Am Montag, den 04.11.2019, 22:44 +0100 schrieb Greg Kroah-Hartman:
From: Alan Stern stern@rowland.harvard.edu
commit 1186f86a71130a7635a20843e355bb880c7349b2 upstream.
Commit 3ae62a42090f ("UAS: fix alignment of scatter/gather segments"), copying a similar commit for usb-storage, attempted to solve a problem involving scatter-gather I/O and USB/IP by setting the virt_boundary_mask for mass-storage devices.
We have that in 4.4.x
However, it now turns out that the analogous change in usb-storage interacted badly with commit 09324d32d2a0 ("block: force an unlimited segment size on queues with a virt boundary"), which was added later. A typical error message is:
09324d32d2a0 I cannot find.
ehci-pci 0000:00:13.2: swiotlb buffer is full (sz: 327680 bytes), total 32768 (slots), used 97 (slots)
There is no longer any reason to keep the virt_boundary_mask setting in the uas driver. It was needed in the first place only for handling devices with a block size smaller than the maxpacket size and where the host controller was not capable of fully general scatter-gather operation (that is, able to merge two SG segments into a single USB packet). But:
High-speed or slower connections never use a bulk maxpacket value larger than 512;
The SCSI layer does not handle block devices with a block size smaller than 512 bytes;
All the host controllers capable of SuperSpeed operation can handle fully general SG;
Since commit ea44d190764b ("usbip: Implement SG support to vhci-hcd and stub driver") was merged, the USB/IP driver can also handle SG.
Neither can I find ea44d190764b.
It seems to me that, while the patch is necessary in upstream, in 4.4.x it would break usbip.
Regards Oliver