linux-kernel - Re: [PATCH 2/2] drm/vc4: Ensure interrupts are disabled

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Date:   Tue, 14 Nov 2017 12:43:31 +0100
From:   Stefan Schake <stschake@...il.com>
To:     Eric Anholt <eric@...olt.net>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-rpi-kernel@...ts.infradead.org,
        David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] drm/vc4: Ensure interrupts are disabled

On Tue, Nov 14, 2017 at 1:18 AM, Eric Anholt <eric@...olt.net> wrote:
> Stefan Schake <stschake@...il.com> writes:
>
>> The overflow mem work callback vc4_overflow_mem_work reenables its
>> associated interrupt upon completion. To ensure all interrupts are disabled
>> when we return from vc4_irq_uninstall, we need to disable it again if
>> cancel_work_sync indicated pending work.
>
> Is there a reason we need the interrupts disabled at the V3D level while
> we have the IRQ disabled at the irqchip level?  Once we re-enable at the
> irqchip, we immediately V3D_WRITE(V3D_INTENA, V3D_DRIVER_IRQS) anyway.

irqchip will mask it in the ARM interrupt controller, so we will certainly never
see an interrupt. I'm not sure on the exact guarantees V3D_INTENA and
V3D_INTCTL make - does the state in INTENA affect if V3D will signal an
interrupt in INTCTL? We're not currently clearing the latter in postinstall.

>From a practical perspective, we're not doing anything in between uninstall
and postinstall that would trigger the interrupt. So in that sense
it's certainly
superfluous.