From 2231e5748746cd57df389521397e1c7f91882077 Mon Sep 17 00:00:00 2001
From: David Woodhouse <David.Woodhouse@intel.com>
Date: Mon, 15 Feb 2016 12:42:38 +0000
Subject: [PATCH] iommu/vt-d: Clear PPR bit to ensure we get more page request
interrupts
commit 46924008273ed03bd11dbb32136e3da4cfe056e1 upstream.
According to the VT-d specification we need to clear the PPR bit in
the Page Request Status register when handling page requests, or the
hardware won't generate any more interrupts.
This wasn't actually necessary on SKL/KBL (which may well be the
subject of a hardware erratum, although it's harmless enough). But
other implementations do appear to get it right, and we only ever get
one interrupt unless we clear the PPR bit.
Reported-by: CQ Tang <cq.tang@intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/iommu/intel-svm.c | 4 ++++
include/linux/intel-iommu.h | 3 +++
2 files changed, 7 insertions(+)
diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
index 97a818992d6d..d9939fa9b588 100644
--- a/drivers/iommu/intel-svm.c
+++ b/drivers/iommu/intel-svm.c
@@ -524,6 +524,10 @@ static irqreturn_t prq_event_thread(int irq, void *d)
struct intel_svm *svm = NULL;
int head, tail, handled = 0;
+ /* Clear PPR bit before reading head/tail registers, to
+ * ensure that we get a new interrupt if needed. */
+ writel(DMA_PRS_PPR, iommu->reg + DMAR_PRS_REG);
+
tail = dmar_readq(iommu->reg + DMAR_PQT_REG) & PRQ_RING_MASK;
head = dmar_readq(iommu->reg + DMAR_PQH_REG) & PRQ_RING_MASK;
while (head != tail) {
diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
index 821273ca4873..2d9b650047a5 100644
--- a/include/linux/intel-iommu.h
+++ b/include/linux/intel-iommu.h
@@ -235,6 +235,9 @@ static inline void dmar_writeq(void __iomem *addr, u64 val)
/* low 64 bit */
#define dma_frcd_page_addr(d) (d & (((u64)-1) << PAGE_SHIFT))
+/* PRS_REG */
+#define DMA_PRS_PPR ((u32)1)
+
#define IOMMU_WAIT_OP(iommu, offset, op, cond, sts) \
do { \
cycles_t start_time = get_cycles(); \
--
2.34.1