinlock debugging is enabled. This happens because there is a legit
>> nested raw_spinlock->spinlock locking which debug code can't recognize and
>> handle.
> 
> This sounds like papering over a problem that exists somewhere else.
> 
> What I would rather make as a selling point is that raw spin locks are
> necessary to be in the RT kernel for IRQ chips.

This should be a well-known problem because other GPIO drivers also have
it.

For example this one:

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20201104&id=023892ec80f0efcffe22045e92bb89f3f1480f2d

Although, looking at it again, I think there is no real need to change
the dbc_lock since it doesn't relate to the IRQ. Perhaps this could be
improved in a v2.