Date: Wed, 10 Jul 2013 12:59:40 -0700 From: Marcel Moolenaar <marcel@xcllnt.net> To: John Baldwin <jhb@FreeBSD.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, Marcel Moolenaar <marcel@freebsd.org>, src-committers@freebsd.org Subject: Re: svn commit: r253161 - head/sys/dev/uart Message-ID: <BF25167F-A24A-479E-85C7-6D47588DEDAD@xcllnt.net> In-Reply-To: <201307101409.42228.jhb@freebsd.org> References: <201307101742.r6AHgKOm024113@svn.freebsd.org> <201307101405.44158.jhb@freebsd.org> <201307101409.42228.jhb@freebsd.org>
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On Jul 10, 2013, at 11:09 AM, John Baldwin <jhb@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 >>>=20 >>> 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. >>=20 >> 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. --=20 Marcel Moolenaar marcel@xcllnt.net
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