drm/i915: Implement stolen reserved detection for ctg/elk

Finally managed to dig up enough hints as to where the stolen
reserved stuff lives on ctg/elk. So add the code to decode it.
This was a combination of old chipset specs, diggin up an old
elk grits release with an ctg/elk AubLoad etc.

This was only tested on an elk as I don't have a ctg here
unfortunately.

This leaves ilk as the only platform that doesn't have a way
to detect this stuff. Looking at the register contents on my
ilk, it might be that the elk way works there too, but I
can't be sure since I can't affect the amount of reserved
memory on that machine, and if I am to trust the register
contents, by default it would reserve 0 bytes.

v2: s/WARN_ON_ONCE/WARN_ON/ since it's in one time init code
    anyway (Paulo)

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -196,6 +196,29 @@ void i915_gem_cleanup_stolen(struct drm_device *dev)
 	drm_mm_takedown(&dev_priv->mm.stolen);
 }
 
+static void g4x_get_stolen_reserved(struct drm_i915_private *dev_priv,
+				    unsigned long *base, unsigned long *size)
+{
+	uint32_t reg_val = I915_READ(IS_GM45(dev_priv) ?
+				     CTG_STOLEN_RESERVED :
+				     ELK_STOLEN_RESERVED);
+	unsigned long stolen_top = dev_priv->mm.stolen_base +
+		dev_priv->gtt.stolen_size;
+
+	*base = (reg_val & G4X_STOLEN_RESERVED_ADDR2_MASK) << 16;
+
+	WARN_ON((reg_val & G4X_STOLEN_RESERVED_ADDR1_MASK) < *base);
+
+	/* 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;
+}
+
 static void gen6_get_stolen_reserved(struct drm_i915_private *dev_priv,
 				     unsigned long *base, unsigned long *size)
 {
@@ -315,10 +338,12 @@ int i915_gem_init_stolen(struct drm_device *dev)
 	switch (INTEL_INFO(dev_priv)->gen) {
 	case 2:
 	case 3:
+		break;
 	case 4:
-		if (!IS_G4X(dev))
-			break;
-		/* fall through */
+		if (IS_G4X(dev))
+			g4x_get_stolen_reserved(dev_priv, &reserved_base,
+						&reserved_size);
+		break;
 	case 5:
 		/* Assume the gen6 maximum for the older platforms. */
 		reserved_size = 1024 * 1024;

drivers/gpu/drm/i915/i915_reg.h

@@ -2494,6 +2494,11 @@ enum skl_disp_power_wells {
 
 #define MCHBAR_MIRROR_BASE_SNB	0x140000
 
+#define CTG_STOLEN_RESERVED		(MCHBAR_MIRROR_BASE + 0x34)
+#define ELK_STOLEN_RESERVED		(MCHBAR_MIRROR_BASE + 0x48)
+#define G4X_STOLEN_RESERVED_ADDR1_MASK	(0xFFFF << 16)
+#define G4X_STOLEN_RESERVED_ADDR2_MASK	(0xFFF << 4)
+
 /* Memory controller frequency in MCHBAR for Haswell (possible SNB+) */
 #define DCLK (MCHBAR_MIRROR_BASE_SNB + 0x5e04)