drm/i915/gt: limit lmem allocation size to succeed on SmallBars

In case system is short on mappable memory (256MB on SmallBar) allocation
of two 1GB buffers will fail.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/8300
Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230601144450.792228-1-andrzej.hajda@intel.com

Author: ahajda

drivers/gpu/drm/i915/gt/selftest_tlb.c

@@ -190,11 +190,18 @@ pte_tlbinv(struct intel_context *ce,
 
 static struct drm_i915_gem_object *create_lmem(struct intel_gt *gt)
 {
+	struct intel_memory_region *mr = gt->i915->mm.regions[INTEL_REGION_LMEM_0];
+	resource_size_t size = SZ_1G;
+
 	/*
 	 * Allocation of largest possible page size allows to test all types
-	 * of pages.
+	 * of pages. To succeed with both allocations, especially in case of Small
+	 * BAR, try to allocate no more than quarter of mappable memory.
 	 */
-	return i915_gem_object_create_lmem(gt->i915, SZ_1G, I915_BO_ALLOC_CONTIGUOUS);
+	if (mr && size > mr->io_size / 4)
+		size = mr->io_size / 4;
+
+	return i915_gem_object_create_lmem(gt->i915, size, I915_BO_ALLOC_CONTIGUOUS);
 }
 
 static struct drm_i915_gem_object *create_smem(struct intel_gt *gt)