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@intel.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Jordan Justen jordan.l.justen@intel.com Cc: Daniel Vetter daniel.vetter@intel.com Cc: Kenneth Graunke kenneth@whitecape.org Cc: Jason Ekstrand jason@jlekstrand.net Cc: Dave Airlie airlied@gmail.com Cc: dri-devel@lists.freedesktop.org Cc: mesa-dev@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