[PATCH v3 6/6] platform/x86: dell-smo8800: Add support for probing for the accelerometer i2c address

[Hans de Goede <hdegoede@redhat.com>]

Unfortunately the SMOxxxx ACPI device does not contain the i2c-address
of the accelerometer. So a DMI product-name to address mapping table
is used.

At support to have the kernel probe for the i2c-address for modesl
which are not on the list.

The new probing code sits behind a new probe_i2c_addr module parameter,
which is disabled by default because probing might be dangerous.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/platform/x86/dell/dell-smo8800.c | 152 ++++++++++++++++++++++-
 1 file changed, 147 insertions(+), 5 deletions(-)

diff --git a/drivers/platform/x86/dell/dell-smo8800.c b/drivers/platform/x86/dell/dell-smo8800.c
index 4c79b2599d96..d64d200e927a 100644
--- a/drivers/platform/x86/dell/dell-smo8800.c
+++ b/drivers/platform/x86/dell/dell-smo8800.c
@@ -10,6 +10,7 @@
  */
 
 #define DRIVER_NAME "smo8800"
+#define LIS3_WHO_AM_I 0x0f
 
 #include <linux/device/bus.h>
 #include <linux/dmi.h>
@@ -25,6 +26,10 @@
 #include <linux/uaccess.h>
 #include <linux/workqueue.h>
 
+static bool probe_i2c_addr;
+module_param(probe_i2c_addr, bool, 0444);
+MODULE_PARM_DESC(probe_i2c_addr, "Probe the i801 I2C bus for the accelerometer on models where the address is unknown");
+
 struct smo8800_device {
 	u32 irq;                     /* acpi device irq */
 	atomic_t counter;            /* count after last read */
@@ -225,6 +230,130 @@ static const struct dmi_system_id smo8800_lis3lv02d_devices[] = {
 	{ }
 };
 
+/*
+ * This is the kernel version of the single register device sanity checks from
+ * the i2c_safety_check function from lm_sensors sensor-detect script:
+ * This is meant to prevent access to 1-register-only devices,
+ * which are designed to be accessed with SMBus receive byte and SMBus send
+ * byte transactions (i.e. short reads and short writes) and treat SMBus
+ * read byte as a real write followed by a read. The device detection
+ * routines would write random values to the chip with possibly very nasty
+ * results for the hardware. Note that this function won't catch all such
+ * chips, as it assumes that reads and writes relate to the same register,
+ * but that's the best we can do.
+ */
+static int i2c_safety_check(struct device *dev, struct i2c_adapter *adap, u8 addr)
+{
+	union i2c_smbus_data smbus_data;
+	int err;
+	u8 data;
+
+	/*
+	 * First receive a byte from the chip, and remember it. This
+	 * also checks if there is a device at the address at all.
+	 */
+	err = i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_READ, 0,
+			     I2C_SMBUS_BYTE, &smbus_data);
+	if (err < 0)
+		return err;
+
+	data = smbus_data.byte;
+
+	/*
+	 * Receive a byte again; very likely to be the same for
+	 * 1-register-only devices.
+	 */
+	err = i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_READ, 0,
+			     I2C_SMBUS_BYTE, &smbus_data);
+	if (err < 0)
+		return err;
+
+	if (smbus_data.byte != data)
+		return 0; /* Not a 1-register-only device. */
+
+	/*
+	 * Then try a standard byte read, with a register offset equal to
+	 * the read byte; for 1-register-only device this should read
+	 * the same byte value in return.
+	 */
+	err = i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_READ, data,
+			     I2C_SMBUS_BYTE_DATA, &smbus_data);
+	if (err < 0)
+		return err;
+
+	if (smbus_data.byte != data)
+		return 0; /* Not a 1-register-only device. */
+
+	/*
+	 * Then try a standard byte read, with a slightly different register
+	 * offset; this should again read the register offset in return.
+	 */
+	err = i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_READ, data ^ 0x01,
+			     I2C_SMBUS_BYTE_DATA, &smbus_data);
+	if (err < 0)
+		return err;
+
+	if (smbus_data.byte != (data ^ 0x01))
+		return 0; /* Not a 1-register-only device. */
+
+	/*
+	 * Apparently this is a 1-register-only device, restore the original
+	 * register value and leave it alone.
+	 */
+	i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_WRITE, data,
+		       I2C_SMBUS_BYTE, NULL);
+	dev_warn(dev, "I2C safety check for address 0x%02x failed, skipping\n", addr);
+	return -ENODEV;
+}
+
+static int smo8800_detect_accel(struct smo8800_device *smo8800,
+				struct i2c_adapter *adap, u8 addr,
+				struct i2c_board_info *info, bool probe)
+{
+	union i2c_smbus_data smbus_data;
+	const char *type;
+	int err;
+
+	if (probe) {
+		dev_info(smo8800->dev, "Probing for accelerometer on address 0x%02x\n", addr);
+		err = i2c_safety_check(smo8800->dev, adap, addr);
+		if (err < 0)
+			return err;
+	}
+
+	err = i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_READ, LIS3_WHO_AM_I,
+			     I2C_SMBUS_BYTE_DATA, &smbus_data);
+	if (err < 0) {
+		dev_warn(smo8800->dev, "Failed to read who-am-i register: %d\n", err);
+		return err;
+	}
+
+	/* who-am-i register mappings from drivers/misc/lis3lv02d/lis3lv02d.c */
+	switch (smbus_data.byte) {
+	case 0x32:
+		type = "lis331dlh";
+		break;
+	case 0x33:
+		type = "lis2de12"; /* LIS3DC / HP3DC in drivers/misc/lis3lv02d/lis3lv02d.c */
+		break;
+	case 0x3a:
+		type = "lis3lv02dl_accel";
+		break;
+	case 0x3b:
+		type = "lis302dl";
+		break;
+	default:
+		dev_warn(smo8800->dev, "Unknown who-am-i register value 0x%02x\n",
+			 smbus_data.byte);
+		return -ENODEV;
+	}
+
+	dev_dbg(smo8800->dev, "Detected %s accelerometer on address 0x%02x\n", type, addr);
+	strscpy(info->type, "lis3lv02d", I2C_NAME_SIZE);
+	info->addr = addr;
+	return 0;
+}
+
 static int smo8800_find_i801(struct device *dev, void *data)
 {
 	struct i2c_adapter *adap, **adap_ret = data;
@@ -247,6 +376,7 @@ static void smo8800_instantiate_i2c_client(struct work_struct *work)
 	const struct dmi_system_id *lis3lv02d_dmi_id;
 	struct i2c_board_info info = { };
 	struct i2c_adapter *adap = NULL;
+	int err;
 
