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drm/amd/display: Fix fractional fb divider in set_pixel_clock_v3

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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: 4562236b3b ("drm/amd/dc: Add dc display driver (v2)")
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Rodrigo Siqueira <siqueira@igalia.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 027e7acc7e)
Cc: stable@vger.kernel.org
This commit is contained in:
Timur Kristóf 2025-07-31 11:43:52 +02:00 committed by Alex Deucher
parent f14ee2e7a8
commit 1050747846
1 changed files with 1 additions and 1 deletions
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2
drivers/gpu/drm/amd/display/dc/bios/command_table.c
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@ -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;