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

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Message-ID: <2a2e9a4c-b888-45e1-a191-847dd8e7cb9d@gmail.com>
Date: Mon, 31 Mar 2025 14:34:22 +0200
From: Christian König <ckoenig.leichtzumerken@...il.com>
To: James Flowers <bold.zone2373@...tmail.com>, harry.wentland@....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

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.

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