Re: [PATCH v5] intel: New libdrm interface to create unbound wc user mappings for objects

[Martin Peres <martin.peres@linux.intel.com>]

On 09/03/16 11:09, akash.goel@intel.com wrote:
> From: Akash Goel <akash.goel@intel.com>
>
> 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@intel.com>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>

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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