linux-kernel - [PATCH] iommu/vt-d: Don't store SIRTP request

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Message-ID: <53E8A555.5010905@siemens.com>
Date:	Mon, 11 Aug 2014 13:13:25 +0200
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Joerg Roedel <joro@...tes.org>,
	iommu <iommu@...ts.linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
CC:	Jiang Liu <jiang.liu@...ux.intel.com>
Subject: [PATCH] iommu/vt-d: Don't store SIRTP request

Don't store the SIRTP request bit in the register state. It will
otherwise become sticky and could request an Interrupt Remap Table
Pointer update on each command register write.

Found while starting to emulate IR in QEMU, not by observing problems on
real hardware.

Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
---
 drivers/iommu/intel_irq_remapping.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/iommu/intel_irq_remapping.c b/drivers/iommu/intel_irq_remapping.c
index 0df41f6..a872874 100644
--- a/drivers/iommu/intel_irq_remapping.c
+++ b/drivers/iommu/intel_irq_remapping.c
@@ -438,8 +438,7 @@ static void iommu_set_irq_remapping(struct intel_iommu *iommu, int mode)
 		    (addr) | IR_X2APIC_MODE(mode) | INTR_REMAP_TABLE_REG_SIZE);
 
 	/* Set interrupt-remapping table pointer */
-	iommu->gcmd |= DMA_GCMD_SIRTP;
-	writel(iommu->gcmd, iommu->reg + DMAR_GCMD_REG);
+	writel(iommu->gcmd | DMA_GCMD_SIRTP, iommu->reg + DMAR_GCMD_REG);
 
 	IOMMU_WAIT_OP(iommu, DMAR_GSTS_REG,
 		      readl, (sts & DMA_GSTS_IRTPS), sts);
-- 
1.8.1.1.298.ge7eed54
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