[PATCH 1/9] drm/doc/rfc: i915 DG1 uAPI
Jason Ekstrand
jason at jlekstrand.net
Mon Apr 26 16:25:09 UTC 2021
On Mon, Apr 26, 2021 at 10:31 AM Matthew Auld <matthew.auld at intel.com> wrote:
>
> On 26/04/2021 16:11, Jason Ekstrand wrote:
> > On Mon, Apr 26, 2021 at 4:42 AM Matthew Auld <matthew.auld at intel.com> wrote:
> >>
> >> Add an entry for the new uAPI needed for DG1. Also add the overall
> >> upstream plan, including some notes for the TTM conversion.
> >>
> >> v2(Daniel):
> >> - include the overall upstreaming plan
> >> - add a note for mmap, there are differences here for TTM vs i915
> >> - bunch of other suggestions from Daniel
> >> v3:
> >> (Daniel)
> >> - add a note for set/get caching stuff
> >> - add some more docs for existing query and extensions stuff
> >> - add an actual code example for regions query
> >> - bunch of other stuff
> >> (Jason)
> >> - uAPI change(!):
> >> - try a simpler design with the placements extension
> >> - rather than have a generic setparam which can cover multiple
> >> use cases, have each extension be responsible for one thing
> >> only
> >> v4:
> >> (Daniel)
> >> - add some more notes for ttm conversion
> >> - bunch of other stuff
> >> (Jason)
> >> - uAPI change(!):
> >> - drop all the extra rsvd members for the region_query and
> >> region_info, just keep the bare minimum needed for padding
> >>
> >> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> >> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> >> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> >> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> >> Cc: Lionel Landwerlin <lionel.g.landwerlin at linux.intel.com>
> >> Cc: Jon Bloomfield <jon.bloomfield at intel.com>
> >> Cc: Jordan Justen <jordan.l.justen at intel.com>
> >> Cc: Daniel Vetter <daniel.vetter at intel.com>
> >> Cc: Kenneth Graunke <kenneth at whitecape.org>
> >> Cc: Jason Ekstrand <jason at jlekstrand.net>
> >> Cc: Dave Airlie <airlied at gmail.com>
> >> Cc: dri-devel at lists.freedesktop.org
> >> Cc: mesa-dev at lists.freedesktop.org
> >> Acked-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> >> Acked-by: Dave Airlie <airlied at redhat.com>
> >> ---
> >> Documentation/gpu/rfc/i915_gem_lmem.h | 212 ++++++++++++++++++++++++
> >> Documentation/gpu/rfc/i915_gem_lmem.rst | 130 +++++++++++++++
> >> Documentation/gpu/rfc/index.rst | 4 +
> >> 3 files changed, 346 insertions(+)
> >> create mode 100644 Documentation/gpu/rfc/i915_gem_lmem.h
> >> create mode 100644 Documentation/gpu/rfc/i915_gem_lmem.rst
> >>
> >> diff --git a/Documentation/gpu/rfc/i915_gem_lmem.h b/Documentation/gpu/rfc/i915_gem_lmem.h
> >> new file mode 100644
> >> index 000000000000..7ed59b6202d5
> >> --- /dev/null
> >> +++ b/Documentation/gpu/rfc/i915_gem_lmem.h
> >> @@ -0,0 +1,212 @@
> >> +/**
> >> + * enum drm_i915_gem_memory_class - Supported memory classes
> >> + */
> >> +enum drm_i915_gem_memory_class {
> >> + /** @I915_MEMORY_CLASS_SYSTEM: System memory */
> >> + I915_MEMORY_CLASS_SYSTEM = 0,
> >> + /** @I915_MEMORY_CLASS_DEVICE: Device local-memory */
> >> + I915_MEMORY_CLASS_DEVICE,
> >> +};
> >> +
> >> +/**
> >> + * struct drm_i915_gem_memory_class_instance - Identify particular memory region
> >> + */
> >> +struct drm_i915_gem_memory_class_instance {
> >> + /** @memory_class: See enum drm_i915_gem_memory_class */
> >> + __u16 memory_class;
> >> +
> >> + /** @memory_instance: Which instance */
> >> + __u16 memory_instance;
> >> +};
> >> +
> >> +/**
> >> + * struct drm_i915_memory_region_info - Describes one region as known to the
> >> + * driver.