 	if (smo8800->i2c_dev)
 		return;
@@ -256,11 +386,22 @@ static void smo8800_instantiate_i2c_client(struct work_struct *work)
 		return;
 
 	lis3lv02d_dmi_id = dmi_first_match(smo8800_lis3lv02d_devices);
-	if (!lis3lv02d_dmi_id)
+	if (lis3lv02d_dmi_id) {
+		info.addr = (long)lis3lv02d_dmi_id->driver_data;
+		/* Always detect the accel-type, this also checks the accel is actually there */
+		err = smo8800_detect_accel(smo8800, adap, info.addr, &info, false);
+		if (err)
+			goto out_put_adapter;
+	} else if (probe_i2c_addr) {
+		/* First try address 0x29 (most used) and then try 0x1d */
+		if (smo8800_detect_accel(smo8800, adap, 0x29, &info, true) != 0 &&
+		    smo8800_detect_accel(smo8800, adap, 0x1d, &info, true) != 0) {
+			dev_warn(smo8800->dev, "failed to probe for lis3lv02d I2C address\n");
+			goto out_put_adapter;
+		}
+	} else {
 		goto out_put_adapter;
-
-	info.addr = (long)lis3lv02d_dmi_id->driver_data;
-	strscpy(info.type, "lis3lv02d", I2C_NAME_SIZE);
+	}
 
 	smo8800->i2c_dev = i2c_new_client_device(adap, &info);
 	if (IS_ERR(smo8800->i2c_dev)) {
@@ -357,7 +498,7 @@ static int smo8800_probe(struct platform_device *device)
 			 smo8800->irq);
 	}
 
-	if (dmi_check_system(smo8800_lis3lv02d_devices)) {
+	if (dmi_check_system(smo8800_lis3lv02d_devices) || probe_i2c_addr) {
 		/*
 		 * Register i2c-bus notifier + queue initial scan for lis3lv02d
 		 * i2c_client instantiation.
@@ -370,6 +511,7 @@ static int smo8800_probe(struct platform_device *device)
 	} else {
 		dev_warn(&device->dev,
 			 "lis3lv02d accelerometer is present on SMBus but its address is unknown, skipping registration\n");
+		dev_info(&device->dev, "Pass dell_smo8800.probe_i2c_addr=1 on the kernel commandline to probe, this may be dangerous!\n");
 		if (!smo8800->irq)
 			return -ENODEV;
 	}
-- 
2.45.1