[PATCH] drm/i915/mtl: Fix MTL stolen memory GGTT mapping

[Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>]

The PTEs expect the offset from the base of the fake LMEM region (i.e.
the base of stolen) and not from the base of the DSM. Quoting the specs:
"Driver will set the Device Memory bit = 1 in the PTE when pointing to a
page in DSM and program the PTE with offset from LMEM_BAR. Device Memory
Offset from LMEM_BAR is same as offset from BGSM."

DSM starts 8MBs from BGSM, so we set dsm_base = 8MB.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Cc: Fei Yang <fei.yang@intel.com>
Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
---

I've omitted the fixes tag from the commit message since MTL is still
under force_probe, so there isn't really any need to propagate the fixes,
but here it is for reference:

Fixes: dbb2ffbfd708 ("drm/i915/mtl: enable local stolen memory")

 drivers/gpu/drm/i915/gem/i915_gem_stolen.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
index d8e06e783e30..8ac376c24aa2 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
@@ -890,8 +890,9 @@ i915_gem_stolen_lmem_setup(struct drm_i915_private *i915, u16 type,
 	if (HAS_LMEMBAR_SMEM_STOLEN(i915)) {
 		/*
 		 * MTL dsm size is in GGC register.
-		 * Also MTL uses offset to DSMBASE in ptes, so i915
-		 * uses dsm_base = 0 to setup stolen region.
+		 * Also MTL uses offset to GSMBASE in ptes, so i915
+		 * uses dsm_base = 8MBs to setup stolen region, since
+		 * DSMBASE = GSMBASE + 8MB.
 		 */
 		ret = mtl_get_gms_size(uncore);
 		if (ret < 0) {
@@ -899,11 +900,11 @@ i915_gem_stolen_lmem_setup(struct drm_i915_private *i915, u16 type,
 			return ERR_PTR(ret);
 		}
 
-		dsm_base = 0;
+		dsm_base = SZ_8M;
 		dsm_size = (resource_size_t)(ret * SZ_1M);
 
 		GEM_BUG_ON(pci_resource_len(pdev, GEN12_LMEM_BAR) != SZ_256M);
-		GEM_BUG_ON((dsm_size + SZ_8M) > lmem_size);
+		GEM_BUG_ON((dsm_base + dsm_size) > lmem_size);
 	} else {
 		/* Use DSM base address instead for stolen memory */
 		dsm_base = intel_uncore_read64(uncore, GEN12_DSMBASE) & GEN12_BDSM_MASK;
@@ -912,14 +913,12 @@ i915_gem_stolen_lmem_setup(struct drm_i915_private *i915, u16 type,
 		dsm_size = ALIGN_DOWN(lmem_size - dsm_base, SZ_1M);
 	}
 
-	io_size = dsm_size;
-	if (HAS_LMEMBAR_SMEM_STOLEN(i915)) {
-		io_start = pci_resource_start(pdev, GEN12_LMEM_BAR) + SZ_8M;
-	} else if (pci_resource_len(pdev, GEN12_LMEM_BAR) < lmem_size) {
+	if (pci_resource_len(pdev, GEN12_LMEM_BAR) < lmem_size) {
 		io_start = 0;
 		io_size = 0;
 	} else {
 		io_start = pci_resource_start(pdev, GEN12_LMEM_BAR) + dsm_base;
+		io_size = dsm_size;
 	}
 
 	min_page_size = HAS_64K_PAGES(i915) ? I915_GTT_PAGE_SIZE_64K :
-- 
2.37.3