On 09/03/16 11:09, akash.goel@xxxxxxxxx wrote:
From: Akash Goel <akash.goel@xxxxxxxxx>
A new libdrm interface 'drm_intel_gem_bo_map_wc' is provided by this
patch. Through this interface Gfx clients can create write combining
virtual mappings of the Gem object. It will provide the same funtionality
of 'mmap_gtt' interface without the constraints of limited aperture space,
but provided clients handles the linear to tile conversion on their own.
This patch is intended for improving the CPU write operation performance,
as with such mapping, writes are almost 50% faster than with mmap_gtt.
Also it avoids the Cache flush after update from CPU side, when object is
passed on to GPU, which will be the case if regular mmap interface is used.
This type of mapping is specially useful in case of sub-region
update, i.e. when only a portion of the object is to be updated.
Also there is a support for the unsynchronized version of this interface
named 'drm_intel_gem_bo_map_wc_unsynchronized', through which wc virtual
mappings, but unsynchronized one, can be created of the Gem object.
To ensure the cache coherency, before using this mapping, the GTT domain has
been reused here. This provides the required Cache flush if the object is in
CPU domain or synchronization against the concurrent rendering
The drm_i915_gem_mmap structure (for the DRM_I915_GEM_MMAP_IOCTL) has been
extended with a new flags field (defaulting to 0 for existent users). In
order for userspace to detect the extended ioctl, a new parameter
I915_PARAM_HAS_EXT_MMAP has been added for versioning the ioctl interface.
v2: Aligned with the v2 of the corresponding kernel patch (Chris)
v3: Added the unmap calls for the wc mapping (Damien)
Added the param feature check before creating the wc mapping & reduced
the vma limit (Chris)
v4: Removed the extraneous unlock call from map_wc function (Damien)
v5: Rebased.
Signed-off-by: Akash Goel <akash.goel@xxxxxxxxx>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Damien Lespiau <damien.lespiau@xxxxxxxxx>
Chris, Damien,
Do you still stand by your S-o-b and R-b? If so, I can push the patch in
the coming days.
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