linux-kernel - Re: [PATCH] drm/amd/display: replace use of msleep(<20) with usleep

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Message-ID: <81cac86c-dece-4f0d-abd7-efd888a08db0@amd.com>
Date: Mon, 31 Mar 2025 14:20:53 -0400
From: Harry Wentland <harry.wentland@....com>
To: Christian König <ckoenig.leichtzumerken@...il.com>,
 James Flowers <bold.zone2373@...tmail.com>, sunpeng.li@....com,
 siqueira@...lia.com, alexander.deucher@....com, christian.koenig@....com,
 airlied@...il.com, simona@...ll.ch, aurabindo.pillai@....com,
 alex.hung@....com, skhan@...uxfoundation.org
Cc: amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 linux-kernel-mentees@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amd/display: replace use of msleep(<20) with
 usleep_range for better accuracy



On 2025-03-31 08:34, Christian König wrote:
> Am 26.03.25 um 08:00 schrieb James Flowers:
>> msleep < 20ms will often sleep for ~20ms (according to Documentation/timers/timers-howto.rst).
> 
> Our display team has to decide but I don't think that this patch is justified.
> 
> The time given to msleep is just the minimum time necessary for some HW action to take place. Waiting longer than that is usually not harmful except when you want to optimize total operation time.
> 

Agreed. Little timing changes often have unintended effects.
I have no desire to change working code unless it's required
to fix a real-life issue.

Harry

> Regards,
> Christian.
> 
>>
>> Signed-off-by: James Flowers <bold.zone2373@...tmail.com>
>> ---
>>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
>> index 2cd35392e2da..2d225735602b 100644
>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
>> @@ -682,7 +682,7 @@ static bool execute_synaptics_rc_command(struct drm_dp_aux *aux,
>>  		if (rc_cmd == cmd)
>>  			// active is 0
>>  			break;
>> -		msleep(10);
>> +		usleep_range(10000, 10200);
>>  	}
>>  
>>  	// read rc result
>