[RFC PATCH 14/14] mfd/macsmc: add ioctl to access smc keys

[Atharva Tiwari <atharvatiwarilinuxdev@gmail.com>]

Add a /dev/smc device so userspace can talk to the SMC
directly. Some keys that need to be written aren't handled by
any driver, or affect several drivers at once, so they
can't be exposed cleanly through the kernel interfaces.

Keys already managed by kernel drivers can't be written this
way, to avoid conflicts.

Signed-off-by: Atharva Tiwari <atharvatiwarilinuxdev@gmail.com>
---
 drivers/mfd/macsmc-core.c  | 155 +++++++++++++++++++++++++++++++++++++
 include/linux/mfd/macsmc.h |  27 +++++++
 2 files changed, 182 insertions(+)

diff --git a/drivers/mfd/macsmc-core.c b/drivers/mfd/macsmc-core.c
index bc4200f57..a30f7386e 100644
--- a/drivers/mfd/macsmc-core.c
+++ b/drivers/mfd/macsmc-core.c
@@ -6,10 +6,13 @@
 
 #include <linux/bitfield.h>
 #include <linux/device.h>
+#include <linux/fs.h>
 #include <linux/mfd/core.h>
 #include <linux/mfd/macsmc.h>
+#include <linux/miscdevice.h>
 #include <linux/mutex.h>
 #include <linux/spinlock.h>
+#include <linux/uaccess.h>
 
 static const struct mfd_cell apple_smc_rtkit_devs[] = {
 	MFD_CELL_NAME("macsmc-input"),
@@ -112,6 +115,144 @@ static void apple_smc_disable_notifications(void *data)
 	smc->be->disable_notifications(smc->be_cookie);
 }
 
+static long apple_smc_fops_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	struct apple_smc *smc = file->private_data;
+	void __user *argp = (void __user *)arg;
+	int ret;
+
+	switch (cmd) {
+	case IOCTL_SMC_READ: {
+		struct ioctl_smc_rw_payload payload;
+		struct apple_smc_key_info info;
+
+		if (copy_from_user(&payload, argp, sizeof(payload)))
+			return -EFAULT;
+
+		ret = apple_smc_get_key_info(smc, payload.key, &info);
+		if (ret < 0)
+			return ret;
+
+		if (payload.size != info.size)
+			return -EINVAL;
+
+		if (payload.size > 32)
+			return -EINVAL;
+
+		ret = apple_smc_read(smc, payload.key, payload.buf, payload.size);
+		if (ret < 0)
+			return ret;
+
+		if (copy_to_user(argp, &payload, sizeof(payload)))
+			return -EFAULT;
+		return 0;
+	}
+	case IOCTL_SMC_WRITE: {
+		struct ioctl_smc_rw_payload payload;
+		struct apple_smc_key_info info;
+
+		if (copy_from_user(&payload, argp, sizeof(payload)))
+			return -EFAULT;
+
+		ret = apple_smc_get_key_info(smc, payload.key, &info);
+		if (ret < 0)
+			return ret;
+
+		if (payload.size != info.size)
+			return -EINVAL;
+
+		if (payload.size > 32)
+			return -EINVAL;
+
+		switch (payload.key) {
+		case __SMC_KEY('C', 'H', '0', 'I'):
+		case __SMC_KEY('C', 'H', '0', 'C'):
+		case __SMC_KEY('C', 'H', '0', 'K'):
+		case __SMC_KEY('C', 'H', '0', 'B'):
+		case __SMC_KEY('C', 'H', 'T', 'E'):
+		case __SMC_KEY('C', 'H', 'L', 'S'):
+		case __SMC_KEY('B', 'C', 'L', 'M'):
+		case __SMC_KEY('M', 'B', 'S', 'E'):
+		case __SMC_KEY('C', 'L', 'K', 'L'):
+		case __SMC_KEY('C', 'L', 'K', 'O'):
+		case __SMC_KEY('O', 'S', 'W', 'D'):
+		case __SMC_KEY('N', 'A', 'T', 'J'):
+		case __SMC_KEY('N', 'A', 'T', 'i'):
+		case __SMC_KEY('N', 'E', 'S', 'N'):
+		case __SMC_KEY('M', 'O', 'C', 'N'):
+		case __SMC_KEY('L', 'K', 'S', 'B'):
+		case __SMC_KEY('N', 'T', 'O', 'K'):
+		case __SMC_KEY('N', 'T', 'A', 'P'):
+		case __SMC_KEY('F', '0', 'T', 'g'):
+		case __SMC_KEY('F', '1', 'T', 'g'):
+		case __SMC_KEY('F', '0', 'M', 'd'):
+		case __SMC_KEY('F', '1', 'M', 'd'):
+		case __SMC_KEY('F', 'S', '!', ' '):
+			return -EPERM;
+		}
+
+		ret = apple_smc_write(smc, payload.key, payload.buf, payload.size);
+		if (ret < 0)
+			return ret;
+
+		return 0;
+	}
+	case IOCTL_SMC_GET_KEY_INDEX: {
+		struct ioctl_smc_index_payload payload;
+
+		if (copy_from_user(&payload, argp, sizeof(payload)))
+			return -EFAULT;
+
+		ret = apple_smc_get_key_by_index(smc, payload.index, &payload.key);
+		if (ret < 0)
+			return ret;
+
+		if (copy_to_user(argp, &payload, sizeof(payload)))
+			return -EFAULT;
+
+		return 0;
+	}
+	case IOCTL_SMC_GET_KEY_INFO: {
+		struct ioctl_smc_info_payload payload;
+
+		if (copy_from_user(&payload, argp, sizeof(payload)))
+			return -EFAULT;
+
+		ret = apple_smc_get_key_info(smc, payload.key, &payload.info);
+		if (ret < 0)
+			return ret;
+
+		if (copy_to_user(argp, &payload, sizeof(payload)))
+			return -EFAULT;
+
+		return 0;
+	}
+	default:
+		return -EINVAL;
+	}
+}
+
+static int apple_smc_fops_open(struct inode *inode, struct file *file)
+{
+	struct miscdevice *misc = file->private_data;
+
+	file->private_data = container_of(misc, struct apple_smc, miscdev);
+	return 0;
+}
+
+static const struct file_operations apple_smc_fops = {
+	.owner		= THIS_MODULE,
+	.open		= apple_smc_fops_open,
+	.unlocked_ioctl	= apple_smc_fops_ioctl,
+	.compat_ioctl	= compat_ptr_ioctl,
+	.llseek		= noop_llseek,
+};
+
+static void apple_smc_misc_unregister(void *data)
+{
+	misc_deregister(data);
+}
+
 int apple_smc_probe(struct device *dev, const struct apple_smc_backend_ops *ops,
 		void *cookie, struct blocking_notifier_head *event_handlers, bool is_acpi)
 {
@@ -150,6 +291,20 @@ int apple_smc_probe(struct device *dev, const struct apple_smc_backend_ops *ops,
 	if (ret)
 		return ret;
 
