[PATCH AUTOSEL 6.16-6.6] drm/amd/display: Avoid configuring PSR granularity if PSR-SU not supported

[Sasha Levin <sashal@kernel.org>]

From: Mario Limonciello <mario.limonciello@amd.com>

[ Upstream commit a5ce8695d6d1b40d6960d2d298b579042c158f25 ]

[Why]
If PSR-SU is disabled on the link, then configuring su_y granularity in
mod_power_calc_psr_configs() can lead to assertions in
psr_su_set_dsc_slice_height().

[How]
Check the PSR version in amdgpu_dm_link_setup_psr() to determine whether
or not to configure granularity.

Reviewed-by: Sun peng (Leo) Li <sunpeng.li@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Ivan Lipski <ivan.lipski@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Now I have a clear understanding of the issue. Let me analyze the
commit:

## Analysis Summary

**Backport Status: YES**

## Extensive Explanation

This commit fixes a bug that can cause assertions (kernel
warnings/panics) in AMD display driver code when PSR (Panel Self
Refresh) is enabled on systems that don't support PSR-SU (Selective
Update).

### The Bug Being Fixed:

1. **Root Cause**: In `amdgpu_dm_link_setup_psr()`, the function
   `mod_power_calc_psr_configs()` is called for any PSR version (line
   113), which sets `psr_config->su_y_granularity` from DPCD
   capabilities (line 926 in power_helpers.c).

2. **The Problem**: Even when PSR-SU is not supported (PSR version 1),
   `psr_su_set_dsc_slice_height()` was being called unconditionally
   (line 122). This function contains an assertion check at lines
   968-970 that validates:
  ```c
  if (config->su_y_granularity &&
  (slice_height % config->su_y_granularity)) {
  ASSERT(0);
  return false;
  }
  ```

3. **Impact**: When PSR version 1 (non-SU) is active but
   `su_y_granularity` is non-zero from DPCD caps, the assertion
   triggers, potentially causing system instability or crashes.

### The Fix:

The commit adds a simple version check to only call
`psr_su_set_dsc_slice_height()` when PSR-SU (DC_PSR_VERSION_SU_1) is
actually supported:

```c
if (link->psr_settings.psr_version == DC_PSR_VERSION_SU_1) {
    if (!psr_su_set_dsc_slice_height(dc, link, stream, &psr_config))
        return false;
}
```

### Why This Should Be Backported:

1. **Bug Fix**: This fixes a real bug that causes assertions/warnings in
   production systems
2. **Small and Contained**: The fix is minimal - just adding a version
   check around an existing function call
3. **No Architectural Changes**: This doesn't introduce new features or
   change architecture
4. **Prevents System Instability**: Assertions in kernel code can lead
   to panics or unstable behavior
5. **Clear Regression Prevention**: Systems with PSR version 1 that have
   non-zero su_y_granularity values from their panel DPCD would hit this
   assertion
6. **Limited Scope**: Only affects AMD GPU display driver PSR
   functionality
7. **Safe Fix**: The change only adds a guard to prevent calling PSR-SU
   specific code when PSR-SU is not supported - this is clearly the
   correct behavior

The commit follows stable kernel rules perfectly - it's a targeted bug
fix that prevents potential system crashes without introducing new
functionality or risks.

 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_psr.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_psr.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_psr.c
index f984cb0cb889..ff7b867ae98b 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_psr.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_psr.c
@@ -119,8 +119,10 @@ bool amdgpu_dm_link_setup_psr(struct dc_stream_state *stream)
 		psr_config.allow_multi_disp_optimizations =
 			(amdgpu_dc_feature_mask & DC_PSR_ALLOW_MULTI_DISP_OPT);
 
-		if (!psr_su_set_dsc_slice_height(dc, link, stream, &psr_config))
-			return false;
+		if (link->psr_settings.psr_version == DC_PSR_VERSION_SU_1) {
+			if (!psr_su_set_dsc_slice_height(dc, link, stream, &psr_config))
+				return false;
+		}
 
 		ret = dc_link_setup_psr(link, stream, &psr_config, &psr_context);
 
-- 
2.39.5