1 ========================== 2 I915 Small BAR RFC Section 3 ========================== 4 Starting from DG2 we will have resizable BAR support for device local-memory(i.e 5 I915_MEMORY_CLASS_DEVICE), but in some cases the final BAR size might still be 6 smaller than the total probed_size. In such cases, only some subset of 7 I915_MEMORY_CLASS_DEVICE will be CPU accessible(for example the first 256M), 8 while the remainder is only accessible via the GPU. 9 10 I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS flag 11 ---------------------------------------------- 12 New gem_create_ext flag to tell the kernel that a BO will require CPU access. 13 This becomes important when placing an object in I915_MEMORY_CLASS_DEVICE, where 14 underneath the device has a small BAR, meaning only some portion of it is CPU 15 accessible. Without this flag the kernel will assume that CPU access is not 16 required, and prioritize using the non-CPU visible portion of 17 I915_MEMORY_CLASS_DEVICE. 18 19 .. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h 20 :functions: __drm_i915_gem_create_ext 21 22 probed_cpu_visible_size attribute 23 --------------------------------- 24 New struct__drm_i915_memory_region attribute which returns the total size of the 25 CPU accessible portion, for the particular region. This should only be 26 applicable for I915_MEMORY_CLASS_DEVICE. We also report the 27 unallocated_cpu_visible_size, alongside the unallocated_size. 28 29 Vulkan will need this as part of creating a separate VkMemoryHeap with the 30 VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT set, to represent the CPU visible portion, 31 where the total size of the heap needs to be known. It also wants to be able to 32 give a rough estimate of how memory can potentially be allocated. 33 34 .. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h 35 :functions: __drm_i915_memory_region_info 36 37 Error Capture restrictions 38 -------------------------- 39 With error capture we have two new restrictions: 40 41 1) Error capture is best effort on small BAR systems; if the pages are not 42 CPU accessible, at the time of capture, then the kernel is free to skip 43 trying to capture them. 44 45 2) On discrete and newer integrated platforms we now reject error capture 46 on recoverable contexts. In the future the kernel may want to blit during 47 error capture, when for example something is not currently CPU accessible.
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