From: Gilles Risch <[email protected]> [ Upstream commit 275c3332585bbabcefad109a6978cc0cbecf2008 ]
The Apple iMac11,1 (27-inch, Late 2009) uses a Mobility Radeon HD 4850 (RV770/DCE3.1) with a 2560x1440 internal panel on an internal DisplayPort path. Without this fix the display stays dark under KMS. This machine suffers from the same issue as iMac10,1 and iMac11,2: Apple routes the internal display through Link B of the DIG encoder instead of Link A. Add iMac11,1 to the existing DMI quirk and move the Apple-specific encoder assignment into its own block, independent of the DCE version check. Additionally, the 2560x1440 panel requires RADEON_PLL_USE_FRAC_FB_DIV and ATOM_ENCODER_CMD_DP_VIDEO_ON, limited to iMac11,1 via dmi_match() to avoid affecting other boards. Reviewed-by: Lukas Wunner <[email protected]> Signed-off-by: Gilles Risch <[email protected]> Signed-off-by: Alex Deucher <[email protected]> Signed-off-by: Sasha Levin <[email protected]> --- LLM Generated explanations, may be completely bogus: The local tree is **6.12.111** (`pending-6.12`). The iMac11,1 Link-B quirk is missing here; iMac10,1 and iMac11,2 already have it. This is a DMI-limited hardware quirk that lights the internal panel, and it matches the stable exception for device-specific workarounds. =============================================================== PHASE 1: COMMIT MESSAGE FORENSICS =============================================================== **Step 1.1: PARSE THE SUBJECT LINE** Record: `[drm/radeon] [fix] internal display stays dark on iMac11,1 (RV770/DCE3.1)` **Step 1.2: PARSE ALL COMMIT MESSAGE TAGS** Record: - `Reviewed-by: Lukas Wunner <[email protected]>` - `Signed-off-by: Gilles Risch <[email protected]>` (author) - `Signed-off-by: Alex Deucher <[email protected]>` (radeon maintainer) - No `Fixes:` tag (expected) - No `Reported-by:` / `Tested-by:` / `Link:` / `Cc: stable` (expected for this review pipeline) - No syzbot / sanitizer tags **Step 1.3: ANALYZE THE COMMIT BODY TEXT** Record: - **Bug:** Apple iMac11,1 (27-inch, Late 2009) Mobility Radeon HD 4850 (RV770/DCE3.1), 2560x1440 internal panel on an internal DisplayPort path. - **Symptom:** Internal display stays dark under KMS. - **Root cause:** Same Apple Link-B DIG routing as iMac10,1 and iMac11,2; plus this 2560x1440 panel also needs `RADEON_PLL_USE_FRAC_FB_DIV` and `ATOM_ENCODER_CMD_DP_VIDEO_ON`. - **Fix approach:** Add iMac11,1 to the existing DMI quirk; move Apple encoder assignment out of the DCE-version check; DMI-limit the PLL and DP_VIDEO_ON extras to iMac11,1. - **Version info:** None in the message. Hardware is 2009; related quirks date to 2017/2023. **Step 1.4: DETECT HIDDEN BUG FIXES** Record: Not hidden. This is an explicit hardware-quirk bug fix (dark panel). Not cleanup, refactor, or a new API. =============================================================== PHASE 2: DIFF ANALYSIS - LINE BY LINE =============================================================== **Step 2.1: INVENTORY THE CHANGES** Record: - `drivers/gpu/drm/radeon/atombios_crtc.c`: +`#include <linux/dmi.h>`; PLL flag condition widened for iMac11,1 (~3 lines net) - `drivers/gpu/drm/radeon/atombios_encoders.c`: DP_VIDEO_ON DMI match; encoder picker restructure (~12 lines) - Functions: `atombios_adjust_pll()`, `radeon_atom_encoder_dpms_dig()`, `radeon_atom_pick_dig_encoder()` - Scope: