From 8da854cb02156c90028233ae1e85ce46a1d3f82c Mon Sep 17 00:00:00 2001 From: "Pallipadi, Venkatesh" Date: Thu, 25 Feb 2010 10:53:48 -0800 Subject: [PATCH] x86, hpet: Erratum workaround for read after write of HPET comparator On Wed, Feb 24, 2010 at 03:37:04PM -0800, Justin Piszcz wrote: > Hello, > > Again, on the Intel DP55KG board: > > # uname -a > Linux host 2.6.33 #1 SMP Wed Feb 24 18:31:00 EST 2010 x86_64 GNU/Linux > > [ 1.237600] ------------[ cut here ]------------ > [ 1.237890] WARNING: at arch/x86/kernel/hpet.c:404 hpet_next_event+0x70/0x80() > [ 1.238221] Hardware name: > [ 1.238504] hpet: compare register read back failed. > [ 1.238793] Modules linked in: > [ 1.239315] Pid: 0, comm: swapper Not tainted 2.6.33 #1 > [ 1.239605] Call Trace: > [ 1.239886] [] ? warn_slowpath_common+0x73/0xb0 > [ 1.240409] [] ? tick_dev_program_event+0x38/0xc0 > [ 1.240699] [] ? warn_slowpath_fmt+0x40/0x50 > [ 1.240992] [] ? tick_dev_program_event+0x38/0xc0 > [ 1.241281] [] ? hpet_next_event+0x70/0x80 > [ 1.241573] [] ? tick_dev_program_event+0x38/0xc0 > [ 1.241859] [] ? tick_handle_oneshot_broadcast+0xe2/0x100 > [ 1.246533] [] ? timer_interrupt+0x1a/0x30 > [ 1.246826] [] ? handle_IRQ_event+0x39/0xd0 > [ 1.247118] [] ? handle_edge_irq+0xb8/0x160 > [ 1.247407] [] ? handle_irq+0x15/0x20 > [ 1.247689] [] ? do_IRQ+0x62/0xe0 > [ 1.247976] [] ? ret_from_intr+0x0/0xa > [ 1.248262] [] ? mwait_idle+0x57/0x80 > [ 1.248796] [] ? cpu_idle+0x5c/0xb0 > [ 1.249080] ---[ end trace db7f668fb6fef4e1 ]--- > > Is this something Intel has to fix or is it a bug in the kernel? This is a chipset erratum. Thomas: You mentioned we can retain this check only for known-buggy and hpet debug kind of options. But here is the simple workaround patch for this particular erratum. Some chipsets have a erratum due to which read immediately following a write of HPET comparator returns old comparator value instead of most recently written value. Erratum 15 in "Intel I/O Controller Hub 9 (ICH9) Family Specification Update" (http://www.intel.com/assets/pdf/specupdate/316973.pdf) Workaround for the errata is to read the comparator twice if the first one fails. Signed-off-by: Venkatesh Pallipadi LKML-Reference: <20100225185348.GA9674@linux-os.sc.intel.com> Signed-off-by: H. Peter Anvin Cc: Venkatesh Pallipadi Cc: --- arch/x86/kernel/hpet.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index ee4fa1bfcb33..3d422da92100 100644 --- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -399,9 +399,15 @@ static int hpet_next_event(unsigned long delta, * then we might have a real hardware problem. We can not do * much about it here, but at least alert the user/admin with * a prominent warning. + * An erratum on some chipsets (ICH9,..), results in comparator read + * immediately following a write returning old value. Workaround + * for this is to read this value second time, when first + * read returns old value. */ - WARN_ONCE(hpet_readl(HPET_Tn_CMP(timer)) != cnt, + if (unlikely((u32)hpet_readl(HPET_Tn_CMP(timer)) != cnt)) { + WARN_ONCE(hpet_readl(HPET_Tn_CMP(timer)) != cnt, KERN_WARNING "hpet: compare register read back failed.\n"); + } return (s32)(hpet_readl(HPET_COUNTER) - cnt) >= 0 ? -ETIME : 0; } -- 2.30.2