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virtio: Introduce virtio_max_dma_size()

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This function returns the maximum segment size for a single
dma transaction of a virtio device. The possible limit comes
from the SWIOTLB implementation in the Linux kernel, that
has an upper limit of (currently) 256kb of contiguous
memory it can map. Other DMA-API implementations might also
have limits.

Use the new dma_max_mapping_size() function to determine the
maximum mapping size when DMA-API is in use for virtio.

Cc: [email protected]
Reviewed-by: Konrad Rzeszutek Wilk <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Joerg Roedel <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>
This commit is contained in:
Joerg Roedel 2019-02-07 12:59:16 +01:00 • committed by Michael S. Tsirkin
commit e6d6dd6c87
2 changed files with 13 additions and 0 deletions
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11
drivers/virtio/virtio_ring.c
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@ -271,6 +271,17 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
return false;
}
size_t virtio_max_dma_size(struct virtio_device *vdev)
{
size_t max_segment_size = SIZE_MAX;
if (vring_use_dma_api(vdev))
max_segment_size = dma_max_mapping_size(&vdev->dev);
return max_segment_size;
}
EXPORT_SYMBOL_GPL(virtio_max_dma_size);
static void *vring_alloc_queue(struct virtio_device *vdev, size_t size,
dma_addr_t *dma_handle, gfp_t flag)
{