[Intel-gfx] [PATCH v3 4/4] drm/doc/rfc: i915 DG1 uAPI
Matthew Auld
matthew.auld at intel.com
Thu Apr 15 15:59:58 UTC 2021
Add an entry for the new uAPI needed for DG1.
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
Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.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
---
Documentation/gpu/rfc/i915_gem_lmem.h | 255 ++++++++++++++++++++++++
Documentation/gpu/rfc/i915_gem_lmem.rst | 139 +++++++++++++
Documentation/gpu/rfc/index.rst | 4 +
3 files changed, 398 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..2a82a452e9f2
--- /dev/null
+++ b/Documentation/gpu/rfc/i915_gem_lmem.h
@@ -0,0 +1,255 @@
+/*
+ * Note that drm_i915_query_item and drm_i915_query are existing bits of uAPI.
+ * For the regions query we are just adding a new query id, so no actual new
+ * ioctl or anything, but including it here for reference.
+ */
+struct drm_i915_query_item {
+#define DRM_I915_QUERY_MEMORY_REGIONS 0xdeadbeaf
+ ....
+ __u64 query_id;
+
+ /*
+ * When set to zero by userspace, this is filled with the size of the
+ * data to be written at the data_ptr pointer. The kernel sets this
+ * value to a negative value to signal an error on a particular query
+ * item.
+ */
+ __s32 length;
+
+ __u32 flags;
+ /*
+ * Data will be written at the location pointed by data_ptr when the
+ * value of length matches the length of the data to be written by the
+ * kernel.
+ */
+ __u64 data_ptr;
+};
+
+struct drm_i915_query {
+ __u32 num_items;
+ /*
+ * Unused for now. Must be cleared to zero.
+ */
+ __u32 flags;
+ /*
+ * This points to an array of num_items drm_i915_query_item structures.
+ */
+ __u64 items_ptr;
+};
+
+#define DRM_IOCTL_I915_QUERY DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_QUERY, struct drm_i915_query)
+
+/**
+ * enum drm_i915_gem_memory_class
+ */
+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
+ */
+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 quite a lot of 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 etc.
+ */
+struct drm_i915_memory_region_info {
+ /** @region: class:instance pair encoding */
+ struct drm_i915_gem_memory_class_instance region;
+
+ /** @rsvd0: MBZ */
+ __u32 rsvd0;
+
+ /** @caps: MBZ */
+ __u64 caps;
+
+ /** @flags: MBZ */
+ __u64 flags;
+
+ /** @probed_size: Memory probed by the driver (-1 = unknown) */
+ __u64 probed_size;
+
+ /** @unallocated_size: Estimate of memory remaining (-1 = unknown) */
+ __u64 unallocated_size;
+
+ /** @rsvd1: MBZ */
+ __u64 rsvd1[8];
+};
+
+/**
+ * struct drm_i915_query_memory_regions
+ *
+ * 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;
+
+ /** @rsvd: MBZ */
+ __u32 rsvd[3];
+
+ /** @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)
+
+/**
+ * struct drm_i915_gem_create_ext
+ *
+ * Existing gem_create behaviour, with added extension support.
+ *
+ * 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
+ * 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
+ *
+ * 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), as an array of
+ * drm_i915_gem_memory_class_instance, or an equivalent layout of class:instance
+ * pair encodings. See 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 create_ext.handle, if all went
+ * well.
+ */
+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 placements array. */
+ __u32 num_regions;
+ /**
+ * @regions: The placements array.
+ *
+ * Should be an array of 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..52f1db15ae94
--- /dev/null
+++ b/Documentation/gpu/rfc/i915_gem_lmem.rst
@@ -0,0 +1,139 @@
+=========================
+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
+* 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:
+
+Query uAPI
+----------
+Existing query interface
+^^^^^^^^^^^^^^^^^^^^^^^^
+.. kernel-doc:: include/uapi/drm/i915_drm.h
+ :functions: drm_i915_query_item drm_i915_query
+
+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
+
+It's raining extensions
+^^^^^^^^^^^^^^^^^^^^^^^
+As noted above, extensions can be supplied as a chain in gem_create_ext using the
+existing i915_user_extension. 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.
+
+.. kernel-doc:: include/uapi/drm/i915_drm.h
+ :functions: i915_user_extension
+
+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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