[Intel-gfx] [PATCH 1/2] drm/i915: Do not cover all future platforms in TLB invalidation

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Revert to the original explicit approach and document the reasoning
behind it.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
---
 drivers/gpu/drm/i915/gt/intel_gt.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/intel_gt.c
index 7eeee5a7cb33..854841a731cb 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt.c
@@ -1070,7 +1070,18 @@ static void mmio_invalidate_full(struct intel_gt *gt)
 	unsigned int num = 0;
 	unsigned long flags;
 
-	if (GRAPHICS_VER_FULL(i915) >= IP_VER(12, 50)) {
+	/*
+	 * New platforms should not be added with catch-all-newer (>=)
+	 * condition so that any later platform added triggers the below warning
+	 * and in turn mandates a human cross-check of whether the invalidation
+	 * flows have compatible semantics.
+	 *
+	 * For instance with the 11.00 -> 12.00 transition three out of five
+	 * respective engine registers were moved to masked type. Then after the
+	 * 12.00 -> 12.50 transition multi cast handling is required too.
+	 */
+
+	if (GRAPHICS_VER_FULL(i915) == IP_VER(12, 50)) {
 		regs = NULL;
 		num = ARRAY_SIZE(xehp_regs);
 	} else if (GRAPHICS_VER(i915) == 12) {
-- 
2.34.1