Re: [PATCH v5 6/6] platform/x86: dell-smo8800: Add support for probing for the accelerometer i2c address

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

Hi All,

On 7/3/24 1:05 PM, Hans de Goede wrote:
> 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.
> 
> Link: https://lore.kernel.org/linux-i2c/4820e280-9ca4-4d97-9d21-059626161bfc@molgen.mpg.de/
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>

The discussion about i2c probing in the v4 patch-ser thread made me look
at how the i2c-core handles the probing now a days and it now actually
has a helper to do exactly what this patch is doing, scan a couple of
addresses and instantiate an i2c_client on the first address where
the device is found: i2c_new_scanned_device().

So I plan to do a v6 of the series, updating this patch to use this
helper instead of using DIY code.

Regards,

Hans



> ---
>  drivers/platform/x86/dell/dell-lis3lv02d.c | 136 ++++++++++++++++++++-
>  1 file changed, 133 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/platform/x86/dell/dell-lis3lv02d.c b/drivers/platform/x86/dell/dell-lis3lv02d.c
> index ab02ad93758a..5e4b24ec02f1 100644
> --- a/drivers/platform/x86/dell/dell-lis3lv02d.c
> +++ b/drivers/platform/x86/dell/dell-lis3lv02d.c
> @@ -15,6 +15,8 @@
>  #include <linux/workqueue.h>
>  #include "dell-smo8800-ids.h"
>  
> +#define LIS3_WHO_AM_I 0x0f
> +
>  #define DELL_LIS3LV02D_DMI_ENTRY(product_name, i2c_addr)                 \
>  	{                                                                \
>  		.matches = {                                             \
> @@ -57,6 +59,121 @@ static u8 i2c_addr;
>  static struct i2c_client *i2c_dev;
>  static bool notifier_registered;
>  
> +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, this may be dangerous.");
> +
> +/*
> + * 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 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);
> +	pr_warn("I2C safety check for address 0x%02x failed, skipping\n", addr);
> +	return -ENODEV;
> +}
> +
> +static int detect_lis3lv02d(struct i2c_adapter *adap, u8 addr,
> +			    struct i2c_board_info *info)
> +{
> +	union i2c_smbus_data smbus_data;
> +	int err;
> +
> +	pr_info("Probing for lis3lv02d on address 0x%02x\n", addr);
> +	err = i2c_safety_check(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) {
> +		pr_warn("Failed to read who-am-i register: %d\n", err);
> +		return err;
> +	}
> +
> +	/* valid who-am-i values are from drivers/misc/lis3lv02d/lis3lv02d.c */
> +	switch (smbus_data.byte) {
> +	case 0x32:
> +	case 0x33:
> +	case 0x3a:
> +	case 0x3b:
> +		break;
> +	default:
> +		pr_warn("Unknown who-am-i register value 0x%02x\n", smbus_data.byte);
> +		return -ENODEV;
> +	}
> +
> +	pr_debug("Detected lis3lv02d on address 0x%02x\n", addr);
> +	info->addr = addr;
> +	return 0;
> +}
> +
>  static bool i2c_adapter_is_main_i801(struct i2c_adapter *adap)
>  {
>  	/*
> @@ -93,7 +210,17 @@ static void instantiate_i2c_client(struct work_struct *work)
>  	if (!adap)
>  		return;
>  
> -	info.addr = i2c_addr;
> +	if (i2c_addr) {
> +		info.addr = i2c_addr;
> +	} else {
> +		/* First try address 0x29 (most used) and then try 0x1d */
> +		if (detect_lis3lv02d(adap, 0x29, &info) != 0 &&
> +		    detect_lis3lv02d(adap, 0x1d, &info) != 0) {
> +			pr_warn("failed to probe for lis3lv02d I2C address\n");
> +			goto out_put_adapter;
> +		}
> +	}
> +
>  	strscpy(info.type, "lis3lv02d", I2C_NAME_SIZE);
>  
>  	i2c_dev = i2c_new_client_device(adap, &info);
> @@ -104,6 +231,7 @@ static void instantiate_i2c_client(struct work_struct *work)
>  		pr_debug("registered lis3lv02d on address 0x%02x\n", info.addr);
>  	}
>  
> +out_put_adapter:
>  	i2c_put_adapter(adap);
>  }
>  static DECLARE_WORK(i2c_work, instantiate_i2c_client);
> @@ -167,12 +295,14 @@ static int __init dell_lis3lv02d_init(void)
>  	put_device(dev);
>  
>  	lis3lv02d_dmi_id = dmi_first_match(lis3lv02d_devices);
> -	if (!lis3lv02d_dmi_id) {
> +	if (!lis3lv02d_dmi_id && !probe_i2c_addr) {
>  		pr_warn("accelerometer is present on SMBus but its address is unknown, skipping registration\n");
> +		pr_info("Pass dell_lis3lv02d.probe_i2c_addr=1 on the kernel commandline to probe, this may be dangerous!\n");
>  		return 0;
>  	}
>  
> -	i2c_addr = (long)lis3lv02d_dmi_id->driver_data;
> +	if (lis3lv02d_dmi_id)
> +		i2c_addr = (long)lis3lv02d_dmi_id->driver_data;
>  
>  	/*
>  	 * Register i2c-bus notifier + queue initial scan for lis3lv02d