Hi,
I apologize if this has already been reported, I didn't find anything
with a quick search in the archives. I have been looking at the EHCI
code in 2.6.18 and found this:
In 2.6.18 ehci_irq() [1], starting at line 619 the code looks like this:
/* remote wakeup [4.3.1] */
619 if (status & STS_PCD) {
620 unsigned i = HCS_N_PORTS (ehci->hcs_params);
621
622 /* resume root hub? */
623 status = readl (&ehci->regs->command);
624 if (!(status & CMD_RUN))
625 writel (status | CMD_RUN, &ehci->regs->command);
626
<snip, no assignments to status>
644 }
645
646 /* PCI errors [4.15.2.4] */
647 if (unlikely ((status & STS_FATAL) != 0)) {
648 /* bogus "fatal" IRQs appear on some chips... why? */
649 status = readl (&ehci->regs->status);
650 dbg_cmd (ehci, "fatal", readl (&ehci->regs->command));
651 dbg_status (ehci, "fatal", status);
652 if (status & STS_HALT) {
653 ehci_err (ehci, "fatal error\n");
654 dead:
655 ehci_reset (ehci);
656 writel (0, &ehci->regs->configured_flag);
657 /* generic layer kills/unlinks all urbs, then
658 * uses ehci_stop to clean up the rest
659 */
660 bh = 1;
661 }
662 }
Now, STS_FATAL (Host System Error) is bit 4 in the USBSTS register. If
STS_PCD is set line 623 assigns the status variable with the value of
USBCMD. Which will, sometimes, trigger the status & STS_FATAL
condition since bit 4 in USBCMD is Periodic Schedule Enable.
The problem above was fixed by a patch from Alan Stern [2] "Fix
root-hub and port suspend/resume problems" but I did not find any
comments about the problem above being identified. The code in 2.6.21
still contains:
/* PCI errors [4.15.2.4] */
if (unlikely ((status & STS_FATAL) != 0)) {
/* bogus "fatal" IRQs appear on some chips... why? */
status = ehci_readl(ehci, &ehci->regs->status);
So, if the bogus IRQs were triggered by the assignment of USBCMD to
status above, the comment and the re-reading of USBSTS could perhaps
be removed?
Best regards,
Jan
[1] http://lxr.linux.no/source/drivers/usb/host/ehci-hcd.c?v=2.6.18#L618
[2] http://surl.se/auaz
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