> >> + *
> >> + * Note that we reserve some stuff here for potential future work. As an example
> >> + * we might want expose the capabilities(see @caps) for a given region, which
> >> + * could include things like if the region is CPU mappable/accessible, what are
> >> + * the supported mapping types etc.
> >> + *
> >> + * Note this is using both struct drm_i915_query_item and struct drm_i915_query.
> >> + * For this new query we are adding the new query id DRM_I915_QUERY_MEMORY_REGIONS
> >> + * at &drm_i915_query_item.query_id.
> >> + */
> >> +struct drm_i915_memory_region_info {
> >> + /** @region: The class:instance pair encoding */
> >> + struct drm_i915_gem_memory_class_instance region;
> >> +
> >> + /** @pad: MBZ */
> >> + __u32 pad;
> >> +
> >> + /** @caps: MBZ */
> >> + __u64 caps;
> >> +
> >> + /** @probed_size: Memory probed by the driver (-1 = unknown) */
> >> + __u64 probed_size;
> >> +
> >> + /** @unallocated_size: Estimate of memory remaining (-1 = unknown) */
> >> + __u64 unallocated_size;
> >> +};
> >> +
> >> +/**
> >> + * struct drm_i915_query_memory_regions
> >> + *
> >> + * The region info query enumerates all regions known to the driver by filling
> >> + * in an array of struct drm_i915_memory_region_info structures.
> >> + *
> >> + * Example for getting the list of supported regions:
> >> + *
> >> + * .. code-block:: C
> >> + *
> >> + * struct drm_i915_query_memory_regions *info;
> >> + * struct drm_i915_query_item item = {
> >> + * .query_id = DRM_I915_QUERY_MEMORY_REGIONS;
> >> + * };
> >> + * struct drm_i915_query query = {
> >> + * .num_items = 1,
> >> + * .items_ptr = (uintptr_t)&item,
> >> + * };
> >> + * int err, i;
> >> + *
> >> + * // First query the size of the blob we need, this needs to be large
> >> + * // enough to hold our array of regions. The kernel will fill out the
> >> + * // item.length for us, which is the number of bytes we need.
> >> + * err = ioctl(fd, DRM_IOCTL_I915_QUERY, &query);
> >> + * if (err) ...
> >> + *
> >> + * info = calloc(1, item.length);
> >> + * // Now that we allocated the required number of bytes, we call the ioctl
> >> + * // again, this time with the data_ptr pointing to our newly allocated
> >> + * // blob, which the kernel can then populate with the all the region info.
> >> + * item.data_ptr = (uintptr_t)&info,
> >> + *
> >> + * err = ioctl(fd, DRM_IOCTL_I915_QUERY, &query);
> >> + * if (err) ...
> >> + *
> >> + * // We can now access each region in the array
> >> + * for (i = 0; i < info->num_regions; i++) {
> >> + * struct drm_i915_memory_region_info mr = info->regions[i];
> >> + * u16 class = mr.region.class;
> >> + * u16 instance = mr.region.instance;
> >> + *
> >> + * ....
