[PATCH] drm/amd/display: prevent potential division by zero errors

[PATCH] drm/amd/display: prevent potential division by zero errors

[Hamza Mahfooz]

There are two places in apply_below_the_range() where it's possible for
a divide by zero error to occur. So, to fix this make sure the divisor
is non-zero before attempting the computation in both cases.

Cc: stable@vger.kernel.org
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2637
Fixes: a463b263032f ("drm/amd/display: Fix frames_to_insert math")
Fixes: ded6119e825a ("drm/amd/display: Reinstate LFC optimization")
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
---
 drivers/gpu/drm/amd/display/modules/freesync/freesync.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
index dbd60811f95d..ef3a67409021 100644
--- a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
+++ b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
@@ -338,7 +338,9 @@ static void apply_below_the_range(struct core_freesync *core_freesync,
 		 *  - Delta for CEIL: delta_from_mid_point_in_us_1
 		 *  - Delta for FLOOR: delta_from_mid_point_in_us_2
 		 */
-		if ((last_render_time_in_us / mid_point_frames_ceil) < in_out_vrr->min_duration_in_us) {
+		if (mid_point_frames_ceil &&
+		    (last_render_time_in_us / mid_point_frames_ceil) <
+		    in_out_vrr->min_duration_in_us) {
 			/* Check for out of range.
 			 * If using CEIL produces a value that is out of range,
 			 * then we are forced to use FLOOR.
@@ -385,8 +387,9 @@ static void apply_below_the_range(struct core_freesync *core_freesync,
 		/* Either we've calculated the number of frames to insert,
 		 * or we need to insert min duration frames
 		 */
-		if (last_render_time_in_us / frames_to_insert <
-				in_out_vrr->min_duration_in_us){
+		if (frames_to_insert &&
+		    (last_render_time_in_us / frames_to_insert) <
+		    in_out_vrr->min_duration_in_us){
 			frames_to_insert -= (frames_to_insert > 1) ?
 					1 : 0;
 		}
-- 
2.41.0

Re: [PATCH] drm/amd/display: prevent potential division by zero errors

[Aurabindo Pillai]

On 2023-09-05 14:53, Hamza Mahfooz wrote:
> There are two places in apply_below_the_range() where it's possible for
> a divide by zero error to occur. So, to fix this make sure the divisor
> is non-zero before attempting the computation in both cases.
> 
> Cc: stable@vger.kernel.org
> Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2637
> Fixes: a463b263032f ("drm/amd/display: Fix frames_to_insert math")
> Fixes: ded6119e825a ("drm/amd/display: Reinstate LFC optimization")
> Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
> ---
>   drivers/gpu/drm/amd/display/modules/freesync/freesync.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
> index dbd60811f95d..ef3a67409021 100644
> --- a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
> +++ b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
> @@ -338,7 +338,9 @@ static void apply_below_the_range(struct core_freesync *core_freesync,
>   		 *  - Delta for CEIL: delta_from_mid_point_in_us_1
>   		 *  - Delta for FLOOR: delta_from_mid_point_in_us_2
>   		 */
> -		if ((last_render_time_in_us / mid_point_frames_ceil) < in_out_vrr->min_duration_in_us) {
> +		if (mid_point_frames_ceil &&
> +		    (last_render_time_in_us / mid_point_frames_ceil) <
> +		    in_out_vrr->min_duration_in_us) {
>   			/* Check for out of range.
>   			 * If using CEIL produces a value that is out of range,
>   			 * then we are forced to use FLOOR.
> @@ -385,8 +387,9 @@ static void apply_below_the_range(struct core_freesync *core_freesync,
>   		/* Either we've calculated the number of frames to insert,
>   		 * or we need to insert min duration frames
>   		 */
> -		if (last_render_time_in_us / frames_to_insert <
> -				in_out_vrr->min_duration_in_us){
> +		if (frames_to_insert &&
> +		    (last_render_time_in_us / frames_to_insert) <
> +		    in_out_vrr->min_duration_in_us){
>   			frames_to_insert -= (frames_to_insert > 1) ?
>   					1 : 0;
>   		}


Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>

--

Thanks & Regards,
Jay