[PATCH AUTOSEL 6.17-6.12] drm/xe/guc: Increase GuC crash dump buffer size

[Sasha Levin <sashal@kernel.org>]

From: Zhanjun Dong <zhanjun.dong@intel.com>

[ Upstream commit ad83b1da5b786ee2d245e41ce55cb1c71fed7c22 ]

There are platforms already have a maximum dump size of 12KB, to avoid
data truncating, increase GuC crash dump buffer size to 16KB.

Signed-off-by: Zhanjun Dong <zhanjun.dong@intel.com>
Reviewed-by: Stuart Summers <stuart.summers@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://lore.kernel.org/r/20250829160427.1245732-1-zhanjun.dong@intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES

- What changed
  - The non-debug GuC crash log buffer was doubled from 8 KB to 16 KB by
    changing `CRASH_BUFFER_SIZE` from `SZ_8K` to `SZ_16K` in
    drivers/gpu/drm/xe/xe_guc_log.h:20. Debug builds remain unchanged at
    1 MB (drivers/gpu/drm/xe/xe_guc_log.h:16).

- Why it matters (bugfix, not a feature)
  - Commit message states some platforms produce up to 12 KB crash
    dumps; with an 8 KB buffer this causes truncation. That’s a
    functional defect in diagnostics: incomplete crash logs hinder
    debugging and postmortem analysis. Increasing to 16 KB fixes this
    truncation.

- Containment and safety
  - The size is consumed by the GuC CTL log parameter field using 4 KB
    units unless the size is a multiple of 1 MB. With 16 KB, the unit
    remains 4 KB and the value is encoded via `FIELD_PREP(GUC_LOG_CRASH,
    CRASH_BUFFER_SIZE / LOG_UNIT - 1)` in
    drivers/gpu/drm/xe/xe_guc.c:128, with `LOG_UNIT` set to `SZ_4K` for
    this case (drivers/gpu/drm/xe/xe_guc.c:101-107).
  - The GuC register field for the crash buffer size is 2 bits
    (`GUC_LOG_CRASH` is `REG_GENMASK(5, 4)`,
    drivers/gpu/drm/xe/xe_guc_fwif.h:94), encoding sizes of 4 KB, 8 KB,
    12 KB, and 16 KB. Setting 16 KB is the maximum representable and
    safely covers platforms needing 12 KB without truncation.
  - Compile-time checks enforce correctness and alignment:
    `BUILD_BUG_ON(!IS_ALIGNED(CRASH_BUFFER_SIZE, LOG_UNIT));` in
    drivers/gpu/drm/xe/xe_guc.c:118. 16 KB is aligned to 4 KB, so it
    passes.
  - The total BO allocation for logs increases by only 8 KB via
    `guc_log_size()` (drivers/gpu/drm/xe/xe_guc_log.c:61), which is
    negligible and localized to this driver. No ABI/API changes.
  - The change does not affect debug builds (`CONFIG_DRM_XE_DEBUG_GUC`),
    which already use 1 MB (drivers/gpu/drm/xe/xe_guc_log.h:16).

- Impact scope
  - Only the Intel Xe driver’s GuC logging path is affected. No
    architectural changes, no critical core subsystems touched. Memory
    impact is minimal and bounded per GT/tile.

- Stable criteria assessment
  - Fixes a real user-facing issue (truncated GuC crash dumps) that
    impairs diagnostics.
  - Small, contained change to a single constant; low regression risk.
  - No new features; no behavioral change beyond preventing truncation.
  - Aligns with hardware encodings and existing compile-time guards.

Given the clear bugfix nature, minimal risk, and confined scope, this is
a good candidate for stable backporting.

 drivers/gpu/drm/xe/xe_guc_log.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_guc_log.h b/drivers/gpu/drm/xe/xe_guc_log.h
index f1e2b0be90a9f..98a47ac42b08f 100644
--- a/drivers/gpu/drm/xe/xe_guc_log.h
+++ b/drivers/gpu/drm/xe/xe_guc_log.h
@@ -17,7 +17,7 @@ struct xe_device;
 #define DEBUG_BUFFER_SIZE       SZ_8M
 #define CAPTURE_BUFFER_SIZE     SZ_2M
 #else
-#define CRASH_BUFFER_SIZE	SZ_8K
+#define CRASH_BUFFER_SIZE	SZ_16K
 #define DEBUG_BUFFER_SIZE	SZ_64K
 #define CAPTURE_BUFFER_SIZE	SZ_1M
 #endif
-- 
2.51.0