small, two-file surgical driver quirk (~17 insertions / 11 deletions) **Step 2.2: UNDERSTAND THE CODE FLOW CHANGE** Record: 1. **PLL (`atombios_adjust_pll`):** Before, `RADEON_PLL_USE_FRAC_FB_DIV` for clocks >165 MHz only if `ASIC_IS_DCE32()`. After, also if DMI product is `iMac11,1`. RV770 is not DCE3.2 (`CHIP_RV770` precedes `CHIP_RV730`), so iMac11,1 never took this path. 2. **DPMS ON (`radeon_atom_encoder_dpms_dig`):** Before, `ATOM_ENCODER_CMD_DP_VIDEO_ON` only if `ASIC_IS_DCE4()`. After, also for iMac11,1. DCE3.1 iMac11,1 never issued VIDEO_ON. 3. **Encoder pick (`radeon_atom_pick_dig_encoder`):** Before, Apple Link-B assignment lived inside `if (ASIC_IS_DCE32())` for iMac10,1 and iMac11,2 only. iMac11,1 (DCE3.1) fell through to DCE3 LVTMA logic, which does not use `dig->linkb`. After, Apple DMI check runs first (now including iMac11,1), then DCE32 still uses `crtc_id`. iMac10,1/11,2 behavior is preserved. **Step 2.3: IDENTIFY THE BUG MECHANISM** Record: **[h] Hardware workaround / DMI quirk.** Wrong DIG encoder (Link A vs Link B), missing fractional FB divider for a high-clock 2560x1440 panel, missing DP video-on ATOM command. Combined result: dark internal panel. **Step 2.4: ASSESS THE FIX QUALITY** Record: - Quality: high. PLL and VIDEO_ON are DMI-limited. Encoder change for other Apple iMacs is behavior-preserving. Non-Apple DCE3.1 still uses the old LVTMA path. - Maintainer (Alex Deucher) rejected v4’s `ASIC_IS_DCE31()` because it would change encoder routing for all DCE3.1 boards; v5 follows that request. - Residual: DPMS OFF still does not send `DP_VIDEO_OFF` for iMac11,1 (only DCE4+ does). That can only affect this one DMI product, and v5 dropped the broader resume/OFF series on purpose. - Regression risk: low. No public API, no lock, no refcount, no new module param. =============================================================== PHASE 3: GIT HISTORY INVESTIGATION =============================================================== **Step 3.1: BLAME THE CHANGED LINES** Record: - PLL DCE32 check: `a02dc74b317d78` (Alex Deucher, 2012) “dce32+: use fractional fb dividers for high clocks” - DP_VIDEO_ON DCE4 check: `3f03ced8808792` (Alex Deucher, 2011) - Apple DMI quirk: `564d8a2cf3abf1` (Mario Kleiner, 2017, iMac10,1) then `05eacc198c68cb` (Mark Hawrylak, 2023, iMac11,2) - DCE32 encoder pick: `3f03ced8808792` (2011) - Bug is long-standing (pre-3.13 for the sibling iMac10,1 issue). Present in this 6.12 tree. **Step 3.2: FOLLOW THE FIXES: TAG** Record: No `Fixes:` tag. Closest ancestors in this tree: - `564d8a2cf3abf` “Fix eDP for single-display iMac10,1 (v2)” — `Cc: stable`, `git merge-base --is-ancestor` = yes - `05eacc198c68c` “Fix eDP for single-display iMac11,2” — `Cc: stable`, ancestor = yes Those two patches could not cover iMac11,1 because they are inside `ASIC_IS_DCE32()`, and RV770 is not DCE3.2. **Step 3.3: CHECK FILE HISTORY FOR RELATED CHANGES** Record: Recent radeon encoder/crtc history is backlight, helper conversions, iMac12,x backlight — not a conflicting refactor of this picker. Standalone v5 (earlier v3 was 2/2; resume patch was dropped). No missing prerequisite in this tree. **Step 3.4: CHECK THE AUTHOR'S OTHER COMMITS** Record: Gilles Risch has no radeon commits in this tree (first-time hardware reporter/tester). Alex Deucher