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drm/amd/display: Fix divide by zero in calc_psr_num_static_frames

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calc_psr_num_static_frames() divides by vsync_rate_hz before checking
whether it is zero:

	frame_time_microsec = 1000000 / vsync_rate_hz;

This can trigger a divide-by-zero bug if an invalid refresh rate is
passed in.

Rewrite the calculation to directly compute the number of frames needed
for at least 30 ms using DIV_ROUND_UP(). This avoids the invalid divisor
and removes the temporary frame_time_microsec calculation.

Keep the existing fallback behavior of 2 static frames when
vsync_rate_hz is zero.

Fixes: 4cef2ac4c7 ("drm/amd/display: Introduce power module on Linux")
Reported-by: Dan Carpenter <error27@gmail.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Ray Wu <ray.wu@amd.com>
Cc: Chenyu Chen <chen-yu.chen@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Srinivasan Shanmugam 2026-04-23 18:46:13 +05:30 committed by Alex Deucher
parent 5cdc219fe8
commit 506e047aed
1 changed files with 4 additions and 10 deletions
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14
drivers/gpu/drm/amd/display/modules/power/power.c
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@ -157,20 +157,14 @@ static const unsigned int default_dc_backlight_percent = 70;
static unsigned int calc_psr_num_static_frames(unsigned int vsync_rate_hz)
{
/* Calculate number of static frames before generating interrupt to
* enter PSR.
*/
unsigned int frame_time_microsec = 1000000 / vsync_rate_hz;
// Init fail safe of 2 frames static
/* Initialize fail-safe to 2 static frames. */
unsigned int num_frames_static = 2;
/* Round up
* Calculate number of frames such that at least 30 ms of time has
* passed.
/* Calculate number of frames such that at least 30 ms has passed.
* Round up to ensure the static period is not shorter than 30 ms.
*/
if (vsync_rate_hz != 0)
num_frames_static = (30000 / frame_time_microsec) + 1;
num_frames_static = DIV_ROUND_UP(30000 * vsync_rate_hz, 1000000);
return num_frames_static;
}