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

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Date:   Tue, 14 Nov 2017 11:44:41 -0800
From:   Eric Anholt <eric@...olt.net>
To:     Stefan Schake <stschake@...il.com>
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

Stefan Schake <stschake@...il.com> writes:

> 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.

INTENA/INTDIS writes update the state of the single register that
controls which bits of INTCTL get ORed together to raise the interrupt
outside the V3D block.

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