linux-kernel - Re: [RFC PATCH v2 9/9] drm: mali-dp: Add writeback out-fence support

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Message-ID: <20161027101847.GC18708@e106950-lin.cambridge.arm.com>
Date:   Thu, 27 Oct 2016 11:18:47 +0100
From:   Brian Starkey <brian.starkey@....com>
To:     Gustavo Padovan <gustavo@...ovan.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org
Subject: Re: [RFC PATCH v2 9/9] drm: mali-dp: Add writeback out-fence support

On Wed, Oct 26, 2016 at 07:43:57PM -0200, Gustavo Padovan wrote:
>2016-10-26 Brian Starkey <brian.starkey@....com>:
>
>> If userspace has asked for an out-fence for the writeback, we add a
>> fence to malidp_mw_job, to be signaled when the writeback job has
>> completed.
>>
>> Signed-off-by: Brian Starkey <brian.starkey@....com>
>> ---
>>  drivers/gpu/drm/arm/malidp_hw.c |    5 ++++-
>>  drivers/gpu/drm/arm/malidp_mw.c |   18 +++++++++++++++++-
>>  drivers/gpu/drm/arm/malidp_mw.h |    3 +++
>>  3 files changed, 24 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/arm/malidp_hw.c b/drivers/gpu/drm/arm/malidp_hw.c
>> index 1689547..3032226 100644
>> --- a/drivers/gpu/drm/arm/malidp_hw.c
>> +++ b/drivers/gpu/drm/arm/malidp_hw.c
>> @@ -707,8 +707,11 @@ static irqreturn_t malidp_se_irq(int irq, void *arg)
>>  		unsigned long irqflags;
>>  		/*
>>  		 * We can't unreference the framebuffer here, so we queue it
>> -		 * up on our threaded handler.
>> +		 * up on our threaded handler. However, signal the fence
>> +		 * as soon as possible
>>  		 */
>> +		malidp_mw_job_signal(drm, malidp->current_mw, 0);
>
>Drivers should not deal with fences directly. We need some sort of
>drm_writeback_finished() that will do the signalling for you.
>

With a signature like this?
	drm_writeback_finished(struct drm_connector_state *state);

I'll have to think about how to achieve that. The state isn't
refcounted and the driver isn't in charge of it's lifetime. I'm not
sure how/where to ensure the state doesn't get destroyed before its
been signaled.

-Brian

>Gustavo
>