Re: [PATCH] drm/amd/display: fix 64 bit divide in freesync code

From: Nathan Chancellor <nathan@kernel.org>
To: Alex Deucher <alexander.deucher@amd.com>
Cc: Aric Cyr <Aric.Cyr@amd.com>, Anthony Koo <Anthony.Koo@amd.com>,
	kernel test robot <lkp@intel.com>,
	amd-gfx@lists.freedesktop.org, Angus Wang <Angus.Wang@amd.com>
Subject: Re: [PATCH] drm/amd/display: fix 64 bit divide in freesync code
Date: Thu, 7 Apr 2022 16:31:43 -0700	[thread overview]
Message-ID: <Yk90X7v8hIgmX5Q5@dev-arch.thelio-3990X> (raw)
In-Reply-To: <20220407195029.1581581-1-alexander.deucher@amd.com>

On Thu, Apr 07, 2022 at 03:50:29PM -0400, Alex Deucher wrote:
> Use do_div() rather than a a 64 bit divide.
> 
> Fixes: 3fe5739db48843 ("drm/amd/display: Add flip interval workaround")
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
> Cc: Angus Wang <Angus.Wang@amd.com>
> Cc: Anthony Koo <Anthony.Koo@amd.com>
> Cc: Aric Cyr <Aric.Cyr@amd.com>
> ---
>  drivers/gpu/drm/amd/display/modules/freesync/freesync.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
> index 0130f1879116..70f06fa8cc2b 100644
> --- a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
> +++ b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
> @@ -1230,6 +1230,7 @@ void mod_freesync_handle_v_update(struct mod_freesync *mod_freesync,
>  {
>  	struct core_freesync *core_freesync = NULL;
>  	unsigned int cur_timestamp_in_us;
> +	unsigned long long tmp;
>  
>  	if ((mod_freesync == NULL) || (stream == NULL) || (in_out_vrr == NULL))
>  		return;
> @@ -1239,7 +1240,9 @@ void mod_freesync_handle_v_update(struct mod_freesync *mod_freesync,
>  	if (in_out_vrr->supported == false)
>  		return;
>  
> -	cur_timestamp_in_us = dm_get_timestamp(core_freesync->dc->ctx)/10;
> +	tmp = dm_get_timestamp(core_freesync->dc->ctx);
> +	do_div(tmp, 10);
> +	cur_timestamp_in_us = tmp;

Any reason not to use

cur_timestamp_in_us = div_u64(dm_get_timestamp(core_freesync->dc->ctx), 10)

and save a variable?

>  	in_out_vrr->flip_interval.vsyncs_between_flip++;
>  	in_out_vrr->flip_interval.v_update_timestamp_in_us = cur_timestamp_in_us;
> -- 
> 2.35.1
> 
> 