[PATCH AUTOSEL 6.18-6.6] drm/amd/display: Fix DP no audio issue

[Sasha Levin <sashal@kernel.org>]

From: Charlene Liu <Charlene.Liu@amd.com>

[ Upstream commit 3886b198bd6e49c801fe9552fcfbfc387a49fbbc ]

[why]
need to enable APG_CLOCK_ENABLE enable first
also need to wake up az from D3 before access az block

Reviewed-by: Swapnil Patel <swapnil.patel@amd.com>
Signed-off-by: Charlene Liu <Charlene.Liu@amd.com>
Signed-off-by: Chenyu Chen <chen-yu.chen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit bf5e396957acafd46003318965500914d5f4edfa)
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

### 3. TECHNICAL ANALYSIS

**The Bug:**
The original code had an incorrect operation sequence:
1. Called `az_enable()` - attempts to access audio controller registers
2. Called `enable_pme_wa()` - wakes audio controller from D3 power state

This is backwards - you cannot access hardware registers while the
device is still in D3 (sleeping). The hardware must be woken up FIRST.

**The Fix:**
The fix simply reorders these operations:
1. Call `enable_pme_wa()` - wake audio controller from D3 first
2. Call `az_enable()` - now safe to access registers

### 4. SCOPE AND RISK ASSESSMENT

- **Lines changed:** ~8 lines (just reordering)
- **Files touched:** 1 file (dce110_hwseq.c)
- **Complexity:** Very low - no new logic, just reordering existing
  function calls
- **Subsystem:** AMD display driver, well-tested and mature
- **Risk:** Minimal - same operations, correct sequence

### 5. USER IMPACT

- **Affected users:** AMD GPU users with DisplayPort audio output
- **Severity:** High - complete loss of audio functionality
- **Usage scenario:** Very common (monitors with speakers, AV receivers,
  docking stations)
- **Symptoms:** "DP no audio issue" - a clearly user-visible bug

### 6. STABILITY INDICATORS

- Reviewed-by: Swapnil Patel (AMD engineer)
- Tested-by: Daniel Wheeler (AMD engineer)
- Multiple sign-offs from AMD display team
- Cherry-picked from mainline - indicates AMD considers it important

### 7. DEPENDENCY CHECK

The dce110_hwseq.c file has been in the kernel for years and the
`dce110_enable_audio_stream` function is stable code. The fix only
reorders existing calls to `enable_pme_wa()` and `az_enable()` - both of
which already exist in stable trees.

## Summary

**Meets stable criteria:**
- ✅ **Obviously correct:** Simple reordering to match hardware
  requirements
- ✅ **Fixes real bug:** Complete audio failure on DisplayPort is a
  significant user-visible bug
- ✅ **Small and contained:** ~8 lines changed, same functions, just
  different order
- ✅ **No new features:** No new functionality added
- ✅ **Tested:** Has Tested-by and Reviewed-by tags from AMD engineers
- ✅ **No dependencies:** Uses existing functions already in stable trees

**Risk vs Benefit:**
- **Benefit:** Restores DisplayPort audio functionality for affected AMD
  GPU users
- **Risk:** Very low - the same operations are performed, just in the
  correct hardware-required sequence

This is an ideal stable backport candidate: a small, surgical fix for a
clear user-visible bug (no audio on DP), with proper code review and
testing from the hardware vendor.

**YES**

 drivers/gpu/drm/amd/display/dc/hwss/dce110/dce110_hwseq.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/hwss/dce110/dce110_hwseq.c b/drivers/gpu/drm/amd/display/dc/hwss/dce110/dce110_hwseq.c
index ebc220b29d14..0bf98d834e61 100644
--- a/drivers/gpu/drm/amd/display/dc/hwss/dce110/dce110_hwseq.c
+++ b/drivers/gpu/drm/amd/display/dc/hwss/dce110/dce110_hwseq.c
@@ -1098,13 +1098,13 @@ void dce110_enable_audio_stream(struct pipe_ctx *pipe_ctx)
 			if (dc->current_state->res_ctx.pipe_ctx[i].stream_res.audio != NULL)
 				num_audio++;
 		}
+		if (num_audio >= 1 && clk_mgr->funcs->enable_pme_wa) {
+			/*wake AZ from D3 first before access az endpoint*/
+			clk_mgr->funcs->enable_pme_wa(clk_mgr);
+		}
 
 		pipe_ctx->stream_res.audio->funcs->az_enable(pipe_ctx->stream_res.audio);
 
-		if (num_audio >= 1 && clk_mgr->funcs->enable_pme_wa)
-			/*this is the first audio. apply the PME w/a in order to wake AZ from D3*/
-			clk_mgr->funcs->enable_pme_wa(clk_mgr);
-
 		link_hwss->enable_audio_packet(pipe_ctx);
 
 		if (pipe_ctx->stream_res.audio)
-- 
2.51.0