drm/i915: fix stolen bios_reserved checks

I started digging this when I noticed that the BDW code was just
reserving 1mb by coincidence since it was reading reserved fields.
Then I noticed we didn't have any values set for SNB and earlier, and
that the HSW sizes were wrong. After that, I noticed that the reserved
area has a specific start, and may not exactly end where the stolen
memory ends. I also noticed the base pointer can be zero. So I decided
to just write a single patch fixing everything instead of 20 patches
that would be much harder to review.

This patch may solve random stolen memory corruption/problems on
almost all platforms. Notice that since this is always dealing with
the top of the stolen memory, the problems are not so easy to
reproduce - especially since FBC is still disabled by default.

One of the major differences of this patch is that we now look at both
the size and base address. By only looking at the size we were
assuming that the reserved area was always at the very top of
stolen, which is not always true.

After we merge the patch series that allows user space to allocate
stolen memory we'll be able to write IGT tests that maybe catch the
bugs fixed by this patch.

v2:
  - s/BIOS reserved/stolen reserved/g (Chris)
  - Don't DRM_ERROR if we can't do anything about it (Chris)
  - Improve debug messages (Chris).
  - Use the gen7 version instead of gen6 on HSW. Tom found some
    documentation problems, so I think with gen7 we're on the safer
    side (Tom).
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -186,11 +186,103 @@ void i915_gem_cleanup_stolen(struct drm_device *dev)
 	drm_mm_takedown(&dev_priv->mm.stolen);
 }
 
+static void gen6_get_stolen_reserved(struct drm_i915_private *dev_priv,
+				     unsigned long *base, unsigned long *size)
+{
+	uint32_t reg_val = I915_READ(GEN6_STOLEN_RESERVED);
+
+	*base = reg_val & GEN6_STOLEN_RESERVED_ADDR_MASK;
+
+	switch (reg_val & GEN6_STOLEN_RESERVED_SIZE_MASK) {
+	case GEN6_STOLEN_RESERVED_1M:
+		*size = 1024 * 1024;
+		break;
+	case GEN6_STOLEN_RESERVED_512K:
+		*size = 512 * 1024;
+		break;
+	case GEN6_STOLEN_RESERVED_256K:
+		*size = 256 * 1024;
+		break;
+	case GEN6_STOLEN_RESERVED_128K:
+		*size = 128 * 1024;
+		break;
+	default:
+		*size = 1024 * 1024;
+		MISSING_CASE(reg_val & GEN6_STOLEN_RESERVED_SIZE_MASK);
+	}
+}
+
+static void gen7_get_stolen_reserved(struct drm_i915_private *dev_priv,
+				     unsigned long *base, unsigned long *size)
+{
+	uint32_t reg_val = I915_READ(GEN6_STOLEN_RESERVED);
+
+	*base = reg_val & GEN7_STOLEN_RESERVED_ADDR_MASK;
+
+	switch (reg_val & GEN7_STOLEN_RESERVED_SIZE_MASK) {
+	case GEN7_STOLEN_RESERVED_1M:
+		*size = 1024 * 1024;
+		break;
+	case GEN7_STOLEN_RESERVED_256K:
+		*size = 256 * 1024;
+		break;
+	default:
+		*size = 1024 * 1024;
+		MISSING_CASE(reg_val & GEN7_STOLEN_RESERVED_SIZE_MASK);
+	}
+}
+
+static void gen8_get_stolen_reserved(struct drm_i915_private *dev_priv,
+				     unsigned long *base, unsigned long *size)
+{
+	uint32_t reg_val = I915_READ(GEN6_STOLEN_RESERVED);
+
+	*base = reg_val & GEN6_STOLEN_RESERVED_ADDR_MASK;
+
+	switch (reg_val & GEN8_STOLEN_RESERVED_SIZE_MASK) {
+	case GEN8_STOLEN_RESERVED_1M:
+		*size = 1024 * 1024;
+		break;
+	case GEN8_STOLEN_RESERVED_2M:
+		*size = 2 * 1024 * 1024;
+		break;
+	case GEN8_STOLEN_RESERVED_4M:
+		*size = 4 * 1024 * 1024;
+		break;
+	case GEN8_STOLEN_RESERVED_8M:
+		*size = 8 * 1024 * 1024;
+		break;
+	default:
+		*size = 8 * 1024 * 1024;
+		MISSING_CASE(reg_val & GEN8_STOLEN_RESERVED_SIZE_MASK);
+	}
+}
+
+static void bdw_get_stolen_reserved(struct drm_i915_private *dev_priv,
+				    unsigned long *base, unsigned long *size)
+{
+	uint32_t reg_val = I915_READ(GEN6_STOLEN_RESERVED);
+	unsigned long stolen_top;
+
+	stolen_top = dev_priv->mm.stolen_base + dev_priv->gtt.stolen_size;
+
+	*base = reg_val & GEN6_STOLEN_RESERVED_ADDR_MASK;
+
+	/* On these platforms, the register doesn't have a size field, so the
+	 * size is the distance between the base and the top of the stolen
+	 * memory. We also have the genuine case where base is zero and there's
+	 * nothing reserved. */
+	if (*base == 0)
+		*size = 0;
+	else
+		*size = stolen_top - *base;
+}
+
 int i915_gem_init_stolen(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	u32 tmp;
-	int bios_reserved = 0;
+	unsigned long reserved_total, reserved_base, reserved_size;
+	unsigned long stolen_top;
 
 	mutex_init(&dev_priv->mm.stolen_lock);
 
