[PATCH v2 04/15] drm/i915: Bypass LMEMBAR/GTTMMADR for MTL stolen memory access

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

On MTL accessing stolen memory via the BARs is somehow borked,
and it can hang the machine. As a workaround let's bypass the
BARs and just go straight to DSMBASE/GSMBASE instead.

Note that on every other platform this itself would hang the
machine, but on MTL the system firmware is expected to relax
the access permission guarding stolen memory to enable this
workaround, and thus direct CPU accesses should be fine.

TODO: add w/a numbers and whatnot

Cc: Paz Zcharya <pazz at chromium.org>
Cc: Nirmoy Das <nirmoy.das at intel.com>
Cc: Radhakrishna Sripada <radhakrishna.sripada at intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_stolen.c | 11 ++++++++++-
 drivers/gpu/drm/i915/gt/intel_ggtt.c       | 13 ++++++++++++-
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
index ee237043c302..252fe5cd6ede 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
@@ -941,7 +941,16 @@ i915_gem_stolen_lmem_setup(struct drm_i915_private *i915, u16 type,
 		dsm_size = ALIGN_DOWN(lmem_size - dsm_base, SZ_1M);
 	}
 
-	if (pci_resource_len(pdev, GEN12_LMEM_BAR) < lmem_size) {
+	if (IS_METEORLAKE(i915)) {
+		/*
+		 * Workaround: access via BAR can hang MTL, go directly to DSM.
+		 *
+		 * Normally this would not work but on MTL the system firmware
+		 * should have relaxed the access permissions sufficiently.
+		 */
+		io_start = intel_uncore_read64(uncore, GEN12_DSMBASE) & GEN12_BDSM_MASK;
+		io_size = dsm_size;
+	} else if (pci_resource_len(pdev, GEN12_LMEM_BAR) < lmem_size) {
 		io_start = 0;
 		io_size = 0;
 	} else {
diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c b/drivers/gpu/drm/i915/gt/intel_ggtt.c
index 21a7e3191c18..ab71d74ec426 100644
--- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
+++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
@@ -24,6 +24,7 @@
 #include "intel_ring.h"
 #include "i915_drv.h"
 #include "i915_pci.h"
+#include "i915_reg.h"
 #include "i915_request.h"
 #include "i915_scatterlist.h"
 #include "i915_utils.h"
@@ -1152,13 +1153,23 @@ static unsigned int gen6_gttadr_offset(struct drm_i915_private *i915)
 static int ggtt_probe_common(struct i915_ggtt *ggtt, u64 size)
 {
 	struct drm_i915_private *i915 = ggtt->vm.i915;
+	struct intel_uncore *uncore = ggtt->vm.gt->uncore;
 	struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
 	phys_addr_t phys_addr;
 	u32 pte_flags;
 	int ret;
 
 	GEM_WARN_ON(pci_resource_len(pdev, GEN4_GTTMMADR_BAR) != gen6_gttmmadr_size(i915));
-	phys_addr = pci_resource_start(pdev, GEN4_GTTMMADR_BAR) + gen6_gttadr_offset(i915);
+	/*
+	 * Workaround: access via BAR can hang MTL, go directly to GSM.
+	 *
+	 * Normally this would not work but on MTL the system firmware
+	 * should have relaxed the access permissions sufficiently.
+	 */
+	if (IS_METEORLAKE(i915))
+		phys_addr = intel_uncore_read64(uncore, GEN12_GSMBASE) & GEN12_BDSM_MASK;
+	else
+		phys_addr = pci_resource_start(pdev, GEN4_GTTMMADR_BAR) + gen6_gttadr_offset(i915);
 
 	if (needs_wc_ggtt_mapping(i915))
 		ggtt->gsm = ioremap_wc(phys_addr, size);
-- 
2.41.0