From 48df4a6fd8c40c0bbcbca2044f5f2bc75dcf6db1 Mon Sep 17 00:00:00 2001 From: Sarah Sharp Date: Fri, 12 Aug 2011 10:23:01 -0700 Subject: xhci: Handle zero-length isochronous packets. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit For a long time, the xHCI driver has had this note: /* FIXME: Ignoring zero-length packets, can those happen? */ It turns out that, yes, there are drivers that need to queue zero-length transfers for isochronous OUT transfers. Without this patch, users will see kernel hang messages when a driver attempts to enqueue an isochronous URB with a zero length transfer (because count_isoc_trbs_needed will return zero for that TD, xhci_td->last_trb will never be set, and updating the dequeue pointer will cause an infinite loop). Matěj ran into this issue when using an NI Audio4DJ USB soundcard with the snd-usb-caiaq driver. See https://bugzilla.kernel.org/show_bug.cgi?id=40702 Fix count_isoc_trbs_needed() to return 1 for zero-length transfers (thanks Alan on the math help). Update the various TRB field calculations to deal with zero-length transfers. We're still transferring one packet with a zero-length data payload, so the total_packet_count should be 1. The Transfer Burst Count (TBC) and Transfer Last Burst Packet Count (TLBPC) fields should be set to zero. This patch should be backported to kernels as old as 2.6.36. Signed-off-by: Sarah Sharp Tested-by: Matěj Laitl Cc: Daniel Mack Cc: Alan Stern Cc: stable@kernel.org --- drivers/usb/host/xhci-ring.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-) (limited to 'drivers/usb') diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c index b2d654b7477..54139a2f06c 100644 --- a/drivers/usb/host/xhci-ring.c +++ b/drivers/usb/host/xhci-ring.c @@ -2684,6 +2684,10 @@ static u32 xhci_v1_0_td_remainder(int running_total, int trb_buff_len, { int packets_transferred; + /* One TRB with a zero-length data packet. */ + if (running_total == 0 && trb_buff_len == 0) + return 0; + /* All the TRB queueing functions don't count the current TRB in * running_total. */ @@ -3125,20 +3129,15 @@ static int count_isoc_trbs_needed(struct xhci_hcd *xhci, struct urb *urb, int i) { int num_trbs = 0; - u64 addr, td_len, running_total; + u64 addr, td_len; addr = (u64) (urb->transfer_dma + urb->iso_frame_desc[i].offset); td_len = urb->iso_frame_desc[i].length; - running_total = TRB_MAX_BUFF_SIZE - (addr & (TRB_MAX_BUFF_SIZE - 1)); - running_total &= TRB_MAX_BUFF_SIZE - 1; - if (running_total != 0) - num_trbs++; - - while (running_total < td_len) { + num_trbs = DIV_ROUND_UP(td_len + (addr & (TRB_MAX_BUFF_SIZE - 1)), + TRB_MAX_BUFF_SIZE); + if (num_trbs == 0) num_trbs++; - running_total += TRB_MAX_BUFF_SIZE; - } return num_trbs; } @@ -3250,9 +3249,11 @@ static int xhci_queue_isoc_tx(struct xhci_hcd *xhci, gfp_t mem_flags, addr = start_addr + urb->iso_frame_desc[i].offset; td_len = urb->iso_frame_desc[i].length; td_remain_len = td_len; - /* FIXME: Ignoring zero-length packets, can those happen? */ total_packet_count = roundup(td_len, le16_to_cpu(urb->ep->desc.wMaxPacketSize)); + /* A zero-length transfer still involves at least one packet. */ + if (total_packet_count == 0) + total_packet_count++; burst_count = xhci_get_burst_count(xhci, urb->dev, urb, total_packet_count); residue = xhci_get_last_burst_packet_count(xhci, -- cgit v1.2.3