[PATCH] drm/xe/rtp: Fix build error with clang < 21 and non-const initializers

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

Clang < 21 treats const-qualified compound literals at function scope as
having static storage duration, which requires all initializer elements
to be compile-time constants.  When xe_hw_engine.c initializes a local
struct xe_rtp_table_sr using XE_RTP_TABLE_SR(), the compound literals in
XE_RTP_TABLE_SR end up containing runtime values (e.g. blit_cctl_val
derived from gt->mocs.uc_index), triggering:

  xe_hw_engine.c:361: error: initializer element is not a compile-time constant
  xe_hw_engine.c:416: error: initializer element is not a compile-time constant

ARRAY_SIZE() cannot be used as a replacement because it expands through
__must_be_array() -> __BUILD_BUG_ON_ZERO_MSG() -> _Static_assert inside
sizeof(struct{}), which clang < 21 also rejects in the same context.

Replace ARRAY_SIZE() with an open-coded sizeof(arr)/sizeof(elem) in
XE_RTP_TABLE_SR and XE_RTP_TABLE to avoid both issues.

Fixes: 5ff004fdc737 ("drm/xe/rtp: Add struct types for RTP tables")
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Gustavo Sousa <gustavo.sousa@intel.com>
Cc: Violet Monti <violet.monti@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Cc: intel-xe@lists.freedesktop.org
Reported-by: Mark Brown <broonie@kernel.org>
Closes: https://lore.kernel.org/intel-xe/bfb0dee8-b243-47ba-a89d-71472b0d51c5@sirena.org.uk/
Assisted-by: GitHub_Copilot:claude-sonnet-4.6
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
---
 drivers/gpu/drm/xe/xe_rtp.h | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_rtp.h b/drivers/gpu/drm/xe/xe_rtp.h
index 4e3cfd69f922..2cc65053cd07 100644
--- a/drivers/gpu/drm/xe/xe_rtp.h
+++ b/drivers/gpu/drm/xe/xe_rtp.h
@@ -461,14 +461,22 @@ struct xe_reg_sr;
 		XE_RTP_PASTE_FOREACH(ACTION_, COMMA, (__VA_ARGS__))	\
 	}
 
+/*
+ * Note: ARRAY_SIZE() cannot be used here because it expands through
+ * __must_be_array() -> __BUILD_BUG_ON_ZERO_MSG() -> _Static_assert inside
+ * sizeof(struct{}), which clang < 21 rejects when the compound literal
+ * contains non-compile-time-constant initializers.
+ */
 #define XE_RTP_TABLE_SR(...) { \
 	.entries = (const struct xe_rtp_entry_sr[]){__VA_ARGS__}, \
-	.n_entries = ARRAY_SIZE(((const struct xe_rtp_entry_sr[]){__VA_ARGS__})), \
+	.n_entries = sizeof((const struct xe_rtp_entry_sr[]){__VA_ARGS__}) / \
+		sizeof(struct xe_rtp_entry_sr), \
 }
 
 #define XE_RTP_TABLE(...) { \
 	.entries = (const struct xe_rtp_entry[]){__VA_ARGS__}, \
-	.n_entries = ARRAY_SIZE(((const struct xe_rtp_entry[]){__VA_ARGS__})), \
+	.n_entries = sizeof((const struct xe_rtp_entry[]){__VA_ARGS__}) / \
+		sizeof(struct xe_rtp_entry), \
 }
 
 #define XE_RTP_PROCESS_CTX_INITIALIZER(arg__) _Generic((arg__),							\
-- 
2.54.0