On Jul 11, 2013, at 6:41 AM, John Baldwin <j...@freebsd.org> wrote: > On Wednesday, July 10, 2013 3:59:40 pm Marcel Moolenaar wrote: >> >> On Jul 10, 2013, at 11:09 AM, John Baldwin <j...@freebsd.org> wrote: >> >>> On Wednesday, July 10, 2013 2:05:43 pm John Baldwin wrote: >>>> On Wednesday, July 10, 2013 1:42:20 pm Marcel Moolenaar wrote: >>>>> Author: marcel >>>>> Date: Wed Jul 10 17:42:20 2013 >>>>> New Revision: 253161 >>>>> URL: http://svnweb.freebsd.org/changeset/base/253161 >>>>> >>>>> Log: >>>>> Protect against broken hardware. In this particular case, protect against >>>>> H/W not de-asserting the interrupt at all. On x86, and because of the >>>>> following conditions, this results in a hard hang with interrupts >>>>> disabled: >>>>> 1. The uart(4) driver uses a spin lock to protect against concurrent >>>>> access to the H/W. Spin locks disable and restore interrupts. >>>>> 2. Restoring the interrupt on x86 always writes the flags register. Even >>>>> if we're restoring the interrupt from disabled to disabled. >>>>> 3. The x86 CPU has a short window in which interrupts are enabled when >>>>> the >>>>> flags register is written. >>>> >>>> Do you have proof of this? >> >> No. I only have proof of a hard hang during auto configuration that >> cannot be fixed in any other way than not to setup the interrupt at >> all. > > Ok. I think what is happening is that you are just spinning in the interrupt > handler forever due to the hardware being stuck in that case in the old code. > I assume you tried just using the count first but it still hung? (Perhaps the > interrupt was for a PCI device and level-triggered and so it kept reasserting > anyway?)
Yes, the count alone didn't do the trick. It's really a H/W problem. I suspect a floating line to an FPGA. The condition is cleared by means that go beyond FreeBSD, let me put it that way :-) > I think your change is correct for a uart that is stuck in this way > regardless, > I just think the hang isn't related to weirdness with x86 temporarily > re-enabling interrupts. You're right. I looked at configure() this time and it starts with enable_intr(). For some reason I had it in my head that we auto-configure with interrupts disabled. We do on most platforms, just not on x86... -- Marcel Moolenaar mar...@xcllnt.net _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
