From: Timur Kristóf Date: Thu, 31 Jul 2025 09:43:52 +0000 (+0200) Subject: drm/amd/display: Fix fractional fb divider in set_pixel_clock_v3 X-Git-Tag: v5.10.241~129 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=66ba142a792b4f6d3079fb24d610143748ee0cd8;p=thirdparty%2Fkernel%2Fstable.git drm/amd/display: Fix fractional fb divider in set_pixel_clock_v3 commit 10507478468f165ea681605d133991ed05cdff62 upstream. 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 Acked-by: Alex Deucher Reviewed-by: Rodrigo Siqueira Reviewed-by: Alex Hung Signed-off-by: Alex Deucher (cherry picked from commit 027e7acc7e17802ebf28e1edb88a404836ad50d6) Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman --- 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 afc10b954ffa7..c45fe45ae564b 100644 --- a/drivers/gpu/drm/amd/display/dc/bios/command_table.c +++ b/drivers/gpu/drm/amd/display/dc/bios/command_table.c @@ -992,7 +992,7 @@ 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;