Re: [PATCH 01/10] drm/i915: Add support for mapping an object page by page

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On 04/02/16 09:30, ankitprasad.r.sharma@xxxxxxxxx wrote:
From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>

Introduced a new vm specfic callback insert_page() to program a single pte in
ggtt or ppgtt. This allows us to map a single page in to the mappable aperture
space. This can be iterated over to access the whole object by using space as
meagre as page size.

v2: Added low level rpm assertions to insert_page routines (Chris)

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@xxxxxxxxx>
---
  drivers/char/agp/intel-gtt.c        |  9 +++++
  drivers/gpu/drm/i915/i915_gem_gtt.c | 65 +++++++++++++++++++++++++++++++++++++
  drivers/gpu/drm/i915/i915_gem_gtt.h |  5 +++
  include/drm/intel-gtt.h             |  3 ++
  4 files changed, 82 insertions(+)

diff --git a/drivers/char/agp/intel-gtt.c b/drivers/char/agp/intel-gtt.c
index 1341a94..7c68576 100644
--- a/drivers/char/agp/intel-gtt.c
+++ b/drivers/char/agp/intel-gtt.c
@@ -838,6 +838,15 @@ static bool i830_check_flags(unsigned int flags)
  	return false;
  }

+void intel_gtt_insert_page(dma_addr_t addr,
+			   unsigned int pg,
+			   unsigned int flags)
+{
+	intel_private.driver->write_entry(addr, pg, flags);
+	wmb();
+}
+EXPORT_SYMBOL(intel_gtt_insert_page);
+
  void intel_gtt_insert_sg_entries(struct sg_table *st,
  				 unsigned int pg_start,
  				 unsigned int flags)
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 715a771..a64018f 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -2341,6 +2341,28 @@ static void gen8_set_pte(void __iomem *addr, gen8_pte_t pte)
  #endif
  }

+static void gen8_ggtt_insert_page(struct i915_address_space *vm,
+				  dma_addr_t addr,
+				  uint64_t offset,
+				  enum i915_cache_level level,
+				  u32 unused)
+{
+	struct drm_i915_private *dev_priv = to_i915(vm->dev);
+	gen8_pte_t __iomem *pte =
+		(gen8_pte_t __iomem *)dev_priv->gtt.gsm +
+		(offset >> PAGE_SHIFT);
+	int rpm_atomic_seq;
+
+	rpm_atomic_seq = assert_rpm_atomic_begin(dev_priv);
+
+	gen8_set_pte(pte, gen8_pte_encode(addr, level, true));
+	wmb();

gen8_ggtt_insert_entries does a read-back of the PTE after having written it with a big fat comment talking about how that could be really important. This is not needed in this path?

+
+	I915_WRITE(GFX_FLSH_CNTL_GEN6, GFX_FLSH_CNTL_EN);

Why is the posting read not required here as in gen8_ggtt_insert_entries?

+
+	assert_rpm_atomic_end(dev_priv, rpm_atomic_seq);
+}
+
  static void gen8_ggtt_insert_entries(struct i915_address_space *vm,
  				     struct sg_table *st,
  				     uint64_t start,
@@ -2412,6 +2434,28 @@ static void gen8_ggtt_insert_entries__BKL(struct i915_address_space *vm,
  	stop_machine(gen8_ggtt_insert_entries__cb, &arg, NULL);
  }

+static void gen6_ggtt_insert_page(struct i915_address_space *vm,
+				  dma_addr_t addr,
+				  uint64_t offset,
+				  enum i915_cache_level level,
+				  u32 flags)
+{
+	struct drm_i915_private *dev_priv = to_i915(vm->dev);
+	gen6_pte_t __iomem *pte =
+		(gen6_pte_t __iomem *)dev_priv->gtt.gsm +
+		(offset >> PAGE_SHIFT);
+	int rpm_atomic_seq;
+
+	rpm_atomic_seq = assert_rpm_atomic_begin(dev_priv);
+
+	iowrite32(vm->pte_encode(addr, level, true, flags), pte);
+	wmb();
+
+	I915_WRITE(GFX_FLSH_CNTL_GEN6, GFX_FLSH_CNTL_EN);
+
+	assert_rpm_atomic_end(dev_priv, rpm_atomic_seq);
+}

Same questions as for the gen8 version.

Regards,

Tvrtko
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