* Route shmem backend over to TTM SYSTEM for discrete
* TTM purgeable object support
* Move i915 buddy allocator over to TTM
- * MMAP ioctl mode(see `I915 MMAP`_)
- * SET/GET ioctl caching(see `I915 SET/GET CACHING`_)
* Send RFC(with mesa-dev on cc) for final sign off on the uAPI
* Add pciid for DG1 and turn on uAPI for real
-
-New object placement and region query uAPI
-==========================================
-Starting from DG1 we need to give userspace the ability to allocate buffers from
-device local-memory. Currently the driver supports gem_create, which can place
-buffers in system memory via shmem, and the usual assortment of other
-interfaces, like dumb buffers and userptr.
-
-To support this new capability, while also providing a uAPI which will work
-beyond just DG1, we propose to offer three new bits of uAPI:
-
-DRM_I915_QUERY_MEMORY_REGIONS
------------------------------
-New query ID which allows userspace to discover the list of supported memory
-regions(like system-memory and local-memory) for a given device. We identify
-each region with a class and instance pair, which should be unique. The class
-here would be DEVICE or SYSTEM, and the instance would be zero, on platforms
-like DG1.
-
-Side note: The class/instance design is borrowed from our existing engine uAPI,
-where we describe every physical engine in terms of its class, and the
-particular instance, since we can have more than one per class.
-
-In the future we also want to expose more information which can further
-describe the capabilities of a region.
-
-.. kernel-doc:: include/uapi/drm/i915_drm.h
- :functions: drm_i915_gem_memory_class drm_i915_gem_memory_class_instance drm_i915_memory_region_info drm_i915_query_memory_regions
-
-GEM_CREATE_EXT
---------------
-New ioctl which is basically just gem_create but now allows userspace to provide
-a chain of possible extensions. Note that if we don't provide any extensions and
-set flags=0 then we get the exact same behaviour as gem_create.
-
-Side note: We also need to support PXP[1] in the near future, which is also
-applicable to integrated platforms, and adds its own gem_create_ext extension,
-which basically lets userspace mark a buffer as "protected".
-
-.. kernel-doc:: include/uapi/drm/i915_drm.h
- :functions: drm_i915_gem_create_ext
-
-I915_GEM_CREATE_EXT_MEMORY_REGIONS
-----------------------------------
-Implemented as an extension for gem_create_ext, we would now allow userspace to
-optionally provide an immutable list of preferred placements at creation time,
-in priority order, for a given buffer object. For the placements we expect
-them each to use the class/instance encoding, as per the output of the regions
-query. Having the list in priority order will be useful in the future when
-placing an object, say during eviction.
-
-.. kernel-doc:: include/uapi/drm/i915_drm.h
- :functions: drm_i915_gem_create_ext_memory_regions
-
-One fair criticism here is that this seems a little over-engineered[2]. If we
-just consider DG1 then yes, a simple gem_create.flags or something is totally
-all that's needed to tell the kernel to allocate the buffer in local-memory or
-whatever. However looking to the future we need uAPI which can also support
-upcoming Xe HP multi-tile architecture in a sane way, where there can be
-multiple local-memory instances for a given device, and so using both class and
-instance in our uAPI to describe regions is desirable, although specifically
-for DG1 it's uninteresting, since we only have a single local-memory instance.
-
-Existing uAPI issues
-====================
-Some potential issues we still need to resolve.
-
-I915 MMAP
----------
-In i915 there are multiple ways to MMAP GEM object, including mapping the same
-object using different mapping types(WC vs WB), i.e multiple active mmaps per
-object. TTM expects one MMAP at most for the lifetime of the object. If it
-turns out that we have to backpedal here, there might be some potential
-userspace fallout.
-
-I915 SET/GET CACHING
---------------------
-In i915 we have set/get_caching ioctl. TTM doesn't let us to change this, but
-DG1 doesn't support non-snooped pcie transactions, so we can just always
-allocate as WB for smem-only buffers. If/when our hw gains support for
-non-snooped pcie transactions then we must fix this mode at allocation time as
-a new GEM extension.
-
-This is related to the mmap problem, because in general (meaning, when we're
-not running on intel cpus) the cpu mmap must not, ever, be inconsistent with
-allocation mode.
-
-Possible idea is to let the kernel picks the mmap mode for userspace from the
-following table:
-
-smem-only: WB. Userspace does not need to call clflush.
-
-smem+lmem: We only ever allow a single mode, so simply allocate this as uncached
-memory, and always give userspace a WC mapping. GPU still does snooped access
-here(assuming we can't turn it off like on DG1), which is a bit inefficient.
-
-lmem only: always WC
-
-This means on discrete you only get a single mmap mode, all others must be
-rejected. That's probably going to be a new default mode or something like
-that.
-
-Links
-=====
-[1] https://patchwork.freedesktop.org/series/86798/
-
-[2] https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5599#note_553791
projects / platform / kernel / linux-rpi.git / commitdiff