[PATCH 39/43] drm/amd/display: Use udelay to avoid context switch

[Harry Wentland]

On 2020-01-10 4:16 p.m., Harry Wentland wrote:
> On 2020-01-10 1:47 p.m., Liu, Zhan wrote:
>>
>>
>>> -----Original Message-----
>>> From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org> On Behalf Of
>>> Christian König
>>> Sent: 2020/January/10, Friday 10:02 AM
>>> To: Siqueira, Rodrigo <Rodrigo.Siqueira at amd.com>; amd-
>>> gfx at lists.freedesktop.org
>>> Cc: Li, Sun peng (Leo) <Sunpeng.Li at amd.com>; Cheng, Tony
>>> <Tony.Cheng at amd.com>; Tsai, Martin <Martin.Tsai at amd.com>; Lakha,
>>> Bhawanpreet <Bhawanpreet.Lakha at amd.com>; Wentland, Harry
>>> <Harry.Wentland at amd.com>
>>> Subject: Re: [PATCH 39/43] drm/amd/display: Use udelay to avoid context
>>> switch
>>>
>>> Am 10.01.20 um 15:46 schrieb Rodrigo Siqueira:
>>>> From: Martin Tsai <martin.tsai at amd.com>
>>>>
>>>> [why]
>>>> The rapid msleep operation causes the white line garbage when DAL
>>>> check flip pending status in SetVidPnSourceVisibility.
>>>> To execute this msleep will induce context switch, and longer delay
>>>> could cause worse garbage situation.
>>>>
>>>> [how]
>>>> To replace msleep with udelay.
>>>>
>>>> Signed-off-by: Martin Tsai <martin.tsai at amd.com>
>>>> Reviewed-by: Tony Cheng <Tony.Cheng at amd.com>
>>>> Acked-by: Harry Wentland <harry.wentland at amd.com>
>>>> Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira at amd.com>
>>>> ---
>>>>   drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c | 4 ++--
>>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c
>>>> b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c
>>>> index 89920924a154..0dc652e76848 100644
>>>> --- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c
>>>> +++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c
>>>> @@ -1642,9 +1642,9 @@ void dcn20_program_front_end_for_ctx(
>>>>   			struct hubp *hubp = pipe->plane_res.hubp;
>>>>   			int j = 0;
>>>>
>>>> -			for (j = 0; j < TIMEOUT_FOR_PIPE_ENABLE_MS
>>>> +			for (j = 0; j < TIMEOUT_FOR_PIPE_ENABLE_MS*1000
>>>>   					&& hubp->funcs-
>>>> hubp_is_flip_pending(hubp); j++)
>>>> -				msleep(1);
>>>> +				udelay(1);
>>>
>>> Why not using mdelay() here?
>>
>> As far as I know, mdelay() is only defined on Linux side.
>>
>> This piece of code is shared by both Linux and Windows, so we have to use a function that's available on both platforms.
>>
> 
> It was used here before so we definitely have it defined for Windows as
> well.
> 

Whoops, I misread that.

mdelay is indeed not defined on our other platforms but we could go
ahead and define it if needed.

Harry

> From the commit description it sounds like msleep wasn't tight enough
> and longer delays lead to issues here, at least on Windows.
> 
> Martin, Tony, do you have more details about this?
> 
> Thanks,
> Harry
> 
>> Zhan
>>
>>>
>>> Christian.
>>>
>>>>   		}
>>>>   	}
>>>>
>>>
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