[PATCH v2 0/2] Support reading Subsystem ID from Device Tree

[PATCH v2 0/2] Support reading Subsystem ID from Device Tree

[Stefan Binding]

In PC systems using ACPI, the driver is able to read back an SSID from
the _SUB property. This SSID uniquely identifies the system, which
enables the driver to read the correct firmware and tuning for that
system from linux-firmware. Currently there is no way of reading this
property from device tree. Add an equivalent property in device tree
to perform the same role.

Changes since v1:
- Fixed device tree property type

Stefan Binding (2):
  ASoC: dt-bindings: cirrus,cs35l41: Document the cirrus,subsystem-id
    property
  ASoC: cs35l41: Fallback to reading Subsystem ID property if not ACPI

 .../bindings/sound/cirrus,cs35l41.yaml        |  6 ++
 sound/soc/codecs/cs35l41.c                    | 77 +++++++++++--------
 2 files changed, 50 insertions(+), 33 deletions(-)

-- 
2.43.0

[PATCH v2 1/2] ASoC: dt-bindings: cirrus,cs35l41: Document the cirrus,subsystem-id property

[Stefan Binding]

Add new property: cirrus,subsystem-id
This new property is used to uniquely identify the system if device
tree is used, to allow the driver to select the correct firmware and
tuning for the system.

Signed-off-by: Stefan Binding <sbinding@opensource.cirrus.com>
---
 Documentation/devicetree/bindings/sound/cirrus,cs35l41.yaml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/sound/cirrus,cs35l41.yaml b/Documentation/devicetree/bindings/sound/cirrus,cs35l41.yaml
index 14dea1feefc5..e6cf2ebcd777 100644
--- a/Documentation/devicetree/bindings/sound/cirrus,cs35l41.yaml
+++ b/Documentation/devicetree/bindings/sound/cirrus,cs35l41.yaml
@@ -151,6 +151,12 @@ properties:
     minimum: 0
     maximum: 5
 
+  cirrus,subsystem-id:
+    $ref: /schemas/types.yaml#/definitions/string
+    description:
+      Subsystem ID. If this property is present, it sets the system name,
+      used to identify the firmware and tuning to load.
+
 required:
   - compatible
   - reg
-- 
2.43.0

[PATCH v2 2/2] ASoC: cs35l41: Fallback to reading Subsystem ID property if not ACPI

[Stefan Binding]

If ACPI is not used, then there is currently no way of reading a
Subsystem ID property used for a system name to uniquely identify
the system in order to load the correct firmware and tuning.
Add a new property which can be read from device tree to be able to set
the system name.

Signed-off-by: Stefan Binding <sbinding@opensource.cirrus.com>
---
 sound/soc/codecs/cs35l41.c | 77 ++++++++++++++++++++++----------------
 1 file changed, 44 insertions(+), 33 deletions(-)

diff --git a/sound/soc/codecs/cs35l41.c b/sound/soc/codecs/cs35l41.c
index 224d65987a8d..d7e3d89de652 100644
--- a/sound/soc/codecs/cs35l41.c
+++ b/sound/soc/codecs/cs35l41.c
@@ -7,6 +7,7 @@
 // Author: David Rhodes <david.rhodes@cirrus.com>
 
 #include <linux/acpi.h>
+#include <acpi/acpi_bus.h>
 #include <linux/delay.h>
 #include <linux/err.h>
 #include <linux/init.h>
@@ -1147,45 +1148,55 @@ static int cs35l41_dsp_init(struct cs35l41_private *cs35l41)
 	return ret;
 }
 
-#ifdef CONFIG_ACPI
-static int cs35l41_acpi_get_name(struct cs35l41_private *cs35l41)
+static int cs35l41_get_system_name(struct cs35l41_private *cs35l41)
 {
 	struct acpi_device *adev = ACPI_COMPANION(cs35l41->dev);
-	acpi_handle handle = acpi_device_handle(adev);
-	const char *hid;
-	const char *sub;
-
-	/* If there is no acpi_device, there is no ACPI for this system, return 0 */
-	if (!adev)
-		return 0;
+	const char *sub = NULL;
+	const char *tmp;
+	int ret = 0;
 
