diff options
Diffstat (limited to 'drivers/usb/core/usb.c')
| -rw-r--r-- | drivers/usb/core/usb.c | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c index c611b3cbc67..0fee5c66fd6 100644 --- a/drivers/usb/core/usb.c +++ b/drivers/usb/core/usb.c @@ -579,11 +579,12 @@ int __usb_get_extra_descriptor(char *buffer, unsigned size, * address (through the pointer provided). * * These buffers are used with URB_NO_xxx_DMA_MAP set in urb->transfer_flags - * to avoid behaviors like using "DMA bounce buffers", or tying down I/O - * mapping hardware for long idle periods. The implementation varies between + * to avoid behaviors like using "DMA bounce buffers", or thrashing IOMMU + * hardware during URB completion/resubmit. The implementation varies between * platforms, depending on details of how DMA will work to this device. - * Using these buffers also helps prevent cacheline sharing problems on - * architectures where CPU caches are not DMA-coherent. + * Using these buffers also eliminates cacheline sharing problems on + * architectures where CPU caches are not DMA-coherent. On systems without + * bus-snooping caches, these buffers are uncached. * * When the buffer is no longer used, free it with usb_buffer_free(). */ @@ -608,7 +609,7 @@ void *usb_buffer_alloc( * * This reclaims an I/O buffer, letting it be reused. The memory must have * been allocated using usb_buffer_alloc(), and the parameters must match - * those provided in that allocation request. + * those provided in that allocation request. */ void usb_buffer_free( struct usb_device *dev, |