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authorAlan Stern <stern@rowland.harvard.edu>2008-10-09 15:40:23 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2008-10-17 14:41:04 -0700
commit71b7497c078a97e2afb774ad7c1f8ff5bdda8a60 (patch)
tree149cf8cdb985760ef2afea54bfc5181088311caa /drivers/usb/class/usbtmc.c
parent8b6346ec899713a90890c9e832f7eff91ea73504 (diff)
USB: OHCI: fix endless polling behavior
This patch (as1149) fixes an obscure problem in OHCI polling. In the current code, if the RHSC interrupt status flag turns on at a time when RHSC interrupts are disabled, it will remain on forever: The interrupt handler is the only place where RHSC status gets turned back off; The interrupt handler won't turn RHSC status off because it doesn't turn off status flags if the corresponding interrupt isn't enabled; RHSC interrupts will never get enabled because ohci_root_hub_state_changes() doesn't reenable RHSC if RHSC status is on! As a result we will continue polling indefinitely instead of reverting to interrupt-driven operation, and the root hub will not autosuspend. This particular sequence of events is not at all unusual; in fact plugging a USB device into an OHCI controller will usually cause it to occur. Of course, this is a bug. The proper thing to do is to turn off RHSC status just before reading the actual port status values. That way either a port status change will be detected (if it occurs before the status read) or it will turn RHSC back on. Possibly both, but that won't hurt anything. We can still check for systems in which RHSC is totally broken, by re-reading RHSC after clearing it and before reading the port statuses. (This re-read has to be done anyway, to post the earlier write.) If RHSC is on but no port-change statuses are set, then we know that RHSC is broken and we can avoid re-enabling it. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Cc: stable <stable@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'drivers/usb/class/usbtmc.c')
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