[PATCH 1/4] drm/xe: Add build on bug to assert page fault queue works

[Matthew Brost <matthew.brost@intel.com>]

If NUM_PF_QUEUE % PF_MSG_LEN_DW != 0 then the page fault queue logic
does not work when wrapping occurs. Add a build bug on to assert
NUM_PF_QUEUE % PF_MSG_LEN_DW == 0 to enforce this restriction and
document the code.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
---
 drivers/gpu/drm/xe/xe_gt_pagefault.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_gt_pagefault.c b/drivers/gpu/drm/xe/xe_gt_pagefault.c
index 4489aadc7a52..16cea47d9e15 100644
--- a/drivers/gpu/drm/xe/xe_gt_pagefault.c
+++ b/drivers/gpu/drm/xe/xe_gt_pagefault.c
@@ -328,6 +328,11 @@ int xe_guc_pagefault_handler(struct xe_guc *guc, u32 *msg, u32 len)
 	u32 asid;
 	bool full;
 
+	/*
+	 * The below logic doesn't work unless NUM_PF_QUEUE % PF_MSG_LEN_DW == 0
+	 */
+	BUILD_BUG_ON(NUM_PF_QUEUE % PF_MSG_LEN_DW);
+
 	if (unlikely(len != PF_MSG_LEN_DW))
 		return -EPROTO;
 
-- 
2.34.1