drm/i915: turn on small BAR support

With the uAPI in place we should now have enough in place to ensure a
working system on small BAR configurations.

v2: (Nirmoy & Thomas):
  - s/full BAR/Resizable BAR/ which is hopefully more easily
    understood by users.
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Jon Bloomfield <jon.bloomfield@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Kenneth Graunke <kenneth@whitecape.org>
Cc: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220629174350.384910-13-matthew.auld@intel.com

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

@@ -112,12 +112,6 @@ static struct intel_memory_region *setup_lmem(struct intel_gt *gt)
 		flat_ccs_base = intel_gt_mcr_read_any(gt, XEHP_FLAT_CCS_BASE_ADDR);
 		flat_ccs_base = (flat_ccs_base >> XEHP_CCS_BASE_SHIFT) * SZ_64K;
 
-		/* FIXME: Remove this when we have small-bar enabled */
-		if (pci_resource_len(pdev, 2) < lmem_size) {
-			drm_err(&i915->drm, "System requires small-BAR support, which is currently unsupported on this kernel\n");
-			return ERR_PTR(-EINVAL);
-		}
-
 		if (GEM_WARN_ON(lmem_size < flat_ccs_base))
 			return ERR_PTR(-EIO);
 
@@ -170,6 +164,10 @@ static struct intel_memory_region *setup_lmem(struct intel_gt *gt)
 	drm_info(&i915->drm, "Local memory available: %pa\n",
 		 &lmem_size);
 
+	if (io_size < lmem_size)
+		drm_info(&i915->drm, "Using a reduced BAR size of %lluMiB. Consider enabling 'Resizable BAR' or similar, if available in the BIOS.\n",
+			 (u64)io_size >> 20);
+
 	return mem;
 
 err_region_put: