Re: [PATCH 3/5] hwmon: (pmbus/core) Add mapping function to pmbus_read_block_data()

On 7/30/26 08:19, Nuno Sá wrote:
> On Thu, Jul 30, 2026 at 07:47:37AM -0700, Guenter Roeck wrote:
>> On 7/30/26 07:27, Nuno Sá wrote:
>>> On Tue, Jul 28, 2026 at 02:05:53PM -0700, Guenter Roeck wrote:
>>>> On 7/28/26 09:03, Nuno Sá via B4 Relay wrote:
>>>>> From: Nuno Sá <[email protected]>
>>>>>
>>>>> This is in preparation for adding support to a device which needs to
>>>>> use it's own read_block implementation.
>>>>>
>>>>
>>>> The chip-specific implementation calls i2c_smbus_read_i2c_block_data().
>>>> I'll need to know if this is a chip limit or a controller limit.
>>>> If it is a controller limit, a chip specific override would be
>>>> inappropriate.
>>>
>>> I'll reply from top of my head (did not looked at the driver again).
>>> IIRC, the biggest reason we need the chip-specific implementation is because of
>>> the RAIL selection logic (mainly when not in page mode).
>>>
>>
>> Yes, I have seen that. Question is why you use i2c_smbus_read_i2c_block_data()
>> instead of i2c_smbus_read_block_data(). The rail selection logic would not
>> require that.
> 
> IIRC the reason was because the i2c controller on the raspberry pie does not
> support i2c_smbus_read_block_data(). So I guess this:
> 
> https://elixir.bootlin.com/linux/v7.1.4/source/drivers/i2c/i2c-core-smbus.c#L220
> 

Hmm, I think we really need a common solution for that problem. Not all
controllers support i2c_smbus_read_i2c_block_data(), so you are just moving
the problem from one controller to another.

One key example is the PIIX4 driver. Your new driver does not support the
majority of PC style systems with AMD CPUs.

Guenter