> From: linux-usb-owner@xxxxxxxxxxxxxxx [mailto:linux-usb-owner@xxxxxxxxxxxxxxx] On Behalf Of David Laight > Sent: Friday, October 03, 2014 6:08 AM > > From: Mathias Nyman > > On 10/01/2014 05:50 PM, vichy wrote: > > > hi Mathias: > > > > > >> > > >> In xhci-ring.c, static int xhci_queue_isoc_tx(): > > >> > > >> /* Calculate TRB length */ > > >> trb_buff_len = TRB_MAX_BUFF_SIZE - (addr & ((1 << TRB_MAX_BUFF_SHIFT) - 1)); > > >> > > >> where addr = start_addr + urb->iso_frame_desc[i].offset; > > >> > > >> this limits the trb_buff_len to stop the trb buffer at TRB_MAX_BUFF_SIZE boundary > > > Yes, you are right. > > > the above is make sure trb buffer will not cross over > > > TRB_MAX_BUFF_SIZE boundary. > > > But it still possible to cross the page boundary for ISO trb, right? > > > (suppose page boundary is 4KB, TRB_MAX_BUFF_SIZE is 64KB) > > > > > > appreciate your kind help, > > > > > > > Hi > > > > As I understood it, it is ok to cross page boundaries as long as the buffer is physically contiguous. > > As our dma case should be. > > xhci specification section 3.2.8 says that: > > > > "Note that no constraints are placed on the TRB Length fields in a Scatter/Gather list. Classically > > all the > > buffers pointed to by a scatter gather list were required to be “page size” in length except for the > > first and > > last (as illustrated by the example above). The xHCI does not require this constraint. Any buffer > > pointed to > > by a Normal, Data Stage, or Isoch TRB in a TD may be any size between 0 and 64K bytes in size. For > > instance, if when an OS translates a virtual memory buffer into a list of physical pages, some of the > > entries > > in the list reference multiple contiguous pages, the flexible Length fields of TRBs allow a 1:1 > > mapping of list > > entries to TRBs, i.e. a multi-page list entry does not need to be defined as multiple page sized > > TRBs." > > " > > The ohci hardware requires that scatter-gather boundaries occur on USB message boundaries. > > The xhi hardware doesn't have that constraint, but has the different constraints: > 1) A buffer must not cross a 64k address boundary. > 2) A LINK TRB (at the end of the ring) must only occur at a USB message boundary > (actually it is a slightly tighter constraint). > In combination those two are a PITA. Hi David, May I ask where in the xHCI spec is 2) stated? I'm not finding it (looking at "Revision 1.0 with errata to 7/12/12"). I can't find "message boundary" anywhere in the spec. Did you mean packet boundary? If so, there is some text in the spec which contradicts that. In 4.11.7.1, it says: "In Figure 26 the IOC flag only may be set in TRBs 5 and 10 ... Note that THE LINK TRB DOES NOT LAND ON A PACKET BOUNDARY relative to the start of TD Fragment 1, so its IOC flag may not be set." (emphasis mine) -- Paul ��.n��������+%������w��{.n�����{���)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
