On 8/5/19 2:04 AM, Suwan Kim wrote:
On Fri, Aug 02, 2019 at 04:41:52PM -0600, shuah wrote:
Hi Suwan,
On 8/2/19 11:36 AM, Suwan Kim wrote:
There are bugs on vhci with usb 3.0 storage device.
This sentence doesn't make sense to me. What bugs? Ca you eloborate?
Alan's patch description "usb-storage: Set virt_boundary_mask to
avoid SG overflows" elaborates the problem. In USB, each SG list
entry buffer should be divisible by the bulk maxpacket size. But
with native SG support, this problem doesn't matter because the
SG buffer is treated as contiguous buffer. But without native SG
support, storage driver breaks SG list into several URBs and each
URB is sparate transfer.
Let's assume that driver request 31.5 KB data and has SG list which
has 3584 bytes buffer followed by 7 4096 bytes buffer for some
reason. USB Storage driver splits this SG list into several URBs
because VHCI doesn't support SG and send them separately. So the
first URB buffer size is 3584 bytes. When receiving data from device,
USB 3.0 device sends data packet of 1024 bytes size because the max
packet size of BULK pipe is 1024 bytes. So device sends 4096 bytes.
But the first URB buffer has only 3584 bytes buffer size. So host
controller terminates the transfer even though there is more data
to receive.
Please also reference the mail thread
https://marc.info/?t=155449209600003&r=1&w=2
https://marc.info/?l=linux-usb&m=155482317722223&w=2
I am asking you to elaborate and add it to the commit log instead of
just saying "There are bugs on vhci with usb 3.0 storage device."
thanks,
-- Shuah
