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From:   Eric Anholt <eric@anholt.net>
To:     Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Cc:     David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Eben Upton <eben@raspberrypi.org>,
        Daniel Stone <daniel@fooishbar.org>,
        Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Subject: Re: [PATCH v4 3/4] drm/vc4: Check for the binner bo before handling OOM interrupt
In-Reply-To: <20190403154856.9470-4-paul.kocialkowski@bootlin.com>
References: <20190403154856.9470-1-paul.kocialkowski@bootlin.com> <20190403154856.9470-4-paul.kocialkowski@bootlin.com>
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Date:   Wed, 03 Apr 2019 11:58:01 -0700
Message-ID: <87ef6ior0m.fsf@anholt.net>
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Paul Kocialkowski <paul.kocialkowski@bootlin.com> writes:

> Since the OOM interrupt directly deals with the binner bo, it doesn't
> make sense to try and handle it without a binner buffer registered.
> The interrupt will kick again in due time, so we can safely ignore it
> without a binner bo allocated.
>
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> ---
>  drivers/gpu/drm/vc4/vc4_irq.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_irq.c b/drivers/gpu/drm/vc4/vc4_irq.c
> index ffd0a4388752..723dc86b4511 100644
> --- a/drivers/gpu/drm/vc4/vc4_irq.c
> +++ b/drivers/gpu/drm/vc4/vc4_irq.c
> @@ -64,6 +64,9 @@ vc4_overflow_mem_work(struct work_struct *work)
>  	struct vc4_exec_info *exec;
>  	unsigned long irqflags;

Since OOM handling is tricky, could we add a comment to help the next
person try to understand it:

/* The OOM IRQ is level-triggered, so we'll see one at power-on before
 * any jobs are submitted.  The OOM IRQ is masked when this work is
 * scheduled, so we can safely return if there's no binner memory
 * (because no client is currently using 3D).  When a bin job is
 * later submitted, its tile memory allocation will end up bringing us
 * back to a non-OOM state so the OOM can be triggered again.
 */

But, actually, I don't see how the OOM IRQ will ever get re-enabled.

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