Re: [PATCH v4] drm/xe: Convert stolen memory over to ttm_range_manager

[Matthew Auld <matthew.auld@intel.com>]

On 22/04/2026 13:55, Sanjay Yadav wrote:
> Stolen memory requires physically contiguous allocations for display
> scanout and compressed framebuffers. The stolen memory manager was
> sharing the gpu_buddy allocator backend with the VRAM manager, but
> buddy manages non-contiguous power-of-two blocks making it a poor fit.
> Stolen memory also has fundamentally different allocation patterns:
> 
> - Allocation sizes are not power-of-two. Since buddy rounds up to the
>    next power-of-two block size, a ~17MB request can fail even with
>    ~22MB free, because the free space is fragmented across non-fitting
>    power-of-two blocks.
> - Hardware restrictions prevent using the first 4K page of stolen for
>    certain allocations (e.g., FBC). The display code sets fpfn=1 to
>    enforce this, but when fpfn != 0, gpu_buddy enables
>    GPU_BUDDY_RANGE_ALLOCATION mode which disables the try_harder
>    coalescing path, further reducing allocation success.
> 
> This combination caused FBC compressed framebuffer (CFB) allocation
> failures on platforms like NVL/PTL. In case of NVL where stolen memory
> is ~56MB and the initial plane framebuffer consumes ~34MB at probe time,
> leaving ~22MB for subsequent allocations.
> 
> Use ttm_range_man_init_nocheck() to set up a drm_mm-backed TTM resource
> manager for stolen memory. This reuses the TTM core's ttm_range_manager
> callbacks, avoiding duplicate implementations.
> 
> Tested on NVL with a 4K DP display: stolen_mm shows a single ~22MB
> contiguous free hole after initial plane framebuffer allocation, and
> FBC successfully allocates its CFB from that region. The corresponding
> IGT was previously skipped and now passes.
> 
> v2:
> - Clarify that stolen memory requires contiguous allocations (Matt B)
> - Properly handle xe_ttm_resource_visible() for stolen instead of
>    unconditionally returning true (Matt A)
> 
> v3:
> - Rebase
> - Fix xe_display_bo_fbdev_prefer_stolen() to compare in pages, since
>    ttm_range_manager stores stolen->size in pages not bytes (Matt A)
> 
> v4:
> - Add kernel-doc for struct xe_ttm_stolen_mgr (Matt B)
> 
> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/7631
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Suggested-by: Matthew Auld <matthew.auld@intel.com>
> Assisted-by: GitHub Copilot:claude-sonnet-4.6
> Signed-off-by: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
> Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Acked-by: Vinod Govindapillai <vinod.govindapillai@intel.com>

Reviewed-by: Matthew Auld <matthew.auld@intel.com>