From: mark.yao@rock-chips•com (Mark yao)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 3/3] drm/rockchip: explain why we can't wait_for_vblanks
Date: Mon, 18 Jan 2016 09:40:32 +0800 [thread overview]
Message-ID: <569C4290.1030902@rock-chips.com> (raw)
In-Reply-To: <20160114162619.233ab39c.john@metanate.com>
On 2016?01?15? 00:26, John Keeping wrote:
> On Thu, 14 Jan 2016 15:57:05 +0100, Thierry Reding wrote:
>
>> On Thu, Jan 14, 2016 at 02:39:42PM +0000, John Keeping wrote:
>>> Signed-off-by: John Keeping <john@metanate•com>
>>> ---
>>> drivers/gpu/drm/rockchip/rockchip_drm_fb.c | 6 ++++++
>>> 1 file changed, 6 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
>>> index 679d23a..b267ce4 100644
>>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
>>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
>>> @@ -177,6 +177,12 @@ static void rockchip_crtc_wait_for_update(struct drm_crtc *crtc)
>>> crtc_funcs->wait_for_update(crtc);
>>> }
>>>
>>> +/*
>>> + * We can't use drm_atomic_helper_wait_for_vblanks() because rk3288 and rk3066
>>> + * have hardware counters for neither vblanks nor scanlines. This function is
>>> + * equivalent but uses rockchip_crtc_wait_for_update() instead of waiting for
>>> + * vblank_count to change.
>>> + */
>> This is kind of misleading. From reading earlier parts of the thread the
>> reason why drm_atomic_helper_wait_for_vblanks() won't work is because it
>> has a potential race condition that can't be detected unless you also
>> have a vblank counter. However, the above comment makes it work like
>> drm_atomic_helper_wait_for_vblanks() doesn't work in the absence of a
>> vblank counter, which isn't quite true.
> How about something like this (using the sequence from Mark's message):
>
> /*
> * We can't use drm_atomic_helper_wait_for_vblanks() because rk3288 and rk3066
> * have hardware counters for neither vblanks nor scanlines, which results in
> * a race where:
> * | <-- HW vsync irq and reg take effect
> * plane_commit --> |
> * get_vblank and wait --> |
> * | <-- handle_vblank, vblank->count + 1
> * cleanup_fb --> |
> * iommu crash --> |
> * | <-- HW vsync irq and reg take effect
> *
> * This function is equivalent but uses rockchip_crtc_wait_for_update() instead
> * of waiting for vblank_count to change.
> */
>
>
>
Looks good for me, but maybe Thierry has some more advices. :-)
--
?ark Yao
next prev parent reply other threads:[~2016-01-18 1:40 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-13 12:53 [RFC/PATCH] drm/rockchip: don't wait for vblank if fb hasn't changed John Keeping
2016-01-13 14:23 ` Daniel Vetter
2016-01-13 14:34 ` John Keeping
2016-01-13 15:40 ` Daniel Vetter
2016-01-13 15:55 ` John Keeping
2016-01-13 16:21 ` Daniel Vetter
2016-01-13 16:40 ` John Keeping
2016-01-13 17:19 ` Daniel Vetter
2016-01-13 17:39 ` John Keeping
2016-01-14 1:16 ` Mark yao
2016-01-14 8:32 ` Daniel Vetter
2016-01-14 8:46 ` Mark yao
2016-01-14 14:20 ` Daniel Vetter
2016-01-14 14:39 ` [PATCH 0/3] drm/rockchip: fix cursor performance with atomic John Keeping
2016-01-14 14:39 ` [PATCH 1/3] drm/atomic-helper: Export framebuffer_changed() John Keeping
2016-01-14 14:56 ` Daniel Vetter
2016-01-14 14:39 ` [PATCH 2/3] drm/rockchip: don't wait for vblank if fb hasn't changed John Keeping
2016-01-14 14:39 ` [PATCH 3/3] drm/rockchip: explain why we can't wait_for_vblanks John Keeping
2016-01-14 14:57 ` Thierry Reding
2016-01-14 16:26 ` John Keeping
2016-01-18 1:40 ` Mark yao [this message]
2016-01-19 10:46 ` [PATCH v2 0/3] drm/rockchip: fix cursor performance with atomic John Keeping
2016-01-19 10:46 ` [PATCH v2 1/3] drm/atomic-helper: Export framebuffer_changed() John Keeping
2016-01-19 11:03 ` Daniel Vetter
2016-01-19 10:46 ` [PATCH v2 2/3] drm/rockchip: don't wait for vblank if fb hasn't changed John Keeping
2016-01-19 10:47 ` [PATCH v2 3/3] drm/rockchip: explain why we can't wait_for_vblanks John Keeping
2016-01-21 0:51 ` [PATCH v2 0/3] drm/rockchip: fix cursor performance with atomic Mark yao
2016-01-17 15:21 ` [RFC/PATCH] drm/rockchip: don't wait for vblank if fb hasn't changed Heiko Stuebner
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