drm/xe: Carve out top of DSM as reserved

Top of DSM contains the WOPCM where kernel driver shouldn't access as
it contains data from other HW agents. Carve it out from the stolen
memory. On a MTL system, the output now matches the expected values:
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20230726160708.3967790-10-lucas.demarchi@intel.comSigned-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/regs/xe_regs.h

@@ -97,4 +97,7 @@
 #define DSMBASE					XE_REG(0x1080C0)
 #define   BDSM_MASK				REG_GENMASK64(63, 20)
 
+#define STOLEN_RESERVED				XE_REG(0x1082c0)
+#define   WOPCM_SIZE_MASK			REG_GENMASK64(8, 7)
+
 #endif

drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c

@@ -89,7 +89,7 @@ static s64 detect_bar2_dgfx(struct xe_device *xe, struct xe_ttm_stolen_mgr *mgr)
 static u32 detect_bar2_integrated(struct xe_device *xe, struct xe_ttm_stolen_mgr *mgr)
 {
 	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
-	u32 stolen_size;
+	u32 stolen_size, wopcm_size;
 	u32 ggc, gms;
 
 	ggc = xe_mmio_read32(xe_root_mmio_gt(xe), GGC);
@@ -124,6 +124,12 @@ static u32 detect_bar2_integrated(struct xe_device *xe, struct xe_ttm_stolen_mgr
 		return 0;
 	}
 
+	/* Carve out the top of DSM as it contains the reserved WOPCM region */
+	wopcm_size = REG_FIELD_GET64(WOPCM_SIZE_MASK,
+				     xe_mmio_read64(xe_root_mmio_gt(xe),
+						    STOLEN_RESERVED));
+	stolen_size -= (1U << wopcm_size) * SZ_1M;
+
 	if (drm_WARN_ON(&xe->drm, stolen_size + SZ_8M > pci_resource_len(pdev, 2)))
 		return 0;