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

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

[Jan Kiszka]

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@siemens.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

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

[Joerg Roedel]

On Mon, Aug 11, 2014 at 01:13:25PM +0200, Jan Kiszka wrote:
> 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@siemens.com>
> ---
>  drivers/iommu/intel_irq_remapping.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)

Applied, thanks Jan.