[Intel-gfx] [PATCH] i915: Drop relocation support on all new hardware

[Jason Ekstrand]

The Vulkan driver in Mesa for Intel hardware never uses relocations if
it's running on a version of i915 that supports at least softpin which
all versions of i915 supporting Gen12 do.  On the OpenGL side, Gen12+ is
only supported by iris which never uses relocations.  The older i965
driver in Mesa does use relocations but it only supports Intel hardware
through Gen11 and has been deprecated for all hardware Gen9+.  The
compute driver also never uses relocations.  This only leaves the media
driver which is supposed to be switching to softpin going forward.
Making softpin a requirement for all future hardware seems reasonable.

Rejecting relocations starting with Gen12 has the benefit that we don't
have to bother supporting it on platforms with local memory.  Given how
much CPU touching of memory is required for relocations, not having to
do so on platforms where not all memory is directly CPU-accessible
carries significant advantages.

Signed-off-by: Jason Ekstrand <jason at jlekstrand.net>
Cc: Dave Airlie <airlied at redhat.com>
Cc: Daniel Vetter <daniel.vetter at intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 99772f37bff60..de093acb7721c 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -1764,7 +1764,8 @@ eb_relocate_vma_slow(struct i915_execbuffer *eb, struct eb_vma *ev)
 	return err;
 }
 
-static int check_relocations(const struct drm_i915_gem_exec_object2 *entry)
+static int check_relocations(const struct i915_execbuffer *eb,
+			     const struct drm_i915_gem_exec_object2 *entry)
 {
 	const char __user *addr, *end;
 	unsigned long size;
@@ -1774,6 +1775,13 @@ static int check_relocations(const struct drm_i915_gem_exec_object2 *entry)
 	if (size == 0)
 		return 0;
 
+	/* Relocations are disallowed for all platforms after TGL-LP */
+	if (INTEL_GEN(eb->i915) >= 12 && !IS_TIGERLAKE(eb->i915))
+		return -EINVAL;
+
+	/* All discrete memory platforms are Gen12 or above */
+	BUG_ON(HAS_LMEM(eb->i915));
+
 	if (size > N_RELOC(ULONG_MAX))
 		return -EINVAL;
 
@@ -1807,7 +1815,7 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
 		if (nreloc == 0)
 			continue;
 
-		err = check_relocations(&eb->exec[i]);
+		err = check_relocations(eb, &eb->exec[i]);
 		if (err)
 			goto err;
 
@@ -1880,7 +1888,7 @@ static int eb_prefault_relocations(const struct i915_execbuffer *eb)
 	for (i = 0; i < count; i++) {
 		int err;
 
-		err = check_relocations(&eb->exec[i]);
+		err = check_relocations(eb, &eb->exec[i]);
 		if (err)
 			return err;
 	}
-- 
2.29.2