linux-kernel - Re: [PATCH] drm/rockchip: Return -EBUSY if there's already a pending flip event v2

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Message-ID: <56FE5FD2.2050106@collabora.com>
Date:	Fri, 1 Apr 2016 13:47:30 +0200
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Mark yao <mark.yao@...k-chips.com>, linux-kernel@...r.kernel.org
Cc:	David Airlie <airlied@...ux.ie>, Heiko Stuebner <heiko@...ech.de>,
	dri-devel@...ts.freedesktop.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH] drm/rockchip: Return -EBUSY if there's already a pending
 flip event v2

On 04/01/2016 01:26 PM, Mark yao wrote:
> On 2016年03月31日 16:08, Tomeu Vizoso wrote:
>> As per the docs, atomic_commit should return -EBUSY "if an asycnhronous
>> updated is requested and there is an earlier updated pending".
>>
>> v2: Use the status of the workqueue instead of vop->event, and don't add
>> a superfluous wait on the workqueue.
>>
>> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
>> ---
>>  drivers/gpu/drm/rockchip/rockchip_drm_fb.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
>> index 3b8f652698f8..285f8cd5afe1 100644
>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
>> @@ -282,6 +282,9 @@ int rockchip_drm_atomic_commit(struct drm_device *dev,
>>  	struct rockchip_atomic_commit *commit = &private->commit;
>>  	int ret;
>>  
>> +	if (async && work_busy(&commit->work))
>> +		return -EBUSY;
>> +
> 
> Sorry for reply late.
> 
> There is a comment on work_busy function describe :
> 
>     "the test result is  unreliable and only useful as advisory hints or
> for debugging."
> 
> I don't know if it's suitable to use it here, does some guys know it?

I'm not sure, but if the reason is the caveat explained in
find_worker_executing_work(), then it's probably safe (and would explain
how the function is used in other parts in the kernel).

> And then, the "flush_work(&commit->work);" is no needed if return -EBUSY
> here.
> you can remove it at this patch.

We still need to wait if it's being called in sync mode.

Regards,

Tomeu

>>  	ret = drm_atomic_helper_prepare_planes(dev, state);
>>  	if (ret)
>>  		return ret;
> 
> 
> 
> -- 
> Ｍark Yao
>