is the radeon maintainer and signed off. Lukas Wunner (Apple/x86) reviewed. **Step 3.5: CHECK FOR DEPENDENT/PREREQUISITE COMMITS** Record: Uses existing `dmi_match()`, `RADEON_PLL_USE_FRAC_FB_DIV`, `ATOM_ENCODER_CMD_DP_VIDEO_ON`, `radeon_atom_pick_dig_encoder()`. Adds `#include <linux/dmi.h>` to `atombios_crtc.c` (not currently included; `atombios_encoders.c` already has it). Applies standalone. Companion eDP resume patch is not required for the boot-time dark-panel fix. =============================================================== PHASE 4: MAILING LIST AND EXTERNAL RESEARCH =============================================================== **Step 4.1: FIND THE ORIGINAL PATCH DISCUSSION** Record: - Candidate SHA is not in this tree, so `b4 dig -c <this-commit>` cannot be used. Located via subject search. - v5: https://lore.gitlab.freedesktop.org/drm-ai- reviews/[email protected]/ (Message-ID `[email protected]`) - v4 review (Alex): https://lists.freedesktop.org/archives/amd- gfx/2026-May/145586.html - Revisions: v1 (2026-05-10) → v2 → v3 0/2 (plus resume patch) → v4 (`ASIC_IS_DCE31`) → **v5** (DMI-only encoder block; this commit) - Alex NAK’d v4’s `if (ASIC_IS_DCE31())` as changing DCE3.1 routing generally; asked for an iMac11,1 DMI block with `goto assigned`. v5 does that (and includes the other two Apple DMI IDs). - No NAK on v5. No reviewer `Cc: stable` found. - `b4 mbox` of the v5 msgid started (30 messages) then failed on a local save path; thread content was retrieved via lore/gitlab and lists.freedesktop.org instead. **Step 4.2: CHECK WHO REVIEWED THE PATCH** Record: To: Alex Deucher. Cc: amd-gfx, dri-devel. Reviewed-by Lukas Wunner (on v2; tag kept). Applied/signed-off by Alex Deucher. **Step 4.3: SEARCH FOR THE BUG REPORT** Record: Author tested on a real iMac11,1. Symptom is dark KMS display. Same class as documented iMac10,1 (Mario Kleiner, 2017: black display when radeon KMS loads) and iMac11,2 (2023). A 2023 amd-gfx attempt (“Fix eDP for single-display iMac11,1”) used `ASIC_IS_DCE31` and did not land; this 2026 series is the one that did. **Step 4.4: CHECK FOR RELATED PATCHES AND SERIES** Record: v3 2/2 “fix eDP resume from suspend” (VIDEO_OFF + `atombios_set_edp_panel_power` for iMac11,1) was not part of v5. v5 is self-contained for initial bring-up. Not a hard dependency. **Step 4.5: CHECK STABLE MAILING LIST HISTORY** Record: UNVERIFIED — lore.kernel.org returned 403. Sibling iMac10,1 and iMac11,2 quirks both carried `Cc: [email protected]` and are in this tree. =============================================================== PHASE 5: CODE SEMANTIC ANALYSIS =============================================================== **Step 5.1: IDENTIFY KEY FUNCTIONS IN THE DIFF** Record: `atombios_adjust_pll`, `radeon_atom_encoder_dpms_dig`, `radeon_atom_pick_dig_encoder` **Step 5.2: TRACE CALLERS** Record: - `atombios_adjust_pll()` ← `atombios_crtc.c` mode-set (`radeon_crtc->adjusted_clock = atombios_adjust_pll(...)