Add driver to read out SOM id pins (#60)

* add driver to read out som id pins

* fix mistake

arch/arm64/boot/dts/qcom/comma_common.dtsi

@@ -111,6 +111,14 @@
 };
 
 &vendor {
+  gpio-som-id {
+    status="okay";
+    compatible = "comma,gpio-som-id";
+    gpios = <&tlmm 105 0>, <&tlmm 106 0>, <&tlmm 107 0>, <&tlmm 108 0>;
+    pinctrl-names = "default";
+    pinctrl-0 = <&som_id_default>;
+  };
+
   bluetooth: bt_wcn3990 {
     compatible = "qca,wcn3990";
     qca,bt-vdd-io-supply = <&pm8998_s3>;

arch/arm64/boot/dts/qcom/sdm845-pinctrl.dtsi

@@ -21,6 +21,19 @@
 		#interrupt-cells = <2>;
 		interrupt-parent = <&pdc>;
 
+		som_id_default: som_id_default {
+			mux {
+				pins = "gpio105", "gpio106", "gpio107", "gpio108";
+				function = "gpio";
+			};
+
+			config {
+				pins = "gpio105", "gpio106", "gpio107", "gpio108";
+				bias-pull-up;
+				drive-strength = <10>;
+			};
+		};
+
 		ufs_dev_reset_assert: ufs_dev_reset_assert {
 			config {
 				pins = "ufs_reset";

arch/arm64/configs/tici_defconfig

@@ -4304,6 +4304,7 @@ CONFIG_MSM_EXT_DISPLAY=y
 CONFIG_CLKDEV_LOOKUP=y
 CONFIG_HAVE_CLK_PREPARE=y
 CONFIG_COMMON_CLK=y
+CONFIG_GPIO_SOM_ID=y
 
 #
 # Common Clock Framework

drivers/platform/msm/Kconfig

@@ -234,4 +234,12 @@ config MSM_RMNET_BAM
           for routing IP packets within the MSM using
           BAM as a physical transport.
 
+config GPIO_SOM_ID
+	bool "Simple GPIO-based ID driver"
+	help
+		This driver uses the internal pull-ups of the provided GPIOs to
+		detect the SOM ID. The SOM ID is a 4-bit value that is set by
+		tying the GPIOs to either ground or VDD. The SOM ID can then
+		be read in userspace by sysfs.
+
 endmenu

drivers/platform/msm/Makefile

@@ -16,3 +16,4 @@ obj-$(CONFIG_MSM_11AD) += msm_11ad/
 obj-$(CONFIG_SEEMP_CORE) += seemp_core/
 obj-$(CONFIG_QCOM_GENI_SE) += qcom-geni-se.o
 obj-$(CONFIG_MSM_EXT_DISPLAY) += msm_ext_display.o
+obj-$(CONFIG_GPIO_SOM_ID) += gpio_som_id.o

drivers/platform/msm/gpio_som_id.c

@@ -0,0 +1,111 @@
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/of_platform.h>
+#include <linux/gpio/consumer.h>
+#include <linux/sysfs.h>
+
+struct gpio_som_id {
+	struct platform_device *pdev;
+  struct pinctrl *pinctrl;
+  struct gpio_desc *gpio[4];
+};
+
+static ssize_t som_id_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+  struct gpio_som_id *som_id = dev_get_drvdata(dev);
+  int i, id = 0;
+
+  if (!som_id)
+    goto error;
+
+  for (i=0; i<sizeof(som_id->gpio)/sizeof(som_id->gpio[0]); i++) {
+    id |= gpiod_get_value(som_id->gpio[i]) << i;
+  }
+
+  return sprintf(buf, "%d\n", id);
+error:
+  return -EINVAL;
+}
+
+static DEVICE_ATTR_RO(som_id);
+
+static struct attribute *som_id_attrs[] = {
+  &dev_attr_som_id.attr,
+  NULL
+};
+
+static struct attribute_group som_id_attr_group = {
+  .attrs = som_id_attrs,
+};
+
+static int gpio_som_id_probe(struct platform_device *pdev)
+{
+	struct gpio_som_id *som_id;
+	int i, rc = 0;
+
+	som_id = devm_kzalloc(&pdev->dev, sizeof(*som_id), GFP_KERNEL);
+	if (!som_id)
+		return -ENOMEM;
+
+	som_id->pdev = pdev;
+
+  // you need to set a pinctrl for the GPIOs to have pull-ups
+  som_id->pinctrl = devm_pinctrl_get(&pdev->dev);
+  if (IS_ERR(som_id->pinctrl)) {
+    dev_err(&pdev->dev, "Failed to get pinctrl: %ld\n", PTR_ERR(som_id->pinctrl));
+    rc = PTR_ERR(som_id->pinctrl);
+    goto error;
+  }
+
+  // get the GPIOs
+  for (i=0; i<sizeof(som_id->gpio)/sizeof(som_id->gpio[0]); i++) {
+    som_id->gpio[i] = devm_gpiod_get_index(&pdev->dev, NULL, i, GPIOD_IN);
+    if (IS_ERR(som_id->gpio[i])) {
+      dev_err(&pdev->dev, "Failed to get GPIO: %ld\n", PTR_ERR(som_id->gpio[i]));
+      rc = PTR_ERR(som_id->gpio[i]);
+      goto error;
+    }
+  }
+
+  // make a sysfs entry for the SOM ID
+  rc = sysfs_create_group(&pdev->dev.kobj, &som_id_attr_group);
+  if (rc) {
+    dev_err(&pdev->dev, "Failed to create sysfs entry: %d\n", rc);
+    goto error;
+  }
+
+  platform_set_drvdata(pdev, som_id);
+error:
+	return rc;
+}
+
+static int gpio_som_id_remove(struct platform_device *pdev)
+{
+	struct gpio_som_id *som_id = dev_get_drvdata(&pdev->dev);
+
+  sysfs_remove_group(&pdev->dev.kobj, &som_id_attr_group);
+	return 0;
+}
+
+static const struct of_device_id of_match_table[] = {
+	{ .compatible = "comma,gpio-som-id", },
+	{}
+};
+
+static struct platform_driver gpio_som_id_driver = {
+	.driver		= {
+		.name	= "comma,gpio-som-id",
+		.of_match_table = of_match_table,
+	},
+	.probe		= gpio_som_id_probe,
+	.remove		= gpio_som_id_remove,
+};
+
+module_driver(gpio_som_id_driver, platform_driver_register, platform_driver_unregister);
+
+MODULE_DESCRIPTION("GPIO SOM ID driver");
+MODULE_LICENSE("MIT");