From: Clay King <[email protected]> [ Upstream commit 7d9ec9dc20ecdb1661f4538cd9112cd3d6a5f15a ]
[Why] For RGB BT2020 full and limited color spaces, overlay adjustments were applied twice (once by MM and once by DAL). This results in incorrect colours and a noticeable difference between mpo and non-mpo cases. [How] Add RGB BT2020 full and limited color spaces to list that bypasses post csc adjustment. Reviewed-by: Aric Cyr <[email protected]> Signed-off-by: Clay King <[email protected]> Signed-off-by: Tom Chung <[email protected]> Signed-off-by: Alex Deucher <[email protected]> Signed-off-by: Sasha Levin <[email protected]> --- LLM Generated explanations, may be completely bogus: ## Analysis ### What the Commit Fixes This commit fixes a **color correctness bug** in AMD display driver for DCN3.0+ hardware. The bug causes incorrect colors when BT2020 RGB content is displayed with multi-plane overlay (MPO). **Root cause**: The old logic used a numeric enum comparison `color_space >= COLOR_SPACE_YCBCR601` to decide whether to apply ICSC or bypass post-CSC. Looking at the enum values: | Color Space | Value | Should Bypass? | Old Behavior | |---|---|---|---| | COLOR_SPACE_SRGB | 1 | YES | bypass (correct) | | COLOR_SPACE_MSREF_SCRGB | 4 | YES | bypass (correct) | | COLOR_SPACE_YCBCR601 | 5 | NO | ICSC (correct) | | COLOR_SPACE_2020_RGB_FULLRANGE | 11 | **YES** | **ICSC (WRONG)** | | COLOR_SPACE_2020_RGB_LIMITEDRANGE | 12 | **YES** | **ICSC (WRONG)** | Since `COLOR_SPACE_2020_RGB_FULLRANGE` (11) and `COLOR_SPACE_2020_RGB_LIMITEDRANGE` (12) are numerically >= `COLOR_SPACE_YCBCR601` (5), the old code incorrectly applied ICSC instead of bypassing post-CSC. This resulted in overlay adjustments being applied twice (by MM and DAL), causing visibly wrong colors in MPO vs non-MPO rendering. ### Fix Approach The fix replaces the fragile numeric comparison with an explicit switch- case function `dpp3_should_bypass_post_csc_for_colorspace()` that enumerates all RGB color spaces that should bypass post CSC. This is both a bug fix and a robustness improvement — future enum additions won't silently break the logic. ### Stable Kernel Criteria Assessment 1. **Fixes a real bug**: Yes — visible color corruption for BT2020 RGB content with MPO 2. **Obviously correct**: Yes — the switch-case explicitly lists RGB color spaces; reviewed by AMD's display lead (Aric Cyr) 3. **Small and contained**: Yes — ~30 lines added across 3 files, all in the same subsystem 4. **No new features**: Correct — this only fixes existing color space handling 5. **Risk**: Low — the change only affects which color spaces bypass post-CSC; worst case is reverting to the same incorrect behavior ### Concerns for Backporting - **dcn401_dpp.c** was introduced in April 2024 (kernel ~6.10), so this portion won't apply to older stable trees (6.6.y, 6.1.y, etc.). The dcn30 portion should apply to kernels with DCN3.0 support (5.8+). - **dcn10 and dcn20** have the same buggy pattern but are NOT fixed by this commit. This is not a blocker for backporting — the dcn30/dcn401 fix stands on its own. - The file paths were refactored in Feb 2024 (from `dc/dcn30/` to `dc/dpp/dcn30/`), so the patch will need path adjustment for older stable trees. ### User Impact Users with AMD GPUs (RDNA2+) displaying HDR/BT2020 RGB content see incorrect colors when the compositor uses multi-plane overlay. This is a real-world visual bug affecting desktop and media playback scenarios. ### Verification - Verified enum `dc_color_space` in `dc_hw_types.h` lines 642-666: confirmed `COLOR_SPACE_2020_RGB_FULLRANGE=11` and `COLOR_SPACE_2020_RGB_LIMITEDRANGE=12` are both >= `COLOR_SPACE_YCBCR601=5`, confirming the bug mechanism - Verified