> >> + * }
> >> + *
> >> + * free(info);
> >> + */
> >> +struct drm_i915_query_memory_regions {
> >> + /** @num_regions: Number of supported regions */
> >> + __u32 num_regions;
> >> +
> >> + /** @pad: MBZ */
> >> + __u32 pad;
> >> +
> >> + /** @regions: Info about each supported region */
> >> + struct drm_i915_memory_region_info regions[];
> >> +};
> >> +
> >> +#define DRM_I915_GEM_CREATE_EXT 0xdeadbeaf
> >> +#define DRM_IOCTL_I915_GEM_CREATE_EXT DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_CREATE_EXT, struct drm_i915_gem_create_ext)
> >
> > Here's another thought: Instead of burning a new IOCTL number, should
> > we just re-use DRM_I915_GEM_CREATE? The different structure size
> > should let us tell the two apart.
>
> Yeah, it was exactly like that in the original version[1]. Scrolling
> through the review comments, I think the concern was with an older
> kernel just silently ignoring the extensions with new userspace.
>
> [1] https://patchwork.freedesktop.org/patch/404455/?series=84344&rev=1
Yeah, I think Chris is right. I just dug through the code and there
really is no way for us to reject different sized structs; they just
show up zero-extended. That's aggravating.
--Jason
> >
> > --Jason
> >
> >
> >> +
> >> +/**
> >> + * struct drm_i915_gem_create_ext - Existing gem_create behaviour, with added
> >> + * extension support using struct i915_user_extension.
> >> + *
> >> + * Note that in the future we want to have our buffer flags here, at least for
> >> + * the stuff that is immutable. Previously we would have two ioctls, one to
> >> + * create the object with gem_create, and another to apply various parameters,
> >> + * however this creates some ambiguity for the params which are considered
> >> + * immutable. Also in general we're phasing out the various SET/GET ioctls.
> >> + */
> >> +struct drm_i915_gem_create_ext {
> >> + /**
> >> + * @size: Requested size for the object.
> >> + *
> >> + * The (page-aligned) allocated size for the object will be returned.
> >> + *
> >> + * Note that for some devices we have might have further minimum
> >> + * page-size restrictions(larger than 4K), like for device local-memory.
> >> + * However in general the final size here should always reflect any
> >> + * rounding up, if for example using the I915_GEM_CREATE_EXT_MEMORY_REGIONS
> >> + * extension to place the object in device local-memory.
> >> + */
> >> + __u64 size;
> >> + /**
> >> + * @handle: Returned handle for the object.
> >> + *
> >> + * Object handles are nonzero.
> >> + */
> >> + __u32 handle;
> >> + /** @flags: MBZ */
> >> + __u32 flags;
> >> + /**
> >> + * @extensions: The chain of extensions to apply to this object.
> >> + *
> >> + * This will be useful in the future when we need to support several
> >> + * different extensions, and we need to apply more than one when
> >> + * creating the object. See struct i915_user_extension.
> >> + *
> >> + * If we don't supply any extensions then we get the same old gem_create
> >> + * behaviour.
> >> + *
> >> + * For I915_GEM_CREATE_EXT_MEMORY_REGIONS usage see
> >> + * struct drm_i915_gem_create_ext_memory_regions.
> >> + */
> >> +#define I915_GEM_CREATE_EXT_MEMORY_REGIONS 0
> >> + __u64 extensions;
> >> +};
> >> +
> >> +/**
> >> + * struct drm_i915_gem_create_ext_memory_regions - The
> >> + * I915_GEM_CREATE_EXT_MEMORY_REGIONS extension.
> >> + *
> >> + * Set the object with the desired set of placements/regions in priority
> >> + * order. Each entry must be unique and supported by the device.
> >> + *
> >> + * This is provided as an array of struct drm_i915_gem_memory_class_instance, or
> >> + * an equivalent layout of class:instance pair encodings. See struct
> >> + * drm_i915_query_memory_regions and DRM_I915_QUERY_MEMORY_REGIONS for how to
> >> + * query the supported regions for a device.
