Re: [PATCH v4 6/6] platform/x86: dell-smo8800: Add support for probing for the accelerometer i2c address

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

Hi Pali,

On 6/24/24 8:21 PM, Pali Rohár wrote:
> On Monday 24 June 2024 13:15:18 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>
> 
> My comments from the previous version still apply there. There is no
> dangerous warning neither in parameter name and its description, there
> is no warning once the parameter was specified.

I have added the same "this may be dangerous" text from:

  pr_info("Pass dell_lis3lv02d.probe_i2c_addr=1 on the kernel commandline to probe, this may be dangerous!\n");

to the MODULE_PARM_DESC() now too (for v5).

> And there is missing
> information from Dell how it is going to be handled for new
> machines. So first ask Dell about the current state and future.

As mentioned before Dell is on the Cc. And I no longer have any direct
contacts inside Dell. If you know anyone inside Dell feel free to email
them about this.

Regards,

Hans



>> ---
>>  drivers/platform/x86/dell/dell-lis3lv02d.c | 133 ++++++++++++++++++++-
>>  1 file changed, 131 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/platform/x86/dell/dell-lis3lv02d.c b/drivers/platform/x86/dell/dell-lis3lv02d.c
>> index a7409db0505b..173615fd2646 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 const struct dmi_system_id *lis3lv02d_dmi_id;
>>  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 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 = (long)lis3lv02d_dmi_id->driver_data;
>> +	if (lis3lv02d_dmi_id) {
>> +		info.addr = (long)lis3lv02d_dmi_id->driver_data;
>> +	} 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);
>> @@ -166,8 +294,9 @@ 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;
>>  	}
>>  
>> -- 
>> 2.45.1
>>
>