drm/i915: Add missing mask when reading GEN12_DSMBASE

DSMBASE register is defined so BDSM bitfield contains the bits 63 to 20
of the base address of stolen. For the supported platforms bits 0-19 are
zero but that may not be true in future. Add the missing mask.

v2: Use REG_GENMASK64()
Acked-by: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Reviewed-by: Caz Yokoyama <caz@caztech.com>
Reviewed-by: Wayne Boyer <wayne.boyer@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220915-stolen-v2-1-20ff797de047@intel.com

drivers/gpu/drm/i915/gem/i915_gem_stolen.c

@@ -809,7 +809,7 @@ i915_gem_stolen_lmem_setup(struct drm_i915_private *i915, u16 type,
 		return ERR_PTR(-ENODEV);
 
 	/* Use DSM base address instead for stolen memory */
-	dsm_base = intel_uncore_read64(uncore, GEN12_DSMBASE);
+	dsm_base = intel_uncore_read64(uncore, GEN12_DSMBASE) & GEN12_BDSM_MASK;
 	if (IS_DG1(uncore->i915)) {
 		lmem_size = pci_resource_len(pdev, 2);
 		if (WARN_ON(lmem_size < dsm_base))

drivers/gpu/drm/i915/i915_reg.h

@@ -8501,6 +8501,7 @@ enum skl_power_gate {
 
 #define GEN12_GSMBASE			_MMIO(0x108100)
 #define GEN12_DSMBASE			_MMIO(0x1080C0)
+#define   GEN12_BDSM_MASK		REG_GENMASK64(63, 20)
 
 #define XEHP_CLOCK_GATE_DIS		_MMIO(0x101014)
 #define   SGSI_SIDECLK_DIS		REG_BIT(17)