regulator: scmi: add support for registering SCMI regulators by name

Add support to register SCMI regulator subnodes based on an SCMI Voltage Domain name specified via the 'regulator-name' device tree property. In doing so, make the 'reg' property optional with the constraint that at least one of 'reg' or 'regulator-name' must be specified. If both are specified, then both must match the Voltage Domain data exposed by the SCMI platform.

Name based SCMI regulator registration helps ensure that an SCMI agent doesn't need to be aware of the numbering scheme used for Voltage Domains by the SCMI platform. It also ensures that the correct Voltage Domain is selected for a given physical regulator. This cannot be guaranteed with numeric Voltage Domain IDs alone.

David Collins (2):
dt-bindings: firmware: arm,scmi: define support for name based
regulators
regulator: scmi: add support for registering SCMI regulators by name

 .../bindings/firmware/arm,scmi.yaml           | 11 +++-
 drivers/regulator/scmi-regulator.c            | 57 ++++++++++++++++++-
 2 files changed, 62 insertions(+), 6 deletions(-)

2.17.1

Allow SCMI regulator subnodes to be specified either by ID using the "reg" property or by name using the "regulator-name" property.

Name based SCMI regulator specification helps ensure that an SCMI agent doesn't need to be aware of the numbering scheme used for Voltage Domains by the SCMI platform. It also ensures that the correct Voltage Domain is selected for a given physical regulator. This cannot be guaranteed with numeric Voltage Domain IDs alone.

---
 .../devicetree/bindings/firmware/arm,scmi.yaml        | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

index 5c4c6782e052..bc4a84fe25d2 100644
@@ -155,7 +155,7 @@ properties:
           The list of all regulators provided by this SCMI controller.
 
         patternProperties:
-          '^regulators@[0-9a-f]+$':
+          '^regulator.+$':
             type: object
             $ref: "../regulator/regulator.yaml#"
 

@@ -164,8 +164,13 @@ properties:
                 maxItems: 1
                 description: Identifier for the voltage regulator.
 
-            required:
-              - reg
+              regulator-name: true
+
+            anyOf:
+              - required:
+                  - reg
+              - required:
+                  - regulator-name
 
 additionalProperties: false
 

2.17.1

What is a "SCMI agent" in this context? This is changing how the DT bindings are specified, at some point things are going to need to be hard coded.

An SCMI agent is the entity that issues SCMI commands (i.e. the consumer). An SCMI platform is the entity that receives the SCMI commands and performs the necessary operations (i.e. the provider). This is the terminology used in the ARM SCMI spec [1].

A typical system layout could have an agent that is the application processor (running Linux) and a platform that is an embedded controller.

The system layout that this patch is targeted for consists of an SCMI platform implemented in software in the primary Linux OS on the application processor and an SCMI agent in a guest VM (also running Linux). This provides paravirtualized regulator control to the guest VM where full virtualization is not supported.

During the course of development of these software images, it may be necessary to add or reorder the set of SCMI voltage domains (regulators) implemented on the platform side. If the voltage domains are only identified and matched based on the ID number, then it is easy for the platform and agent to get out of sync.

Using the voltage domain name instead of ID number for identification and matching provides robust assurance of correct regulator usage in the face of domains being added, removed, or reordered on the platform side.

Would you be ok with a new DT property being added in place of "regulator-name" in this patch which serves the same matching purpose (perhaps "arm,scmi-domain-name")?

Thanks,
David

[1]: https://developer.arm.com/documentation/den0056/latest

This seems like a scenario where the DT should be being generated at runtime along with the virtualisation of the platform? TBH a setup where this is an issue feels like it's asking for trouble.

Yes, it needs to be a new property.

I'm not familiar with runtime device tree generation. Could you please point to an example of it or documentation for it? How would this handle kernel devices on the VM side which need a phandle to an scmi-regulator DT subnode in order to get a pointer to the corresponding regulator device at runtime via devm_regulator_get()?

Ok, I'll modify the series in V2 to use a different property.

Thanks,
David

I believe qemu does this for the virt machine. I'm not sure what you're seeing as particularly complex about generating regulator links in particular though?

Add support to register SCMI regulator subnodes based on an SCMI Voltage Domain name specified via the 'regulator-name' device tree property. In doing so, make the 'reg' property optional with the constraint that at least one of 'reg' or 'regulator-name' must be specified. If both are specified, then both must match the Voltage Domain data exposed by the SCMI platform.

Name based SCMI regulator registration helps ensure that an SCMI agent doesn't need to be aware of the numbering scheme used for Voltage Domains by the SCMI platform. It also ensures that the correct Voltage Domain is selected for a given physical regulator. This cannot be guaranteed with numeric Voltage Domain IDs alone.

---
 drivers/regulator/scmi-regulator.c | 57 ++++++++++++++++++++++++++++--
 1 file changed, 54 insertions(+), 3 deletions(-)

index 1f02f60ad136..c3287901975e 100644
@@ -31,6 +31,7 @@
 #include <linux/regulator/of_regulator.h>
 #include <linux/scmi_protocol.h>
 #include <linux/slab.h>
+#include <linux/string.h>
 #include <linux/types.h>
 
 static const struct scmi_voltage_proto_ops *voltage_ops;

@@ -252,16 +253,66 @@ static int scmi_regulator_common_init(struct scmi_regulator *sreg)
 	return 0;
 }
 
+static int scmi_regulator_map_name(struct scmi_protocol_handle *ph,
+				   struct scmi_regulator_info *rinfo,
+				   const char *name)
+{
+	const struct scmi_voltage_info *vinfo;
+	int i;
+
+	for (i = 0; i < rinfo->num_doms; i++) {
+		vinfo = voltage_ops->info_get(ph, i);
+		if (!vinfo)
+			continue;
+		if (!strncmp(vinfo->name, name, sizeof(vinfo->name)))
+			return i;
+	}
+
+	return -ENODEV;
+}
+
 static int process_scmi_regulator_of_node(struct scmi_device *sdev,
 					  struct scmi_protocol_handle *ph,
 					  struct device_node *np,
 					  struct scmi_regulator_info *rinfo)
 {
 	u32 dom, ret;
+	int name_dom;
+	const char *name;
 
-	ret = of_property_read_u32(np, "reg", &dom);
-	if (ret)
-		return ret;
+	dom = rinfo->num_doms;
+	if (of_find_property(np, "reg", NULL)) {
+		ret = of_property_read_u32(np, "reg", &dom);
+		if (ret)
+			return ret;
+
+		if (dom >= rinfo->num_doms)
+			return -ENODEV;
+	}
+
+	if (of_find_property(np, "regulator-name", NULL)) {
+		ret = of_property_read_string(np, "regulator-name", &name);
+		if (ret)
+			return ret;
+
+		name_dom = scmi_regulator_map_name(ph, rinfo, name);
+		if (name_dom < 0) {
+			dev_err(&sdev->dev,
+				"No SCMI Voltage Domain found named %s. Skipping: %s\n",
+				name, np->full_name);
+			return name_dom;
+		}
+
+		if (dom >= rinfo->num_doms)
+			dom = name_dom;
+
+		if (name_dom != dom) {
+			dev_err(&sdev->dev,
+				"SCMI Voltage Domain %s ID mismatch, %u (DT) != %d (firmware). Skipping: %s\n",
+				name, dom, name_dom, np->full_name);
+			return -EINVAL;
+		}
+	}
 
 	if (dom >= rinfo->num_doms)
 		return -ENODEV;

2.17.1


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