the same buggy pattern `color_space >= COLOR_SPACE_YCBCR601` exists in dcn10_dpp.c (line 398), dcn20_dpp.c (line 239), dcn30_dpp.c (line 379), and dcn401_dpp.c (line 209) — confirming this is a long- standing bug - Verified dcn401_dpp.c was introduced April 2024 (commit `70839da6360500a`), limiting backport applicability for dcn401 portion to kernels >= ~6.10 - Verified dcn30_dpp.c was moved to current path Feb 2024 — older stable trees will have it at `dc/dcn30/dcn30_dpp.c` - Verified the new function `dpp3_should_bypass_post_csc_for_colorspace` does not exist in the current tree yet (this commit introduces it), confirming no dependency issues - Could NOT verify whether specific user bug reports exist on mailing lists (unverified, but the commit message describes concrete user- visible symptoms) ### Summary This is a clear bug fix for visible color corruption affecting AMD display users with BT2020 RGB content. The fix is small, well-reviewed, and low-risk. The only backporting consideration is path adjustments for older stable trees and the dcn401 portion only applying to recent kernels. **YES** .../drm/amd/display/dc/dpp/dcn30/dcn30_dpp.c | 21 ++++++++++++++++--- .../drm/amd/display/dc/dpp/dcn30/dcn30_dpp.h | 4 ++++ .../amd/display/dc/dpp/dcn401/dcn401_dpp.c | 6 +++--- 3 files changed, 25 insertions(+), 6 deletions(-) diff --git a/drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.c b/drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.c index ef4a161171814..c7923531da83d 100644 --- a/drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.c +++ b/drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.c @@ -376,10 +376,10 @@ void dpp3_cnv_setup ( tbl_entry.color_space = input_color_space; - if (color_space >= COLOR_SPACE_YCBCR601) - select = INPUT_CSC_SELECT_ICSC; - else + if (dpp3_should_bypass_post_csc_for_colorspace(color_space)) select = INPUT_CSC_SELECT_BYPASS; + else + select = INPUT_CSC_SELECT_ICSC; dpp3_program_post_csc(dpp_base, color_space, select, &tbl_entry); @@ -1541,3 +1541,18 @@ bool dpp3_construct( return true; } +bool dpp3_should_bypass_post_csc_for_colorspace(enum dc_color_space dc_color_space) +{ + switch (dc_color_space) { + case COLOR_SPACE_UNKNOWN: + case COLOR_SPACE_SRGB: + case COLOR_SPACE_XR_RGB: + case COLOR_SPACE_SRGB_LIMITED: + case COLOR_SPACE_MSREF_SCRGB: + case COLOR_SPACE_2020_RGB_FULLRANGE: + case COLOR_SPACE_2020_RGB_LIMITEDRANGE: + return true; + default: + return false; + } +} diff --git a/drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.h b/drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.h index d4a70b4379eaf..6a61b99d6a798 100644 --- a/drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.h +++ b/drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.h @@ -644,4 +644,8 @@ void dpp3_program_cm_dealpha( void dpp3_cm_get_gamut_remap(struct dpp *dpp_base, struct dpp_grph_csc_adjustment *adjust); + +bool dpp3_should_bypass_post_csc_for_colorspace( + enum dc_color_space dc_color_space); + #endif /* __DC_HWSS_DCN30_H__ */ diff --git a/drivers/gpu/drm/amd/display/dc/dpp/dcn401/dcn401_dpp.c b/drivers/gpu/drm/amd/display/dc/dpp/dcn401/dcn401_dpp.c index 96c2c853de42c..2d6a646462e21 100644 --- a/drivers/gpu/drm/amd/display/dc/dpp/dcn401/dcn401_dpp.c +++ b/drivers/gpu/drm/amd/display/dc/dpp/dcn401/dcn401_dpp.c @@ -206,10 +206,10 @@ void dpp401_dpp_setup( tbl_entry.color_space = input_color_space; - if (color_space >= COLOR_SPACE_YCBCR601) - select = INPUT_CSC_SELECT_ICSC; - else + if (dpp3_should_bypass_post_csc_for_colorspace(color_space)) select = INPUT_CSC_SELECT_BYPASS; + else + select = INPUT_CSC_SELECT_ICSC; dpp3_program_post_csc(dpp_base, color_space, select, &tbl_entry); -- 2.51.0
