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diff --git a/Documentation/gpu/rfc/i915_small_bar.rst b/Documentation/gpu/rfc/i915_small_bar.rst new file mode 100644 index 000000000..d6c03ce3b --- /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 and newer integrated platforms 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. |