Re: [PATCH v5 2/4] usb: xhci: Allocate sideband ring segments with dma_alloc_coherent()

[sashiko-bot@kernel.org]

> Ring segments are normally allocated from a shared DMA pool sized and
> aligned to TRB_SEGMENT_SIZE (4096 bytes). On kernels built with a
> larger PAGE_SIZE (e.g. 16K or 64K page arches), multiple segments can
> share the same physical page.
> 
> A sideband client that maps a ring buffer directly via the IOMMU
> (which operates at page granularity) would then also expose any other
> ring segment sharing that page, as well as the dma_pool bookkeeping
> kept in free blocks, to the entity handling the offloaded endpoints.
> 
> Add a no_pool_alloc flag for endpoints and rings, which has the ring
> segments allocated with dma_alloc_coherent() instead of from
> xhci->segment_pool. Coherent allocations are page aligned, so each of
> these segments gets a page of its own. When PAGE_SIZE is larger than
> TRB_SEGMENT_SIZE, xhci_sideband_add_endpoint() sets the flag for the
> [ ... ]
> the endpoint already has a ring.
> 
> Suggested-by: Mathias Nyman <mathias.nyman@linux.intel.com>
> Assisted-by: Claude:claude-opus-5-5
> Signed-off-by: Wesley Cheng <wesley.cheng@oss.qualcomm.com>

Sashiko has reviewed this patch and found no issues.

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