[PATCH v5 12/23] iommu: add a timeout parameter for prq response

[Jacob Pan <jacob.jun.pan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

When an IO page request is processed outside IOMMU subsystem, response can be
delayed or lost. Add a tunable setup parameter such that user can chooose
the timeout for IOMMU to track pending page requests.
This timeout mechanism is a basic safty net which can be implemented in conjunction
with credit based or device level page response exception handling.

Signed-off-by: Jacob Pan <jacob.jun.pan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
---
 Documentation/admin-guide/kernel-parameters.txt |  8 +++++++
 drivers/iommu/iommu.c                           | 28 +++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 11fc28e..5c1e836 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1718,6 +1718,14 @@
 			1 - Bypass the IOMMU for DMA.
 			unset - Use IOMMU translation for DMA.
 
+	iommu.prq_timeout=
+			Timeout in seconds to wait for page response
+			of a pending page request.
+			Format: <integer>
+			Default: 10
+			0 - no timeout tracking
+			1 to 100 - allowed range
+
 	io7=		[HW] IO7 for Marvel based alpha systems
 			See comment before marvel_specify_io7 in
 			arch/alpha/kernel/core_marvel.c.
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 784e019..3a49b96 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -37,6 +37,18 @@
 static struct kset *iommu_group_kset;
 static DEFINE_IDA(iommu_group_ida);
 static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
+/*
+ * Timeout to wait for page response of a pending page request. This is
+ * intended as a basic safty net in case a pending page request is not
+ * responded for an exceptionally long time. Device may also implement
+ * its own protection mechanism against this exception.
+ * Units are in jiffies with a range between 1 - 100 seconds equivalent.
+ * Default to 10 seconds.
+ * Setting 0 means no timeout tracking.
+ */
+#define IOMMU_PAGE_RESPONSE_MAX_TIMEOUT (HZ * 100)
+#define IOMMU_PAGE_RESPONSE_DEF_TIMEOUT (HZ * 10)
+static unsigned long prq_timeout = IOMMU_PAGE_RESPONSE_DEF_TIMEOUT;
 
 struct iommu_callback_data {
 	const struct iommu_ops *ops;
@@ -125,6 +137,22 @@ static int __init iommu_set_def_domain_type(char *str)
 }
 early_param("iommu.passthrough", iommu_set_def_domain_type);
 
+static int __init iommu_set_prq_timeout(char *str)
+{
+	unsigned long timeout;
+
+	if (!str)
+		return -EINVAL;
+	timeout = simple_strtoul(str, NULL, 0);
+	timeout = timeout * HZ;
+	if (timeout > IOMMU_PAGE_RESPONSE_MAX_TIMEOUT)
+		return -EINVAL;
+	prq_timeout = timeout;
+
+	return 0;
+}
+early_param("iommu.prq_timeout", iommu_set_prq_timeout);
+
 static ssize_t iommu_group_attr_show(struct kobject *kobj,
 				     struct attribute *__attr, char *buf)
 {
-- 
2.7.4