[RFC PATCH 7/9] apple-gmux: add sysfs interface

[Orlando Chamberlain <orlandoch.dev@gmail.com>]

Allow reading gmux ports from userspace. When the unsafe module
parameter allow_user_writes is true, writing 1 byte
values is also allowed.

For example:

cd /sys/bus/acpi/devices/APP000B:00/physical_node/
echo 4 > gmux_selected_port
cat gmux_selected_port_data | xxd -p

Will show the gmux version information (00000005 in this case)

Signed-off-by: Orlando Chamberlain <orlandoch.dev@gmail.com>
---
 drivers/platform/x86/apple-gmux.c | 129 ++++++++++++++++++++++++++++++
 1 file changed, 129 insertions(+)

diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
index c38d6ef0c15a..756059d48393 100644
--- a/drivers/platform/x86/apple-gmux.c
+++ b/drivers/platform/x86/apple-gmux.c
@@ -66,6 +66,11 @@ struct apple_gmux_data {
 	enum vga_switcheroo_client_id switch_state_external;
 	enum vga_switcheroo_state power_state;
 	struct completion powerchange_done;
+
+#ifdef CONFIG_SYSFS
+	/* sysfs data */
+	int selected_port;
+#endif /* CONFIG_SYSFS */
 };
 
 static struct apple_gmux_data *apple_gmux_data;
@@ -651,6 +656,121 @@ static void gmux_notify_handler(acpi_handle device, u32 value, void *context)
 		complete(&gmux_data->powerchange_done);
 }
 
+/**
+ * DOC: Sysfs Interface
+ *
+ * gmux ports can be read from userspace as a sysfs interface. For example:
+ *
+ * # echo 4 > /sys/bus/acpi/devices/APP000B:00/physical_node/gmux_selected_port
+ * # cat /sys/bus/acpi/devices/APP000B:00/physical_node/gmux_selected_port_data | xxd -p
+ * 00000005
+ *
+ * Reads 4 bytes from port 4 (GMUX_PORT_VERSION_MAJOR).
+ *
+ * Single byte writes are also supported, however this must be enabled with the
+ * unsafe allow_user_writes module parameter.
+ *
+ */
+
+#ifdef CONFIG_SYSFS
+
+static bool allow_user_writes;
+module_param_unsafe(allow_user_writes, bool, 0);
+MODULE_PARM_DESC(allow_user_writes, "Allow userspace to write to gmux ports (default: false) (bool)");
+
+static ssize_t gmux_selected_port_store(struct device *dev,
+		struct device_attribute *attr, const char *sysfsbuf, size_t count)
+{
+	struct apple_gmux_data *gmux_data = dev_get_drvdata(dev);
+	u8 port;
+
+	if (kstrtou8(sysfsbuf, 10, &port) < 0)
+		return -EINVAL;
+
+	/* On pio gmux's, make sure the user doesn't access too high of a port. */
+	if ((gmux_data->config == &apple_gmux_pio) &&
+		port > (gmux_data->iolen - 4))
+		return -EINVAL;
+
+	gmux_data->selected_port = port;
+	return count;
+}
+
+static ssize_t gmux_selected_port_show(struct device *dev,
+		struct device_attribute *attr, char *sysfsbuf)
+{
+	struct apple_gmux_data *gmux_data = dev_get_drvdata(dev);
+
+	return sysfs_emit(sysfsbuf, "%d\n", gmux_data->selected_port);
+}
+
+DEVICE_ATTR_RW(gmux_selected_port);
+
+static ssize_t gmux_selected_port_data_store(struct device *dev,
+		struct device_attribute *attr, const char *sysfsbuf, size_t count)
+{
+	struct apple_gmux_data *gmux_data = dev_get_drvdata(dev);
+
+	if (count == 1)
+		gmux_write8(gmux_data, gmux_data->selected_port, *sysfsbuf);
+	else
+		return -EINVAL;
+
+	return count;
+}
+
+static ssize_t gmux_selected_port_data_show(struct device *dev,
+		struct device_attribute *attr, char *sysfsbuf)
+{
+	struct apple_gmux_data *gmux_data = dev_get_drvdata(dev);
+	u32 data;
+
+	data = gmux_read32(gmux_data, gmux_data->selected_port);
+	memcpy(sysfsbuf, &data, sizeof(data));
+
+	return sizeof(data);
+}
+
+struct device_attribute dev_attr_gmux_selected_port_data_rw = __ATTR_RW(gmux_selected_port_data);
+struct device_attribute dev_attr_gmux_selected_port_data_ro = __ATTR_RO(gmux_selected_port_data);
+
+static int gmux_init_sysfs(struct pnp_dev *pnp)
+{
+	int ret;
+
+	ret = device_create_file(&pnp->dev, &dev_attr_gmux_selected_port);
+	if (ret)
+		return ret;
+	if (allow_user_writes)
+		ret = device_create_file(&pnp->dev, &dev_attr_gmux_selected_port_data_rw);
+	else
+		ret = device_create_file(&pnp->dev, &dev_attr_gmux_selected_port_data_ro);
+	if (ret)
+		device_remove_file(&pnp->dev, &dev_attr_gmux_selected_port);
+	return ret;
+}
+
+static void gmux_fini_sysfs(struct pnp_dev *pnp)
+{
+	device_remove_file(&pnp->dev, &dev_attr_gmux_selected_port);
+	if (allow_user_writes)
+		device_remove_file(&pnp->dev, &dev_attr_gmux_selected_port_data_rw);
+	else
+		device_remove_file(&pnp->dev, &dev_attr_gmux_selected_port_data_ro);
+}
+
+#else
+
+static int gmux_init_sysfs(struct pnp_dev *pnp)
+{
+	return 0;
+}
+static void gmux_fini_sysfs(struct pnp_dev *pnp)
+{
+}
+
+#endif /* CONFIG_SYSFS */
+
 static int gmux_suspend(struct device *dev)
 {
 	struct pnp_dev *pnp = to_pnp_dev(dev);
@@ -846,8 +966,16 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
 		goto err_register_handler;
 	}
 
+	ret = gmux_init_sysfs(pnp);
+	if (ret) {
+		pr_err("Failed to register gmux sysfs entries\n");
+		goto err_sysfs;
+	}
+
 	return 0;
 
+err_sysfs:
+	vga_switcheroo_unregister_handler();
 err_register_handler:
 	gmux_disable_interrupts(gmux_data);
 	apple_gmux_data = NULL;
@@ -877,6 +1005,7 @@ static void gmux_remove(struct pnp_dev *pnp)
 {
 	struct apple_gmux_data *gmux_data = pnp_get_drvdata(pnp);
 
+	gmux_fini_sysfs(pnp);
 	vga_switcheroo_unregister_handler();
 	gmux_disable_interrupts(gmux_data);
 	if (gmux_data->gpe >= 0) {
-- 
2.39.1