+	smc->miscdev.minor = MISC_DYNAMIC_MINOR;
+	smc->miscdev.name = "smc";
+	smc->miscdev.fops = &apple_smc_fops;
+	smc->miscdev.parent = dev;
+	smc->miscdev.mode = 0600;
+
+	ret = misc_register(&smc->miscdev);
+	if (ret)
+		return ret;
+
+	ret = devm_add_action_or_reset(dev, apple_smc_misc_unregister, &smc->miscdev);
+	if (ret)
+		return ret;
+
 	if (smc->is_acpi) {
 		ret = devm_mfd_add_devices(dev, -1, apple_smc_acpi_common,
 			ARRAY_SIZE(apple_smc_acpi_common), NULL, 0, NULL);
diff --git a/include/linux/mfd/macsmc.h b/include/linux/mfd/macsmc.h
index 4b4368b99..29fd7b20c 100644
--- a/include/linux/mfd/macsmc.h
+++ b/include/linux/mfd/macsmc.h
@@ -8,6 +8,8 @@
 #ifndef _LINUX_MFD_MACSMC_H
 #define _LINUX_MFD_MACSMC_H
 
+#include <linux/ioctl.h>
+#include <linux/miscdevice.h>
 #include <linux/soc/apple/rtkit.h>
 
 /**
@@ -125,6 +127,7 @@ struct apple_smc_backend_ops {
  * @is_acpi: Is the backend ACPI based
  * @mutex: Mutex for non-atomic mode
  * @lock: Spinlock for atomic mode
+ * @miscdev: Misc Device struct for ioctl ops
  */
 struct apple_smc {
 	struct device *dev;
@@ -141,8 +144,32 @@ struct apple_smc {
 
 	struct mutex mutex;
 	spinlock_t lock;
+
+	struct miscdevice miscdev;
+};
+
+struct ioctl_smc_rw_payload {
+	smc_key key;
+	size_t size;
+	u8 buf[32];
+};
+
+struct ioctl_smc_index_payload {
+	int index;
+	smc_key key;
+};
+
+struct ioctl_smc_info_payload {
+	smc_key key;
+	struct apple_smc_key_info info;
 };
 
+#define APPLE_SMC_MAGIC 'S'
+#define IOCTL_SMC_READ           _IOWR(APPLE_SMC_MAGIC, 1, struct ioctl_smc_rw_payload)
+#define IOCTL_SMC_WRITE          _IOW(APPLE_SMC_MAGIC, 2, struct ioctl_smc_rw_payload)
+#define IOCTL_SMC_GET_KEY_INDEX  _IOWR(APPLE_SMC_MAGIC, 3, struct ioctl_smc_index_payload)
+#define IOCTL_SMC_GET_KEY_INFO   _IOWR(APPLE_SMC_MAGIC, 4, struct ioctl_smc_info_payload)
+
 /**
  * apple_smc_read - Read size bytes from given SMC key into buf
  * @smc: Pointer to apple_smc struct
-- 
2.55.0