From 32eaeae177bf77fbc224c35262add45bd5e6abb3 Mon Sep 17 00:00:00 2001 From: Clemens Ladisch Date: Sat, 15 Oct 2011 18:14:39 +0200 Subject: [PATCH] firewire: ohci: work around selfID junk due to wrong gap count If a device's firmware initiates a bus reset by setting the IBR bit in PHY register 1 without resetting the gap count field to 63 (and without having sent a PHY configuration packet beforehand), the gap count of this node will remain at the old value after the bus reset and thus be inconsistent with the gap count on all other nodes. The bus manager is supposed to detect the inconsistent gap count values in the self ID packets and correct them by issuing another bus reset. However, if the buggy device happens to be the cycle master, and if it sends a cycle start packet immediately after the bus reset (which is likely after a long bus reset), then the time between the end of the selfID phase and the start of the cycle start packet will be based on the too-small gap count value, so this gap will be too short to be detected as a subaction gap by the other nodes. This means that the cycle start packet will be assumed to be self ID data, and will be stored after the actual self ID quadlets in the self ID buffer. This garbage in the self ID buffer made firewire-core ignore all of the self ID data, and thus prevented the Linux bus manager from correcting the problem. Furthermore, because the bus reset handling was aborted completely, asynchronous transfers would be no longer handled correctly, and fw_run_transaction() would hang until the next bus reset. To fix this, make the detection of inconsistent self IDs more discriminating: If the invalid data in the self ID buffer looks like a cycle start packet, we can assume that the previous data in the buffer is correctly received self ID information, and process it normally. (We inspect only the first quadlet of the cycle start packet, because this value is different enough from any valid self ID quadlet, and many controllers do not store the cycle start packet in five quadlets because they expect self ID data to have an even number of quadlets.) This bug has been observed when a bus-powered DesktopKonnekt6 is switched off with its power button. Signed-off-by: Clemens Ladisch Signed-off-by: Stefan Richter --- drivers/firewire/ohci.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c index bffc2ad7ecab..b6977149394e 100644 --- a/drivers/firewire/ohci.c +++ b/drivers/firewire/ohci.c @@ -1860,8 +1860,22 @@ static void bus_reset_work(struct work_struct *work) for (i = 1, j = 0; j < self_id_count; i += 2, j++) { if (ohci->self_id_cpu[i] != ~ohci->self_id_cpu[i + 1]) { - fw_notify("inconsistent self IDs\n"); - return; + /* + * If the invalid data looks like a cycle start packet, + * it's likely to be the result of the cycle master + * having a wrong gap count. In this case, the self IDs + * so far are valid and should be processed so that the + * bus manager can then correct the gap count. + */ + if (cond_le32_to_cpu(ohci->self_id_cpu[i]) + == 0xffff008f) { + fw_notify("ignoring spurious self IDs\n"); + self_id_count = j; + break; + } else { + fw_notify("inconsistent self IDs\n"); + return; + } } ohci->self_id_buffer[j] = cond_le32_to_cpu(ohci->self_id_cpu[i]); -- 2.30.2