linux-kernel - Re: [PATCH] irqchip/irq-mtk-sysirq: drop unnecessary spinlock

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Message-ID: <CAMpxmJVPB2+hD8mZ+Bo9=UVEist7BSJrZej5O9_9a_SmWyTanA@mail.gmail.com>
Date:   Wed, 27 May 2020 19:06:26 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Matthias Brugger <matthias.bgg@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        linux-mediatek@...ts.infradead.org,
        Fabien Parent <fparent@...libre.com>,
        Stephane Le Provost <stephane.leprovost@...iatek.com>,
        Pedro Tsai <pedro.tsai@...iatek.com>,
        Andrew Perepech <andrew.perepech@...iatek.com>
Subject: Re: [PATCH] irqchip/irq-mtk-sysirq: drop unnecessary spinlock

śr., 27 maj 2020 o 18:38 Marc Zyngier <maz@...nel.org> napisał(a):
>
> Sight... Do you realize that these two locks do not protect the same
> thing at all? One protects the interrupt data, and the other protects
> the MMIO register which is shared between multiple interrupts, and
> on which the driver performs a RMW.
>
> Thanks to the removal of this spinlock, two irq_set_type() can execute
> in parallel and silently corrupt the register. Not exactly an
> improvement.
>

Eek I missed the fact that the internal lock is tied to the chip, not
the interrupt. In that case I'll convert this spinlock to a raw one.

Bart