From ecdde1779f97e59809aa743ecbf09d85c2b92884 Mon Sep 17 00:00:00 2001
From: Matt Roper <matthew.d.roper@intel.com>
Date: Tue, 12 Oct 2021 15:12:45 -0700
Subject: drm/i915/uapi: Add comment clarifying purpose of I915_TILING_* values
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Git-commit: ea673f17ab7638793a8b9e7fe04b4cb758fa01f1
Patch-mainline: v5.16-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225
The I915_TILING_* values in our uapi header are intended solely for use
with the old get_tiling/set_tiling ioctls that operate on hardware
de-tiling fences; all other uapi communication about tiling types is
done via framebuffer modifiers rather than with these old values.
On newer Intel platforms detiling fences no longer exist so the old
get_tiling/set_tiling ioctls are no longer usable and will always return
-EOPNOTSUPP. This means there's no reason to add new tiling types (such
as the Tile4 format introduced by Xe_HP) to the uapi header here. Any
kernel-internal code that needs to represent tiling format should either
rely on framebuffer modifiers (as the display code does) or use some
kind of non-uapi enum (as the GEM blt selftest now does).
References: https://patchwork.freedesktop.org/patch/456656/?series=95308
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Caz Yokoyama <caz.yokoyama@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211012221245.2609670-1-matthew.d.roper@intel.com
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
include/uapi/drm/i915_drm.h | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index aa2a7eccfb94..9b8e61163c39 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1522,6 +1522,12 @@ struct drm_i915_gem_caching {
#define I915_TILING_NONE 0
#define I915_TILING_X 1
#define I915_TILING_Y 2
+/*
+ * Do not add new tiling types here. The I915_TILING_* values are for
+ * de-tiling fence registers that no longer exist on modern platforms. Although
+ * the hardware may support new types of tiling in general (e.g., Tile4), we
+ * do not need to add them to the uapi that is specific to now-defunct ioctls.
+ */
#define I915_TILING_LAST I915_TILING_Y
#define I915_BIT_6_SWIZZLE_NONE 0
--
2.38.1