[PATCH v2 5/6] platform/x86: dell-smo8800: Add support for probing for the accelerometer i2c address

Hans de Goede
2024-01-06T16:09:58Z

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 | 112 +++++++++++++++++++++--
1 file changed, 105 insertions(+), 7 deletions(-)

diff --git a/drivers/platform/x86/dell/dell-smo8800.c b/drivers/platform/x86/dell/dell-smo8800.c
index 58bb7275ba5c..021ad31eb84d 100644
--- a/drivers/platform/x86/dell/dell-smo8800.c
+++ b/drivers/platform/x86/dell/dell-smo8800.c
@@ -29,6 +29,10 @@ static bool use_iio_driver;
module_param(use_iio_driver, bool, 0444);
MODULE_PARM_DESC(use_iio_driver, "Use IIO accelerometer driver instead of /dev/freefall chardev + evdev joystick emulation");

+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 */
@@ -150,6 +154,82 @@ static int smo8800_find_i801(struct device *dev, void *data)
return 1;
}

+/*
+ * 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 smo8800_device *smo8800, 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(smo8800->dev, "I2C safety check for address 0x%02x failed, skipping\n", addr);
+ return -ENODEV;
+}
+
/*
* Set label to let iio-sensor-proxy know these freefall sensors are located in
* the laptop base (not the display) and are not intended for screen rotation.
@@ -165,12 +245,19 @@ const struct software_node smo8800_accel_node = {

static int smo8800_detect_accel(struct smo8800_device *smo8800,
struct i2c_adapter *adap, u8 addr,
- struct i2c_board_info *info)
+ 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, 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) {
@@ -256,17 +343,25 @@ static void smo8800_instantiate_i2c_client(struct smo8800_device *smo8800)
}
}

- if (!addr) {
+ if (addr) {
+ /* Always detect the accel-type, this also checks the accel is actually there */
+ err = smo8800_detect_accel(smo8800, adap, addr, &info, false);
+ if (err)
+ goto 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, "No accelerometer found\n");
+ goto put_adapter;
+ }
+ } else {
dev_warn(smo8800->dev,
"Accelerometer lis3lv02d is present on SMBus but its address is unknown, skipping registration\n");
+ dev_info(smo8800->dev, "Pass dell_smo8800.probe_i2c_addr=1 on the kernel commandline to probe, this may be dangerous!\n");
goto put_adapter;
}

- /* Always detect the accel-type, this also checks the accel is actually there */
- err = smo8800_detect_accel(smo8800, adap, addr, &info);
- if (err)
- goto put_adapter;
-
/*
* Unless using the IIO driver is requested, override the detected type
* with "lis3lv02d" so that drivers/misc/lis3lv02d/lis3lv02d.c is used
@@ -285,6 +380,9 @@ static void smo8800_instantiate_i2c_client(struct smo8800_device *smo8800)
} else {
dev_info(smo8800->dev, "Registered %s accelerometer on address 0x%02x\n",
info.type, info.addr);
+ if (!addr)
+ dev_info(smo8800->dev,
+ "Please report this address upstream together with the output of 'cat /sys/class/dmi/id/product_name'\n");
}
put_adapter:
i2c_put_adapter(adap);
--
2.43.0