Re: [PATCH 2/2] hwmon: (pmbus/max20830) add driver for max20830

On 4/15/26 20:04, Torreno, Alexis Czezar wrote:
>>>
>>> I may need to keep i2c_smbus_read_i2c_block_data. I'm testing this on
>>> an rpi4 and it seems i2c_smbus_read_block_data isn't supported by the
>> adapter.
>>>
>>
>> Odd. I can see that the bcm2835 controller driver sets
>> I2C_FUNC_SMBUS_EMUL but not I2C_FUNC_SMBUS_BLOCK_DATA. That
>> makes me wonder if the controller really does not support block reads. Any
>> chance you can try setting that flag in ./drivers/i2c/busses/i2c-bcm2835.c and
>> see what happens ?
>>
> 
> I tried using i2c_smbus_read_block_data, and here's some log messages
> 
> [ 6857.261998] max20830: adapter does NOT support I2C_FUNC_SMBUS_BLOCK_DATA
> [ 6857.262006] max20830: adapter supports I2C_FUNC_SMBUS_READ_I2C_BLOCK
> [ 6857.265228] max20830: i2c_block_data read 32 bytes: '        MAX20830'
> [ 6857.265648] max20830: smbus_block_data read 9 bytes: ''
> 
> i2c_smbus_read_i2c_block_data returns 32 for 32 bytes read
> and the buffer content is expected "MAX20830"
> 
> i2c_smbus_read_block_data returned 9 so I think it read the payload length of 1byte
> but no data beyond it, hence buffer = ''
> 

Ok, worth a try. The "correct" fix would be to implement support for the command
in the I2C controller driver, but that would be too much to ask for.

Ok to use i2c_smbus_read_i2c_block_data, but please add a comment describing
the reason, i.e., that this is to support drivers/controllers which don't support
i2c_smbus_read_block_data(). Also, please implement code to address the
differences: The first returned byte is the real length, so please check that.
Also, please fix the "Unsupported device" log to not print the first byte.

Thanks,
Guenter