+ * I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS), but on
+ * such systems we should never actually end up with a
+ * small BAR configuration, assuming we are able to load
+ * the kernel module. Hence it should be safe to treat
+ * this the same as when @probed_cpu_visible_size ==
+ * @probed_size.
+ */
+ __u64 probed_cpu_visible_size;
+
+ /**
+ * @unallocated_cpu_visible_size: Estimate of CPU
+ * visible memory remaining (-1 = unknown).
+ *
+ * Note this is only currently tracked for
+ * I915_MEMORY_CLASS_DEVICE regions, and also requires
+ * CAP_PERFMON or CAP_SYS_ADMIN to get reliable
+ * accounting. Without this the value here will always
+ * equal the @probed_cpu_visible_size.
+ */
+ __u64 unallocated_cpu_visible_size;
+ };
+ };
+};
+
+/**
+ * struct __drm_i915_gem_create_ext - Existing gem_create
behaviour, with added
+ * extension support using struct i915_user_extension.
+ *
+ * Note that new buffer flags should be added 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.
+ /**
+ * @handle: Returned handle for the object.
+ *
+ * Object handles are nonzero.
+ */
+ __u32 handle;
+ /**
+ * @flags: Optional flags.
+ *
+ * Supported values:
+ *
+ * I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS - Signal to the
kernel that
+ * the object will need to be accessed via the CPU.
+ *
+ * Only valid when placing objects in
I915_MEMORY_CLASS_DEVICE, and only
+ * strictly required on configurations where some subset of
the device
+ * memory is directly visible/mappable through the CPU(which
we also
+ * call small BAR), like on some DG2+ systems. Note that this
is quite
+ * undesirable, but due to various factors like the client
CPU, BIOS etc
+ * it's something we can expect to see in the wild. See struct
+ * __drm_i915_memory_region_info.probed_cpu_visible_size for
how to
+ * determine if this system applies.
+ *
+ * Note that one of the placements MUST be
I915_MEMORY_CLASS_SYSTEM, to
+ * ensure the kernel can always spill the allocation to system
memory,
+ * if the object can't be allocated in the mappable part of
+ * I915_MEMORY_CLASS_DEVICE.
+ *
+ * Also note that since the kernel only supports flat-CCS on
objects
+ * that can *only* be placed in I915_MEMORY_CLASS_DEVICE, we
therefore
+ * don't support I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS
together with
+ * flat-CCS.
+ *
+ * Without this hint, the kernel will assume that non-mappable
+ * I915_MEMORY_CLASS_DEVICE is preferred for this object. Note
that the
+ * kernel can still migrate the object to the mappable part,
as a last
+ * resort, if userspace ever CPU faults this object, but this
might be
+ * expensive, and so ideally should be avoided.
+ *
+ * On older kernels, where usage of this flag results in an
error, since
+ * we lack the relevant small BAR uAPI(see also struct
+ * __drm_i915_memory_region_info.probed_cpu_visible_size) it
should
+ * NEVER be possible to end up with a small BAR configuration,
assuming
+ * we can also successfully load the i915 kernel module. In
such cases
+ * the entire I915_MEMORY_CLASS_DEVICE region will be CPU
accessible,
+ * and as such there are zero restrictions on where the object
can be
+ * placed.
+ */
+#define I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS (1 << 0)
+ __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.
+ *
+ * For I915_GEM_CREATE_EXT_PROTECTED_CONTENT usage see
+ * struct drm_i915_gem_create_ext_protected_content.
+ */
+#define I915_GEM_CREATE_EXT_MEMORY_REGIONS 0
+#define I915_GEM_CREATE_EXT_PROTECTED_CONTENT 1
+ __u64 extensions;
+};
diff --git a/Documentation/gpu/rfc/i915_small_bar.rst
b/Documentation/gpu/rfc/i915_small_bar.rst
new file mode 100644
index 000000000000..a322481cea8b
--- /dev/null
+++ b/Documentation/gpu/rfc/i915_small_bar.rst
@@ -0,0 +1,47 @@
+==========================
+I915 Small BAR RFC Section
+==========================
+Starting from DG2 we will have resizable BAR support for device
local-memory(i.e
+I915_MEMORY_CLASS_DEVICE), but in some cases the final BAR size
might still be
+smaller than the total probed_size. In such cases, only some
subset of
+I915_MEMORY_CLASS_DEVICE will be CPU accessible(for example the
first 256M),
+while the remainder is only accessible via the GPU.
+
+I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS flag
+----------------------------------------------
+New gem_create_ext flag to tell the kernel that a BO will require
CPU access.
+This becomes important when placing an object in
I915_MEMORY_CLASS_DEVICE, where
+underneath the device has a small BAR, meaning only some portion
of it is CPU
+accessible. Without this flag the kernel will assume that CPU
access is not
+required, and prioritize using the non-CPU visible portion of
+I915_MEMORY_CLASS_DEVICE.
+
+.. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h
+ :functions: __drm_i915_gem_create_ext
+
+probed_cpu_visible_size attribute
+---------------------------------
+New struct__drm_i915_memory_region attribute which returns the
total size of the
+CPU accessible portion, for the particular region. This should
only be
+applicable for I915_MEMORY_CLASS_DEVICE. We also report the
+unallocated_cpu_visible_size, alongside the unallocated_size.
+
+Vulkan will need this as part of creating a separate VkMemoryHeap
with the
+VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT set, to represent the CPU
visible portion,
+where the total size of the heap needs to be known. It also wants
to be able to
+give a rough estimate of how memory can potentially be allocated.
+
+.. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h
+ :functions: __drm_i915_memory_region_info
+
+Error Capture restrictions
+--------------------------
+With error capture we have two new restrictions:
+
+ 1) Error capture is best effort on small BAR systems; if the
pages are not
+ CPU accessible, at the time of capture, then the kernel is
free to skip
+ trying to capture them.
+
+ 2) On discrete we now reject error capture on recoverable
contexts. In the
+ future the kernel may want to blit during error capture, when
for example
+ something is not currently CPU accessible.
diff --git a/Documentation/gpu/rfc/index.rst
b/Documentation/gpu/rfc/index.rst
index 91e93a705230..5a3bd3924ba6 100644
--- a/Documentation/gpu/rfc/index.rst
+++ b/Documentation/gpu/rfc/index.rst
@@ -23,3 +23,7 @@ host such documentation:
.. toctree::
i915_scheduler.rst
+
+.. toctree::
+
+ i915_small_bar.rst
