drm/i915: Check if the stolen memory "reserved" area is enabled or not

Apparently there are some machines that put semi-sensible looking values
into the stolen "reserved" base and size, except those values are actually
outside the stolen memory. There is a bit in the register which
supposedly could tell us whether the reserved area is even enabled or
not. Let's check for that before we go trusting the base and size.

Cc: Tomi Sarvela <tomi.p.sarvela@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171102151737.23336-1-ville.syrjala@linux.intel.comReviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -294,6 +294,12 @@ static void g4x_get_stolen_reserved(struct drm_i915_private *dev_priv,
 				     ELK_STOLEN_RESERVED);
 	dma_addr_t stolen_top = dev_priv->mm.stolen_base + ggtt->stolen_size;
 
+	if ((reg_val & G4X_STOLEN_RESERVED_ENABLE) == 0) {
+		*base = 0;
+		*size = 0;
+		return;
+	}
+
 	*base = (reg_val & G4X_STOLEN_RESERVED_ADDR2_MASK) << 16;
 
 	WARN_ON((reg_val & G4X_STOLEN_RESERVED_ADDR1_MASK) < *base);
@@ -313,6 +319,12 @@ static void gen6_get_stolen_reserved(struct drm_i915_private *dev_priv,
 {
 	uint32_t reg_val = I915_READ(GEN6_STOLEN_RESERVED);
 
+	if ((reg_val & GEN6_STOLEN_RESERVED_ENABLE) == 0) {
+		*base = 0;
+		*size = 0;
+		return;
+	}
+
 	*base = reg_val & GEN6_STOLEN_RESERVED_ADDR_MASK;
 
 	switch (reg_val & GEN6_STOLEN_RESERVED_SIZE_MASK) {
@@ -339,6 +351,12 @@ static void gen7_get_stolen_reserved(struct drm_i915_private *dev_priv,
 {
 	uint32_t reg_val = I915_READ(GEN6_STOLEN_RESERVED);
 
+	if ((reg_val & GEN6_STOLEN_RESERVED_ENABLE) == 0) {
+		*base = 0;
+		*size = 0;
+		return;
+	}
+
 	*base = reg_val & GEN7_STOLEN_RESERVED_ADDR_MASK;
 
 	switch (reg_val & GEN7_STOLEN_RESERVED_SIZE_MASK) {
@@ -359,6 +377,12 @@ static void chv_get_stolen_reserved(struct drm_i915_private *dev_priv,
 {
 	uint32_t reg_val = I915_READ(GEN6_STOLEN_RESERVED);
 
+	if ((reg_val & GEN6_STOLEN_RESERVED_ENABLE) == 0) {
+		*base = 0;
+		*size = 0;
+		return;
+	}
+
 	*base = reg_val & GEN6_STOLEN_RESERVED_ADDR_MASK;
 
 	switch (reg_val & GEN8_STOLEN_RESERVED_SIZE_MASK) {
@@ -387,6 +411,12 @@ static void bdw_get_stolen_reserved(struct drm_i915_private *dev_priv,
 	uint32_t reg_val = I915_READ(GEN6_STOLEN_RESERVED);
 	dma_addr_t stolen_top;
 
+	if ((reg_val & GEN6_STOLEN_RESERVED_ENABLE) == 0) {
+		*base = 0;
+		*size = 0;
+		return;
+	}
+
 	stolen_top = dev_priv->mm.stolen_base + ggtt->stolen_size;
 
 	*base = reg_val & GEN6_STOLEN_RESERVED_ADDR_MASK;

drivers/gpu/drm/i915/i915_reg.h

@@ -379,6 +379,7 @@ static inline bool i915_mmio_reg_valid(i915_reg_t reg)
 #define GEN8_STOLEN_RESERVED_2M		(1 << 7)
 #define GEN8_STOLEN_RESERVED_4M		(2 << 7)
 #define GEN8_STOLEN_RESERVED_8M		(3 << 7)
+#define GEN6_STOLEN_RESERVED_ENABLE	(1 << 0)
 
 /* VGA stuff */
 
@@ -3431,6 +3432,7 @@ enum i915_power_well_id {
 #define ELK_STOLEN_RESERVED		_MMIO(MCHBAR_MIRROR_BASE + 0x48)
 #define G4X_STOLEN_RESERVED_ADDR1_MASK	(0xFFFF << 16)
 #define G4X_STOLEN_RESERVED_ADDR2_MASK	(0xFFF << 4)
+#define G4X_STOLEN_RESERVED_ENABLE	(1 << 0)
 
 /* Memory controller frequency in MCHBAR for Haswell (possible SNB+) */
 #define DCLK _MMIO(MCHBAR_MIRROR_BASE_SNB + 0x5e04)