`) - `radeon_atom_pick_dig_encoder()` ← `radeon_atom_encoder_prepare()` (modeset prepare) ← `radeon_atom_dig_helper_funcs.prepare` - `radeon_atom_encoder_dpms_dig()` ← `radeon_atom_encoder_dpms()` for UNIPHY/LVTMA ← helper `.dpms`, `.commit` (DPMS_ON), `.disable` (DPMS_OFF) **Step 5.3: TRACE CALLEES** Record: `atombios_dig_encoder_setup()` / `atom_execute_table()` (ATOM BIOS), `radeon_dp_link_train()`, `dmi_match()`. No alloc/lock changes. **Step 5.4: FOLLOW THE CALL CHAIN** Record: Userspace DRM modeset / KMS bring-up on this iMac. Reachable on every graphical boot for that machine. Not a syscall fuzzer path; it is the normal display path. **Step 5.5: SEARCH FOR SIMILAR PATTERNS** Record: Same DMI Link-B pattern already used for iMac10,1 and iMac11,2 in this file. This commit extends that list and lifts it out of `ASIC_IS_DCE32()`. =============================================================== PHASE 6: CROSS-REFERENCING AGAINST THE LOCAL TREE =============================================================== **Step 6.1: DOES THE BUGGY CODE EXIST IN THIS TREE?** Record: Yes. `git describe HEAD` = `p-6.12-3-gc504cf0baa3d8`; `make kernelversion` = **6.12.111**. - `atombios_encoders.c:2130-2135` still matches only iMac10,1 / iMac11,2 inside `ASIC_IS_DCE32()`. - No `iMac11,1` in `drivers/gpu/drm/radeon/`. - `ASIC_IS_DCE32` = `family >= CHIP_RV730`; `radeon_family.h` has `CHIP_RV770` then `CHIP_RV730`, so RV770 is DCE3 but not DCE3.2. - Candidate commit is not an ancestor of HEAD. **Step 6.2: CHECK FOR BACKPORT COMPLICATIONS** Record: **Clean apply.** Pre-image in this tree matches the provided diff (PLL line 597, DPMS line 1710, picker 2125-2138). Need the new `linux/dmi.h` include in `atombios_crtc.c`. **Step 6.3: CHECK IF RELATED FIXES ARE ALREADY HERE** Record: iMac10,1 and iMac11,2 quirks are present. They do not cover iMac11,1. No alternate iMac11,1 radeon fix in this tree. =============================================================== PHASE 7: SUBSYSTEM AND MAINTAINER CONTEXT =============================================================== **Step 7.1: IDENTIFY THE SUBSYSTEM AND ITS CRITICALITY** Record: `[drm/radeon] [IMPORTANT]` — legacy AMD GPU KMS driver, still `CONFIG_DRM_RADEON` in this tree. Affects one Apple DMI product, not core mm/fs. **Step 7.2: ASSESS SUBSYSTEM ACTIVITY** Record: Mature/legacy. Occasional hardware quirks and small fixes. Encoder picker logic has been stable since ~2011 with Apple DMI additions in 2017 and 2023. =============================================================== PHASE 8: IMPACT AND RISK ASSESSMENT =============================================================== **Step 8.1: DETERMINE WHO IS AFFECTED** Record: Driver-specific + DMI-specific: Apple iMac11,1 (Late 2009 27-inch, HD 4850). Encoder restructure also runs on iMac10,1 and iMac11,2 with the same Link-B assignment they already had. **Step 8.2: DETERMINE THE TRIGGER CONDITIONS** Record: Loading radeon KMS / modesetting the internal panel. Common for anyone using this machine as a Linux desktop. Not a race. Unprivileged user does not need a special trigger beyond using the GUI. **Step 8.3: DETERMINE THE FAILURE MODE SEVERITY** Record: **[Dark internal display / unusable KMS console and desktop] [HIGH]** — not a panic, but the primary display does not work. Same severity as the iMac10,1/iMac11,2 quirks that went to stable. **Step 8.4: CALCULATE RISK-BENEFIT RATIO** Record: - Benefit: high for iMac11,1 6.12 LTS users (working internal panel). - Risk: very low (~20 lines, DMI-gated extras, behavior-preserving picker for existing Apple IDs). - Ratio: favors backport. =============================================================== PHASE 9: FINAL