Hi Suwan,
On 8/2/19 11:36 AM, Suwan Kim wrote:
There are bugs on vhci with usb 3.0 storage device. Currently, vhci
doesn't supported SG, so USB storage driver on vhci breaks SG list
into multiple URBs and it causes error that a transfer got terminated
too early because the transfer length for one of the URBs was not
divisible by the maxpacket size.
In this patch, vhci supports SG regardless of whether the server's
host controller supports SG or not, because stub driver splits SG
list into several URBs if the server's host controller doesn't
support SG.
To support SG, vhci_map_urb_for_dma() sets URB_DMA_MAP_SG flag in
urb->transfer_flags if URB has SG list and this flag will tell stub
driver to use SG list.
vhci sends each SG list entry to stub driver. Then, stub driver sees
the total length of the buffer and allocates SG table and pages
according to the total buffer length calling sgl_alloc(). After stub
driver receives completed URB, it again sends each SG list entry to
vhci.
If the server's host controller doesn't support SG, stub driver
breaks a single SG request into several URBs and submits them to
the server's host controller. When all the split URBs are completed,
stub driver reassembles the URBs into a single return command and
sends it to vhci.
Alan fixed vhci bug with the USB 3.0 storage device by modifying
USB storage driver.
("usb-storage: Set virt_boundary_mask to avoid SG overflows")
But the fundamental solution of it is to add SG support to vhci.
This patch works well with the USB 3.0 storage devices without Alan's
patch, and we can revert Alan's patch if it causes some troubles.
Why just 3.0? Please test with lowspeed and VUDC to make sure there are
no regressions.
thanks,
-- Shuah
