Hi,
On Thu, 2016-02-11 at 10:50 +0000, Tvrtko Ursulin wrote:
>
> 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?
As per our discussion with Chris, wmb() is faster than doing a memory
access for reading the PTE.
So, I guess a barrier here should be better to keep things in sync.
>
> > +
> > + I915_WRITE(GFX_FLSH_CNTL_GEN6, GFX_FLSH_CNTL_EN);
>
> Why is the posting read not required here as in gen8_ggtt_insert_entries?
I agree with this, a POSTING_READ is required.
>
> > +
> > + 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
Thanks,
Ankit
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