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authorStefan Richter <stefanr@s5r6.in-berlin.de>2015-11-03 01:46:21 +0100
committerStefan Richter <stefanr@s5r6.in-berlin.de>2015-11-05 14:17:30 +0100
commit100ceb66d5c40cc0c7018e06a9474302470be73c (patch)
treeaa4c84eff121d18f097c419616aa03864e28c6a0 /drivers/firewire
parent6a13feb9c82803e2b815eca72fa7a9f5561d7861 (diff)
firewire: ohci: fix JMicron JMB38x IT context discovery
Reported by Clifford and Craig for JMicron OHCI-1394 + SDHCI combo controllers: Often or even most of the time, the controller is initialized with the message "added OHCI v1.10 device as card 0, 4 IR + 0 IT contexts, quirks 0x10". With 0 isochronous transmit DMA contexts (IT contexts), applications like audio output are impossible. However, OHCI-1394 demands that at least 4 IT contexts are implemented by the link layer controller, and indeed JMicron JMB38x do implement four of them. Only their IsoXmitIntMask register is unreliable at early access. With my own JMB381 single function controller I found: - I can reproduce the problem with a lower probability than Craig's. - If I put a loop around the section which clears and reads IsoXmitIntMask, then either the first or the second attempt will return the correct initial mask of 0x0000000f. I never encountered a case of needing more than a second attempt. - Consequently, if I put a dummy reg_read(...IsoXmitIntMaskSet) before the first write, the subsequent read will return the correct result. - If I merely ignore a wrong read result and force the known real result, later isochronous transmit DMA usage works just fine. So let's just fix this chip bug up by the latter method. Tested with JMB381 on kernel 3.13 and 4.3. Since OHCI-1394 generally requires 4 IT contexts at a minium, this workaround is simply applied whenever the initial read of IsoXmitIntMask returns 0, regardless whether it's a JMicron chip or not. I never heard of this issue together with any other chip though. I am not 100% sure that this fix works on the OHCI-1394 part of JMB380 and JMB388 combo controllers exactly the same as on the JMB381 single- function controller, but so far I haven't had a chance to let an owner of a combo chip run a patched kernel. Strangely enough, IsoRecvIntMask is always reported correctly, even though it is probed right before IsoXmitIntMask. Reported-by: Clifford Dunn Reported-by: Craig Moore <craig.moore@qenos.com> Cc: stable@vger.kernel.org Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Diffstat (limited to 'drivers/firewire')
-rw-r--r--drivers/firewire/ohci.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c
index f51d376d10ba..c2f5117fd8cb 100644
--- a/drivers/firewire/ohci.c
+++ b/drivers/firewire/ohci.c
@@ -3675,6 +3675,11 @@ static int pci_probe(struct pci_dev *dev,
reg_write(ohci, OHCI1394_IsoXmitIntMaskSet, ~0);
ohci->it_context_support = reg_read(ohci, OHCI1394_IsoXmitIntMaskSet);
+ /* JMicron JMB38x often shows 0 at first read, just ignore it */
+ if (!ohci->it_context_support) {
+ ohci_notice(ohci, "overriding IsoXmitIntMask\n");
+ ohci->it_context_support = 0xf;
+ }
reg_write(ohci, OHCI1394_IsoXmitIntMaskClear, ~0);
ohci->it_context_mask = ohci->it_context_support;
ohci->n_it = hweight32(ohci->it_context_mask);

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