-	sub = acpi_get_subsystem_id(handle);
-	if (IS_ERR(sub)) {
-		/* If no _SUB, fallback to _HID, otherwise fail */
-		if (PTR_ERR(sub) == -ENODATA) {
-			hid = acpi_device_hid(adev);
-			/* If dummy hid, return 0 and fallback to legacy firmware path */
-			if (!strcmp(hid, "device"))
-				return 0;
-			sub = kstrdup(hid, GFP_KERNEL);
-			if (!sub)
-				sub = ERR_PTR(-ENOMEM);
-
-		} else
-			return PTR_ERR(sub);
+	/* If there is no acpi_device, there is no ACPI for this system, skip checking ACPI */
+	if (adev) {
+		acpi_handle handle = acpi_device_handle(adev);
+
+		sub = acpi_get_subsystem_id(handle);
+		ret = PTR_ERR(sub);
+		if (ret) {
+			sub = NULL;
+			/* If no _SUB, fallback to _HID, otherwise fail */
+			if (ret == -ENODATA) {
+				tmp = acpi_device_hid(adev);
+				/* If dummy hid, return 0 and fallback to legacy firmware path */
+				if (!strcmp(tmp, "device")) {
+					ret = 0;
+					goto err;
+				}
+				sub = kstrdup(tmp, GFP_KERNEL);
+				if (!sub) {
+					ret = -ENOMEM;
+					goto err;
+				}
+			}
+		}
+	} else {
+		if (!device_property_read_string(cs35l41->dev, "cirrus,subsystem-id", &tmp)) {
+			sub = kstrdup(tmp, GFP_KERNEL);
+			if (!sub) {
+				ret = -ENOMEM;
+				goto err;
+			}
+		}
 	}
 
-	cs35l41->dsp.system_name = sub;
-	dev_dbg(cs35l41->dev, "Subsystem ID: %s\n", cs35l41->dsp.system_name);
+err:
+	if (sub) {
+		cs35l41->dsp.system_name = sub;
+		dev_info(cs35l41->dev, "Subsystem ID: %s\n", cs35l41->dsp.system_name);
+	} else
+		dev_warn(cs35l41->dev, "Subsystem ID not found\n");
 
-	return 0;
-}
-#else
-static int cs35l41_acpi_get_name(struct cs35l41_private *cs35l41)
-{
-	return 0;
+	return ret;
 }
-#endif /* CONFIG_ACPI */
 
 int cs35l41_probe(struct cs35l41_private *cs35l41, const struct cs35l41_hw_cfg *hw_cfg)
 {
@@ -1317,7 +1328,7 @@ int cs35l41_probe(struct cs35l41_private *cs35l41, const struct cs35l41_hw_cfg *
 		goto err;
 	}
 
-	ret = cs35l41_acpi_get_name(cs35l41);
+	ret = cs35l41_get_system_name(cs35l41);
 	if (ret < 0)
 		goto err;
 
-- 
2.43.0

Re: [PATCH v2 1/2] ASoC: dt-bindings: cirrus,cs35l41: Document the cirrus,subsystem-id property

[Krzysztof Kozlowski]

On 12/09/2025 17:47, Stefan Binding wrote:
> Add new property: cirrus,subsystem-id
> This new property is used to uniquely identify the system if device
> tree is used, to allow the driver to select the correct firmware and
> tuning for the system.
> 
> Signed-off-by: Stefan Binding <sbinding@opensource.cirrus.com>
> ---
>  Documentation/devicetree/bindings/sound/cirrus,cs35l41.yaml | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/sound/cirrus,cs35l41.yaml b/Documentation/devicetree/bindings/sound/cirrus,cs35l41.yaml
> index 14dea1feefc5..e6cf2ebcd777 100644
> --- a/Documentation/devicetree/bindings/sound/cirrus,cs35l41.yaml
> +++ b/Documentation/devicetree/bindings/sound/cirrus,cs35l41.yaml
> @@ -151,6 +151,12 @@ properties:
>      minimum: 0
>      maximum: 5
>  
> +  cirrus,subsystem-id:
> +    $ref: /schemas/types.yaml#/definitions/string
> +    description:
> +      Subsystem ID. If this property is present, it sets the system name,
> +      used to identify the firmware and tuning to load.

Please do not send new version immediately, but allow people to actually
review your code. You received the review on v1.

Best regards,
Krzysztof