linux-kernel - Make intel iommu_wait_op work with jiffies arn't running

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Message-ID: <20080508184054.GA20557@linux.intel.com>
Date:	Thu, 8 May 2008 11:40:54 -0700
From:	mark gross <mgross@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>, Greg KH <greg@...ah.com>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: Make intel iommu_wait_op work with jiffies arn't running

I've noticed that a few times when the bios is buggy the code for
detecting failing DMAR hardware can get stuck in an infinite loop in
early boot waiting for jiffies to time out.  Which are not running at
the time we get stuck in this macro.

This patch replaces the use of the jiffies to detect the failing
hardware with the tsc counter.  Not a big change, instead of getting a
black screen forever, you get a panic...

I also changed the time out from an arbitrary 60 seconds to an arbitrary
10 seconds.

--mgross

Signed-Off-by: mark gross <mgross@...ux.intel.com>


Index: linux-next/drivers/pci/intel-iommu.c
===================================================================
--- linux-next.orig/drivers/pci/intel-iommu.c	2008-05-08 11:02:21.000000000 -0700
+++ linux-next/drivers/pci/intel-iommu.c	2008-05-08 11:13:02.000000000 -0700
@@ -49,7 +49,7 @@
 
 #define DEFAULT_DOMAIN_ADDRESS_WIDTH 48
 
-#define DMAR_OPERATION_TIMEOUT (HZ*60) /* 1m */
+#define DMAR_OPERATION_TIMEOUT ((cycles_t) tsc_khz*10*1000) /* 10sec */
 
 #define DOMAIN_MAX_ADDR(gaw) ((((u64)1) << gaw) - 1)
 
@@ -490,13 +490,13 @@
 
 #define IOMMU_WAIT_OP(iommu, offset, op, cond, sts) \
 {\
-	unsigned long start_time = jiffies;\
+	cycles_t start_time = get_cycles();\
 	while (1) {\
 		sts = op (iommu->reg + offset);\
 		if (cond)\
 			break;\
-		if (time_after(jiffies, start_time + DMAR_OPERATION_TIMEOUT))\
-			panic("DMAR hardware is malfunctioning\n");\
+		if (DMAR_OPERATION_TIMEOUT < (get_cycles() - start_time))\
+			panic(KERN_ERR "DMAR hardware is malfunctioning\n");\
 		cpu_relax();\
 	}\
 }
--
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