For later VBIOS versions, the fractional feedback divider is
calculated as the remainder of dividing the feedback divider by
a factor, which is set to 1000000. For reference, see:
- calculate_fb_and_fractional_fb_divider
- calc_pll_max_vco_construct
However, in case of old VBIOS versions that have
set_pixel_clock_v3, they only have 1 byte available for the
fractional feedback divider, and it's expected to be set to the
remainder from dividing the feedback divider by 10.
For reference see the legacy display code:
- amdgpu_pll_compute
- amdgpu_atombios_crtc_program_pll
This commit fixes set_pixel_clock_v3 by dividing the fractional
feedback divider passed to the function by 100000.
Fixes: 4562236b3bc0 ("drm/amd/dc: Add dc display driver (v2)")
Signed-off-by: Timur Kristóf <timur.kris...@gmail.com>
---
drivers/gpu/drm/amd/display/dc/bios/command_table.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/amd/display/dc/bios/command_table.c
b/drivers/gpu/drm/amd/display/dc/bios/command_table.c
index 2bcae0643e61..58e88778da7f 100644
--- a/drivers/gpu/drm/amd/display/dc/bios/command_table.c
+++ b/drivers/gpu/drm/amd/display/dc/bios/command_table.c
@@ -993,7 +993,7 @@ static enum bp_result set_pixel_clock_v3(
allocation.sPCLKInput.usFbDiv =
cpu_to_le16((uint16_t)bp_params->feedback_divider);
allocation.sPCLKInput.ucFracFbDiv =
- (uint8_t)bp_params->fractional_feedback_divider;
+ (uint8_t)(bp_params->fractional_feedback_divider /
100000);
allocation.sPCLKInput.ucPostDiv =
(uint8_t)bp_params->pixel_clock_post_divider;
--
2.50.1
