[PATCH v2] iommu/arm-smmu: Add global SMR masking property

[Robin Murphy]

The current SMR masking support using a 2-cell iommu-specifier is
primarily intended to handle individual masters with large and/or
complex Stream ID assignments; it quickly gets a bit clunky in other SMR
use-cases where we just want to consistently mask out the same part of
every Stream ID (e.g. for MMU-500 configurations where the appended TBU
number gets in the way unnecessarily). Let's add a new property to allow
a single global mask value to better fit the latter situation.

Tested-by: Nipun Gupta <nipun.gupta at nxp.com>
Signed-off-by: Robin Murphy <robin.murphy at arm.com>
---

v2: Rewrite the documentation to actually make sense, and add an
    explicit example per Mark's suggestion.

 .../devicetree/bindings/iommu/arm,smmu.txt         | 27 ++++++++++++++++++++++
 drivers/iommu/arm-smmu.c                           |  4 +++-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.txt b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
index 6cdf32d037fc..b744b231766f 100644
--- a/Documentation/devicetree/bindings/iommu/arm,smmu.txt
+++ b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
@@ -60,6 +60,16 @@ conditions.
                   aliases of secure registers have to be used during
                   SMMU configuration.
 
+- stream-match-mask : For SMMUs supporting stream matching and using
+                  #iommu-cells = <1>, specifies a fixed value to set in
+                  the SMRn.MASK field of every stream match register
+                  used, for cases where it is desirable to ignore some
+                  portion of every Stream ID (e.g. for certain MMU-500
+                  configurations given globally unique input IDs). This
+                  property is not valid for SMMUs using stream indexing,
+                  or using stream matching with #iommu-cells = <2>, and
+                  may be ignored if present in such cases.
+
 ** Deprecated properties:
 
 - mmu-masters (deprecated in favour of the generic "iommus" binding) :
@@ -109,3 +119,20 @@ conditions.
         master3 {
                 iommus = <&smmu2 1 0x30>;
         };
+
+
+        /* ARM MMU-500 with 10-bit stream ID input configuration */
+        smmu3: iommu {
+                compatible = "arm,mmu-500", "arm,smmu-v2";
+                ...
+                #iommu-cells = <1>;
+                /* always ignore appended 5-bit TBU number */
+                stream-match-mask = 0x7c00;
+        };
+
+        bus {
+                /* bus whose child devices emit one unique 10-bit stream
+                   ID each, but may master through multiple SMMU TBUs */
+                iommu-map = <0 &smmu3 0 0x400>;
+                ...
+        };
diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index abf6496843a6..e394d55146a6 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -1590,13 +1590,15 @@ static int arm_smmu_domain_set_attr(struct iommu_domain *domain,
 
 static int arm_smmu_of_xlate(struct device *dev, struct of_phandle_args *args)
 {
-	u32 fwid = 0;
+	u32 mask, fwid = 0;
 
 	if (args->args_count > 0)
 		fwid |= (u16)args->args[0];
 
 	if (args->args_count > 1)
 		fwid |= (u16)args->args[1] << SMR_MASK_SHIFT;
+	else if (!of_property_read_u32(args->np, "stream-match-mask", &mask))
+		fwid |= (u16)mask << SMR_MASK_SHIFT;
 
 	return iommu_fwspec_add_ids(dev, &fwid, 1);
 }
-- 
2.11.0.dirty