SYNTHESIS =============================================================== **Step 9.1: COMPILE THE EVIDENCE** FOR: - Real, user-visible bug: internal panel stays dark under KMS. - Hardware quirk exception (DMI table), same pattern as iMac10,1/iMac11,2 which had `Cc: stable` and are already in this tree. - Small, obviously correct after maintainer feedback (v5 vs rejected v4 `ASIC_IS_DCE31`). - DMI-limited PLL and VIDEO_ON so other RV770 boards are unchanged. - Buggy code exists in 6.12.111; patch applies cleanly. - Reviewed by Lukas Wunner; signed off by Alex Deucher; tested on the machine. AGAINST: - Not a crash, UAF, or CVE. - Affects one 2009 iMac model. - No matching `DP_VIDEO_OFF` (iMac11,1-only residual on DPMS off). - Resume/eDP power follow-up is a separate patch, not included. UNRESOLVED: - lore.kernel.org/stable search (HTTP 403). - `b4 dig` on the candidate SHA (commit not in this tree). - Whether a later VIDEO_OFF/resume patch exists upstream after v5. **Step 9.2: APPLY THE STABLE RULES CHECKLIST** 1. Obviously correct and tested? **PASS** — v5 matches maintainer request; tested on iMac11,1; Reviewed-by + maintainer SOB. 2. Fixes a real bug that affects users? **PASS** — dark KMS display on that iMac. 3. Important issue? **PASS** — unusable internal display; hardware-quirk class already accepted for the sibling iMacs. 4. Small and contained? **PASS** — two files, ~20 lines. 5. No new features or APIs? **PASS** — DMI quirk on existing driver paths. 6. Can apply to the local tree? **PASS** — context matches 6.12.111. **Step 9.3: CHECK FOR EXCEPTION CATEGORIES** Record: **Hardware quirk/workaround** (Apple DMI encoder/PLL/DP command). Explicitly allowed for stable. **Step 9.4: DECISION** This should be backported to this 6.12 tree. It is the same class of Apple radeon eDP quirk as iMac10,1 and iMac11,2, which this tree already carries. iMac11,1 is RV770/DCE3.1, so it never matched `ASIC_IS_DCE32()` and still boots with a dark panel. The fix is small, DMI-limited, applies cleanly, and was narrowed specifically so it does not retune other DCE3.1 boards. Verification: - [Phase 1] Parsed subject/tags/body from the provided commit; no Fixes/Cc-stable (expected). - [Phase 2] Diff: `atombios_adjust_pll` FRAC_FB_DIV, `radeon_atom_encoder_dpms_dig` DP_VIDEO_ON, `radeon_atom_pick_dig_encoder` DMI block moved out of DCE32. - [Phase 2] Confirmed local code at `atombios_encoders.c:1710` and `:2130-2135` and `atombios_crtc.c:597` matches the pre-image. - [Phase 3] `git blame`: PLL `a02dc74b317d78` (2012), VIDEO_ON `3f03ced8808792` (2011), Apple DMI `564d8a2cf3abf` (2017) / `05eacc198c68c` (2023). - [Phase 3] `git merge-base --is-ancestor` 564d8a2cf3abf and 05eacc198c68c vs HEAD: both present. - [Phase 3] `radeon_family.h`: CHIP_RV770 immediately before CHIP_RV730; `ASIC_IS_DCE32` is `>= CHIP_RV730`. - [Phase 3] No Gilles Risch radeon commits in this tree; Alex Deucher is the maintainer. - [Phase 4] v5 lore: Message-ID `[email protected]`. - [Phase 4] Alex v4 comment (lists.freedesktop.org/amd- gfx/2026-May/145586.html): do not use `ASIC_IS_DCE31()` for routing; use iMac11,1 `dmi_match` + `goto assigned`. - [Phase 4] Lukas Wunner Reviewed-by on v2 (ratatoskr.run/amd- gfx/2026/05/9273941). - [Phase 4] lore.kernel.org fetches: 403. UNVERIFIED: stable@ discussion. - [Phase 4] `b4 