From: "Timur Kristóf" <timur.kristof@gmail.com>
To: amd-gfx@lists.freedesktop.org
Cc: "Timur Kristóf" <timur.kristof@gmail.com>
Subject: [PATCH 7/7] drm/amd/display: Fix fractional fb divider in set_pixel_clock_v3
Date: Thu, 31 Jul 2025 11:43:52 +0200 [thread overview]
Message-ID: <20250731094352.29528-8-timur.kristof@gmail.com> (raw)
In-Reply-To: <20250731094352.29528-1-timur.kristof@gmail.com>
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.kristof@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
next prev parent reply other threads:[~2025-07-31 9:44 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-31 9:43 [PATCH 0/7] DC: don't overclock DCE 6-10 and other fixes Timur Kristóf
2025-07-31 9:43 ` [PATCH 1/7] drm/amd/display: Don't overclock DCE 6 by 15% Timur Kristóf
2025-08-04 15:54 ` Alex Deucher
2025-08-12 22:11 ` Rodrigo Siqueira
2025-07-31 9:43 ` [PATCH 2/7] drm/amd/display: Adjust DCE 8-10 clock, don't overclock " Timur Kristóf
2025-08-04 15:56 ` Alex Deucher
2025-08-04 16:35 ` Timur Kristóf
2025-08-04 16:57 ` Alex Deucher
2025-08-12 22:18 ` Rodrigo Siqueira
2025-07-31 9:43 ` [PATCH 3/7] drm/amd/display: Find first CRTC and its line time in dce110_fill_display_configs Timur Kristóf
2025-08-04 15:57 ` Alex Deucher
2025-08-12 22:32 ` Rodrigo Siqueira
2025-07-31 9:43 ` [PATCH 4/7] drm/amd/display: Fill display clock and vblank " Timur Kristóf
2025-08-04 15:58 ` Alex Deucher
2025-08-12 22:39 ` Rodrigo Siqueira
2025-07-31 9:43 ` [PATCH 5/7] drm/amd/display: Don't warn when missing DCE encoder caps Timur Kristóf
2025-08-04 15:59 ` Alex Deucher
2025-08-12 22:47 ` Rodrigo Siqueira
2025-07-31 9:43 ` [PATCH 6/7] drm/amd/display: Don't print errors for nonexistent connectors Timur Kristóf
2025-08-04 15:59 ` Alex Deucher
2025-08-12 22:59 ` Rodrigo Siqueira
2025-07-31 9:43 ` Timur Kristóf [this message]
2025-08-04 15:59 ` [PATCH 7/7] drm/amd/display: Fix fractional fb divider in set_pixel_clock_v3 Alex Deucher
2025-08-12 23:46 ` Rodrigo Siqueira
2025-08-09 20:25 ` [PATCH 0/7] DC: don't overclock DCE 6-10 and other fixes Timur Kristóf
2025-08-18 3:01 ` Alex Hung
2025-08-18 14:44 ` Alex Deucher
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