@@ -208,26 +300,61 @@ int i915_gem_init_stolen(struct drm_device *dev)
 	if (dev_priv->mm.stolen_base == 0)
 		return 0;
 
-	DRM_DEBUG_KMS("found %zd bytes of stolen memory at %08lx\n",
-		      dev_priv->gtt.stolen_size, dev_priv->mm.stolen_base);
-
-	if (INTEL_INFO(dev)->gen >= 8) {
-		tmp = I915_READ(GEN7_BIOS_RESERVED);
-		tmp >>= GEN8_BIOS_RESERVED_SHIFT;
-		tmp &= GEN8_BIOS_RESERVED_MASK;
-		bios_reserved = (1024*1024) << tmp;
-	} else if (IS_GEN7(dev)) {
-		tmp = I915_READ(GEN7_BIOS_RESERVED);
-		bios_reserved = tmp & GEN7_BIOS_RESERVED_256K ?
-			256*1024 : 1024*1024;
+	stolen_top = dev_priv->mm.stolen_base + dev_priv->gtt.stolen_size;
+
+	switch (INTEL_INFO(dev_priv)->gen) {
+	case 2:
+	case 3:
+	case 4:
+	case 5:
+		/* Assume the gen6 maximum for the older platforms. */
+		reserved_size = 1024 * 1024;
+		reserved_base = stolen_top - reserved_size;
+		break;
+	case 6:
+		gen6_get_stolen_reserved(dev_priv, &reserved_base,
+					 &reserved_size);
+		break;
+	case 7:
+		gen7_get_stolen_reserved(dev_priv, &reserved_base,
+					 &reserved_size);
+		break;
+	default:
+		if (IS_BROADWELL(dev_priv) || IS_SKYLAKE(dev_priv))
+			bdw_get_stolen_reserved(dev_priv, &reserved_base,
+						&reserved_size);
+		else
+			gen8_get_stolen_reserved(dev_priv, &reserved_base,
+						 &reserved_size);
+		break;
+	}
+
+	/* It is possible for the reserved base to be zero, but the register
+	 * field for size doesn't have a zero option. */
+	if (reserved_base == 0) {
+		reserved_size = 0;
+		reserved_base = stolen_top;
 	}
 
-	if (WARN_ON(bios_reserved > dev_priv->gtt.stolen_size))
+	if (reserved_base < dev_priv->mm.stolen_base ||
+	    reserved_base + reserved_size > stolen_top) {
+		DRM_DEBUG_KMS("Stolen reserved area [0x%08lx - 0x%08lx] outside stolen memory [0x%08lx - 0x%08lx]\n",
+			      reserved_base, reserved_base + reserved_size,
+			      dev_priv->mm.stolen_base, stolen_top);
 		return 0;
+	}
+
+	/* It is possible for the reserved area to end before the end of stolen
+	 * memory, so just consider the start. */
+	reserved_total = stolen_top - reserved_base;
+
+	DRM_DEBUG_KMS("Memory reserved for graphics device: %luK, usable: %luK\n",
+		      dev_priv->gtt.stolen_size >> 10,
+		      (dev_priv->gtt.stolen_size - reserved_total) >> 10);
 
 	/* Basic memrange allocator for stolen space */
 	drm_mm_init(&dev_priv->mm.stolen, 0, dev_priv->gtt.stolen_size -
-		    bios_reserved);
+		    reserved_total);
 
 	return 0;
 }

drivers/gpu/drm/i915/i915_reg.h

@@ -178,13 +178,22 @@
 #define GAB_CTL				0x24000
 #define   GAB_CTL_CONT_AFTER_PAGEFAULT	(1<<8)
 
-#define GEN7_BIOS_RESERVED		0x1082C0
-#define GEN7_BIOS_RESERVED_1M		(0 << 5)
-#define GEN7_BIOS_RESERVED_256K		(1 << 5)
-#define GEN8_BIOS_RESERVED_SHIFT       7
-#define GEN7_BIOS_RESERVED_MASK        0x1
-#define GEN8_BIOS_RESERVED_MASK        0x3
-
+#define GEN6_STOLEN_RESERVED		0x1082C0
+#define GEN6_STOLEN_RESERVED_ADDR_MASK	(0xFFF << 20)
+#define GEN7_STOLEN_RESERVED_ADDR_MASK	(0x3FFF << 18)
+#define GEN6_STOLEN_RESERVED_SIZE_MASK	(3 << 4)
+#define GEN6_STOLEN_RESERVED_1M		(0 << 4)
+#define GEN6_STOLEN_RESERVED_512K	(1 << 4)
+#define GEN6_STOLEN_RESERVED_256K	(2 << 4)
+#define GEN6_STOLEN_RESERVED_128K	(3 << 4)
+#define GEN7_STOLEN_RESERVED_SIZE_MASK	(1 << 5)
+#define GEN7_STOLEN_RESERVED_1M		(0 << 5)
+#define GEN7_STOLEN_RESERVED_256K	(1 << 5)
+#define GEN8_STOLEN_RESERVED_SIZE_MASK	(3 << 7)
+#define GEN8_STOLEN_RESERVED_1M		(0 << 7)
+#define GEN8_STOLEN_RESERVED_2M		(1 << 7)
+#define GEN8_STOLEN_RESERVED_4M		(2 << 7)
+#define GEN8_STOLEN_RESERVED_8M		(3 << 7)
 
 /* VGA stuff */