mbox` v5 msgid: 30 messages found, local save failed. UNVERIFIED: full mbox dump. - [Phase 5] Callers: `radeon_atom_encoder_prepare` → pick encoder; `radeon_atom_encoder_dpms` → UNIPHY dpms_dig; `atombios_adjust_pll` from CRTC mode set. - [Phase 6] `git describe HEAD` = p-6.12-3-gc504cf0baa3d8; `make kernelversion` = 6.12.111; `iMac11,1` absent from radeon/. - [Phase 8] Failure mode: dark internal panel on KMS load, severity HIGH for that DMI product. - UNVERIFIED: whether a post-v5 DP_VIDEO_OFF/resume patch later landed upstream. **YES** drivers/gpu/drm/radeon/atombios_crtc.c | 5 ++++- drivers/gpu/drm/radeon/atombios_encoders.c | 23 ++++++++++++---------- 2 files changed, 17 insertions(+), 11 deletions(-) diff --git a/drivers/gpu/drm/radeon/atombios_crtc.c b/drivers/gpu/drm/radeon/atombios_crtc.c index 9b3a3a9d60e20..837700ab8079f 100644 --- a/drivers/gpu/drm/radeon/atombios_crtc.c +++ b/drivers/gpu/drm/radeon/atombios_crtc.c @@ -24,6 +24,8 @@ * Alex Deucher */ +#include <linux/dmi.h> + #include <drm/drm_fixed.h> #include <drm/drm_fourcc.h> #include <drm/drm_framebuffer.h> @@ -594,7 +596,8 @@ static u32 atombios_adjust_pll(struct drm_crtc *crtc, if (((rdev->family == CHIP_RS780) || (rdev->family == CHIP_RS880)) && !radeon_crtc->ss_enabled) radeon_crtc->pll_flags |= RADEON_PLL_USE_FRAC_FB_DIV; - if (ASIC_IS_DCE32(rdev) && mode->clock > 165000) + if ((ASIC_IS_DCE32(rdev) || dmi_match(DMI_PRODUCT_NAME, "iMac11,1")) + && mode->clock > 165000) radeon_crtc->pll_flags |= RADEON_PLL_USE_FRAC_FB_DIV; } else { radeon_crtc->pll_flags |= RADEON_PLL_LEGACY; diff --git a/drivers/gpu/drm/radeon/atombios_encoders.c b/drivers/gpu/drm/radeon/atombios_encoders.c index 3d9f47bc807af..ddfa31a7b83a5 100644 --- a/drivers/gpu/drm/radeon/atombios_encoders.c +++ b/drivers/gpu/drm/radeon/atombios_encoders.c @@ -1707,7 +1707,7 @@ radeon_atom_encoder_dpms_dig(struct drm_encoder *encoder, int mode) if (ENCODER_MODE_IS_DP(atombios_get_encoder_mode(encoder)) && connector) { /* DP_SET_POWER_D0 is set in radeon_dp_link_train */ radeon_dp_link_train(encoder, connector); - if (ASIC_IS_DCE4(rdev)) + if (ASIC_IS_DCE4(rdev) || dmi_match(DMI_PRODUCT_NAME, "iMac11,1")) atombios_dig_encoder_setup(encoder, ATOM_ENCODER_CMD_DP_VIDEO_ON, 0); } if (radeon_encoder->devices & (ATOM_DEVICE_LCD_SUPPORT)) { @@ -2123,17 +2123,20 @@ int radeon_atom_pick_dig_encoder(struct drm_encoder *encoder, int fe_idx) } /* - * On DCE32 any encoder can drive any block so usually just use crtc id, - * but Apple thinks different at least on iMac10,1 and iMac11,2, so there use linkb, - * otherwise the internal eDP panel will stay dark. + * Apple routes the internal eDP panel through Link B of the DIG encoder + * instead of Link A on the iMac10,1, iMac11,1 and iMac11,2. + * Use linkb to avoid a dark display. */ - if (ASIC_IS_DCE32(rdev)) { - if (dmi_match(DMI_PRODUCT_NAME, "iMac10,1") || - dmi_match(DMI_PRODUCT_NAME, "iMac11,2")) - enc_idx = (dig->linkb) ? 1 : 0; - else - enc_idx = radeon_crtc->crtc_id; + if (dmi_match(DMI_PRODUCT_NAME, "iMac10,1") || + dmi_match(DMI_PRODUCT_NAME, "iMac11,1") || + dmi_match(DMI_PRODUCT_NAME, "iMac11,2")) { + enc_idx = (dig->linkb) ? 1 : 0; + goto assigned; + } + /* on DCE32 and encoder can driver any block so just crtc id */ + if (ASIC_IS_DCE32(rdev)) { + enc_idx = radeon_crtc->crtc_id; goto assigned; } -- 2.53.0