> >> + *
> >> + * As an example, on discrete devices, if we wish to set the placement as
> >> + * device local-memory we can do something like:
> >> + *
> >> + * .. code-block:: C
> >> + *
> >> + * struct drm_i915_gem_memory_class_instance region_lmem = {
> >> + * .memory_class = I915_MEMORY_CLASS_DEVICE,
> >> + * .memory_instance = 0,
> >> + * };
> >> + * struct drm_i915_gem_create_ext_memory_regions regions = {
> >> + * .base = { .name = I915_GEM_CREATE_EXT_MEMORY_REGIONS },
> >> + * .regions = (uintptr_t)®ion_lmem,
> >> + * .num_regions = 1,
> >> + * };
> >> + * struct drm_i915_gem_create_ext create_ext = {
> >> + * .size = 16 * PAGE_SIZE,
> >> + * .extensions = (uintptr_t)®ions,
> >> + * };
> >> + *
> >> + * int err = ioctl(fd, DRM_IOCTL_I915_GEM_CREATE_EXT, &create_ext);
> >> + * if (err) ...
> >> + *
> >> + * At which point we get the object handle in &drm_i915_gem_create_ext.handle,
> >> + * along with the final object size in &drm_i915_gem_create_ext.size, which
> >> + * should account for any rounding up, if required.
> >> + */
> >> +struct drm_i915_gem_create_ext_memory_regions {
> >> + /** @base: Extension link. See struct i915_user_extension. */
> >> + struct i915_user_extension base;
> >> +
> >> + /** @pad: MBZ */
> >> + __u32 pad;
> >> + /** @num_regions: Number of elements in the @regions array. */
> >> + __u32 num_regions;
> >> + /**
> >> + * @regions: The regions/placements array.
> >> + *
> >> + * An array of struct drm_i915_gem_memory_class_instance.
> >> + */
> >> + __u64 regions;
> >> +};
> >> diff --git a/Documentation/gpu/rfc/i915_gem_lmem.rst b/Documentation/gpu/rfc/i915_gem_lmem.rst
> >> new file mode 100644
> >> index 000000000000..462f1efd9003
> >> --- /dev/null
> >> +++ b/Documentation/gpu/rfc/i915_gem_lmem.rst
> >> @@ -0,0 +1,130 @@
> >> +=========================
> >> +I915 DG1/LMEM RFC Section
> >> +=========================
> >> +
> >> +Upstream plan
> >> +=============
> >> +For upstream the overall plan for landing all the DG1 stuff and turning it for
> >> +real, with all the uAPI bits is:
> >> +
> >> +* Merge basic HW enabling of DG1(still without pciid)
> >> +* Merge the uAPI bits behind special CONFIG_BROKEN(or so) flag
> >> + * At this point we can still make changes, but importantly this lets us
> >> + start running IGTs which can utilize local-memory in CI
> >> +* Convert over to TTM, make sure it all keeps working. Some of the work items:
> >> + * TTM shrinker for discrete
> >> + * dma_resv_lockitem for full dma_resv_lock, i.e not just trylock
> >> + * Use TTM CPU pagefault handler
> >> + * 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`_)
> >> +* 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:: Documentation/gpu/rfc/i915_gem_lmem.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 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:: Documentation/gpu/rfc/i915_gem_lmem.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:: Documentation/gpu/rfc/i915_gem_lmem.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 allocate uncached memory, and give userspace a WC mapping
> >> +for when the buffer is in smem, and WC when it's in lmem. GPU does snooped
> >> +access, 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
> >> diff --git a/Documentation/gpu/rfc/index.rst b/Documentation/gpu/rfc/index.rst
> >> index a8621f7dab8b..05670442ca1b 100644
> >> --- a/Documentation/gpu/rfc/index.rst
> >> +++ b/Documentation/gpu/rfc/index.rst
> >> @@ -15,3 +15,7 @@ host such documentation:
> >>
> >> * Once the code has landed move all the documentation to the right places in
> >> the main core, helper or driver sections.
> >> +
> >> +.. toctree::
> >> +
> >> + i915_gem_lmem.rst
> >> --
> >> 2.26.3
> >>
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