[PATCH 21/62] [v4] drm/i915/bdw: Support BDW caching

Ben Widawsky
2013-11-05T03:56:52Z

BDW caching works differently than the previous generations. Instead of
having bits in the PTE which directly control how the page is cached,
the 3 PTE bits PWT PCD and PAT provide an index into a PAT defined by
register 0x40e0. This style of caching is functionally equivalent to how
it works on HSW and before.

v2: Tiny bikeshed as discussed on internal irc.

v3: Squash in patch from Ville to mirror the x86 PAT setup more like
in arch/x86/mm/pat.c. Primarily, the 0th index will be WB, and not
uncached.

v4: Comment for reason to not use a 64b write on the PPAT.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net> (v1)
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
drivers/gpu/drm/i915/i915_gem_gtt.c | 44 +++++++++++++++++++++++++++++++++++++
drivers/gpu/drm/i915/i915_reg.h | 1 +
2 files changed, 45 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index ff52c48..57b21c3 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -58,12 +58,21 @@ typedef uint64_t gen8_gtt_pte_t;
#define HSW_WB_ELLC_LLC_AGE0 HSW_CACHEABILITY_CONTROL(0xb)
#define HSW_WT_ELLC_LLC_AGE0 HSW_CACHEABILITY_CONTROL(0x6)

+#define PPAT_UNCACHED_INDEX (_PAGE_PWT | _PAGE_PCD)
+#define PPAT_CACHED_PDE_INDEX 0 /* WB LLC */
+#define PPAT_CACHED_INDEX _PAGE_PAT /* WB LLCeLLC */
+#define PPAT_DISPLAY_ELLC_INDEX _PAGE_PCD /* WT eLLC */
+
static inline gen8_gtt_pte_t gen8_pte_encode(dma_addr_t addr,
enum i915_cache_level level,
bool valid)
{
gen8_gtt_pte_t pte = valid ? _PAGE_PRESENT | _PAGE_RW : 0;
pte |= addr;
+ if (level != I915_CACHE_NONE)
+ pte |= PPAT_CACHED_INDEX;
+ else
+ pte |= PPAT_UNCACHED_INDEX;
return pte;
}

@@ -805,6 +814,7 @@ static void i915_gtt_color_adjust(struct drm_mm_node *node,
*end -= 4096;
}
}
+
void i915_gem_setup_global_gtt(struct drm_device *dev,
unsigned long start,
unsigned long mappable_end,
@@ -1002,6 +1012,38 @@ static int ggtt_probe_common(struct drm_device *dev,
return ret;
}

+/* The GGTT and PPGTT need a private PPAT setup in order to handle cacheability
+ * bits. When using advanced contexts each context stores its own PAT, but
+ * writing this data shouldn't be harmful even in those cases. */
+static void gen8_setup_private_ppat(struct drm_i915_private *dev_priv)
+{
+#define GEN8_PPAT_UC (0<<0)
+#define GEN8_PPAT_WC (1<<0)
+#define GEN8_PPAT_WT (2<<0)
+#define GEN8_PPAT_WB (3<<0)
+#define GEN8_PPAT_ELLC_OVERRIDE (0<<2)
+#define GEN8_PPAT_LLC (1<<2)
+#define GEN8_PPAT_LLCELLC (2<<2)
+#define GEN8_PPAT_LLCeLLC (3<<2) /* BSPEC mistake? */
+#define GEN8_PPAT_AGE(x) (x<<4)
+#define GEN8_PPAT(i, x) ((uint64_t) (x) << ((i) * 8))
+ uint64_t pat;
+
+ pat = GEN8_PPAT(0, GEN8_PPAT_WB | GEN8_PPAT_LLC) | /* for normal objects, no eLLC */
+ GEN8_PPAT(1, GEN8_PPAT_WC | GEN8_PPAT_LLCELLC) | /* for something pointing to ptes? */
+ GEN8_PPAT(2, GEN8_PPAT_WT | GEN8_PPAT_LLCELLC) | /* for scanout with eLLC */
+ GEN8_PPAT(3, GEN8_PPAT_UC) | /* Uncached objects, mostly for scanout */
+ GEN8_PPAT(4, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(0)) |
+ GEN8_PPAT(5, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(1)) |
+ GEN8_PPAT(6, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(2)) |
+ GEN8_PPAT(7, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(3));
+
+ /* XXX: spec defines this as 2 distinct registers. It's unclear if a 64b
+ * write would work. */
+ I915_WRITE(GEN8_PRIVATE_PAT, pat);
+ I915_WRITE(GEN8_PRIVATE_PAT + 4, pat >> 32);
+}
+
static int gen8_gmch_probe(struct drm_device *dev,
size_t *gtt_total,
size_t *stolen,
@@ -1027,6 +1069,8 @@ static int gen8_gmch_probe(struct drm_device *dev,
gtt_size = gen8_get_total_gtt_size(snb_gmch_ctl);
*gtt_total = (gtt_size / sizeof(gen8_gtt_pte_t)) << PAGE_SHIFT;

+ gen8_setup_private_ppat(dev_priv);
+
ret = ggtt_probe_common(dev, gtt_size);

dev_priv->gtt.base.clear_range = gen8_ggtt_clear_range;
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index b801b88..9929750 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -664,6 +664,7 @@
#define RING_FAULT_FAULT_TYPE(x) ((x >> 1) & 0x3)
#define RING_FAULT_VALID (1<<0)
#define DONE_REG 0x40b0
+#define GEN8_PRIVATE_PAT 0x40e0
#define BSD_HWS_PGA_GEN7 (0x04180)
#define BLT_HWS_PGA_GEN7 (0x04280)
#define VEBOX_HWS_PGA_GEN7 (0x04380)
--
1.8.4.2

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