[PATCH v2 18/31] iommu/vt-d: Cache max domain ID to avoid redundant calculation

[Xu Yilun <yilun.xu@linux.intel.com>]

From: Lu Baolu <baolu.lu@linux.intel.com>

The cap_ndoms() helper calculates the maximum available domain ID from
the value of capability register, which can be inefficient if called
repeatedly. Cache the maximum supported domain ID in max_domain_id field
during initialization to avoid redundant calls to cap_ndoms() throughout
the IOMMU driver.

No functionality change.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>
---
 drivers/iommu/intel/iommu.h |  1 +
 drivers/iommu/intel/dmar.c  |  1 +
 drivers/iommu/intel/iommu.c | 10 +++++-----
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
index 599913fb65d5..4a21ab6a311d 100644
--- a/drivers/iommu/intel/iommu.h
+++ b/drivers/iommu/intel/iommu.h
@@ -705,6 +705,7 @@ struct intel_iommu {
 	/* mutex to protect domain_ida */
 	struct mutex	did_lock;
 	struct ida	domain_ida; /* domain id allocator */
+	unsigned long	max_domain_id;
 	unsigned long	*copied_tables; /* bitmap of copied tables */
 	spinlock_t	lock; /* protect context, domain ids */
 	struct root_entry *root_entry; /* virtual address */
diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index d68c06025cac..93efd1a5dc5b 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -1099,6 +1099,7 @@ static int alloc_iommu(struct dmar_drhd_unit *drhd)
 	spin_lock_init(&iommu->lock);
 	ida_init(&iommu->domain_ida);
 	mutex_init(&iommu->did_lock);
+	iommu->max_domain_id = cap_ndoms(iommu->cap);
 
 	ver = readl(iommu->reg + DMAR_VER_REG);
 	pr_info("%s: reg_base_addr %llx ver %d:%d cap %llx ecap %llx\n",
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index ef7613b177b9..9a57f78647ed 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1043,7 +1043,7 @@ int domain_attach_iommu(struct dmar_domain *domain, struct intel_iommu *iommu)
 	}
 
 	num = ida_alloc_range(&iommu->domain_ida, IDA_START_DID,
-			      cap_ndoms(iommu->cap) - 1, GFP_KERNEL);
+			      iommu->max_domain_id - 1, GFP_KERNEL);
 	if (num < 0) {
 		pr_err("%s: No free domain ids\n", iommu->name);
 		goto err_unlock;
@@ -1107,7 +1107,7 @@ static void copied_context_tear_down(struct intel_iommu *iommu,
 	did_old = context_domain_id(context);
 	context_clear_entry(context);
 
-	if (did_old < cap_ndoms(iommu->cap)) {
+	if (did_old < iommu->max_domain_id) {
 		iommu->flush.flush_context(iommu, did_old,
 					   PCI_DEVID(bus, devfn),
 					   DMA_CCMD_MASK_NOBIT,
@@ -1505,7 +1505,7 @@ static int copy_context_table(struct intel_iommu *iommu,
 			continue;
 
 		did = context_domain_id(&ce);
-		if (did >= 0 && did < cap_ndoms(iommu->cap))
+		if (did >= 0 && did < iommu->max_domain_id)
 			ida_alloc_range(&iommu->domain_ida, did, did, GFP_KERNEL);
 
 		set_context_copied(iommu, bus, devfn);
@@ -2425,7 +2425,7 @@ static ssize_t domains_supported_show(struct device *dev,
 				      struct device_attribute *attr, char *buf)
 {
 	struct intel_iommu *iommu = dev_to_intel_iommu(dev);
-	return sysfs_emit(buf, "%ld\n", cap_ndoms(iommu->cap));
+	return sysfs_emit(buf, "%ld\n", iommu->max_domain_id);
 }
 static DEVICE_ATTR_RO(domains_supported);
 
@@ -2436,7 +2436,7 @@ static ssize_t domains_used_show(struct device *dev,
 	unsigned int count = 0;
 	int id;
 
-	for (id = 0; id < cap_ndoms(iommu->cap); id++)
+	for (id = 0; id < iommu->max_domain_id; id++)
 		if (ida_exists(&iommu->domain_ida, id))
 			count++;
 
-- 
2.25.1