Re: [PATCH] at24: add SMBus fallback for adapters lacking I2C_FUNC_I2C

[Mark Brown]

On Tue, Apr 07, 2026 at 12:54:49PM +0200, Bartosz Golaszewski wrote:
> On Sat, Apr 4, 2026 at 4:19 AM Nishanth Sampath Kumar

> > 1. AT24_FLAG_ADDR16 EEPROMs (e.g. 24c64 syseeprom):
> >    regmap_get_i2c_bus() returns -ENOTSUPP (-524) for reg_bits=16
> >    because neither I2C_FUNC_I2C nor I2C_FUNC_SMBUS_I2C_BLOCK is set.
> >    The driver probe fails entirely with:
> >      at24 3-0055: probe with driver at24 failed with error -524

If you can implement a fallback for whatever configuration this device
has then you should just implement that in the regmap core.

> > 2. 8-bit addressed EEPROMs (e.g. 24c02 fan EEPROMs) behind a pca9548
> >    mux on a PIIX4 child adapter: regmap selects regmap_i2c_smbus_i2c_block
> >    which fails at runtime even though SMBUS_BYTE_DATA is available.

If the device is advertising capabilities that it does not actually
support then the capability advertisment should be fixed.

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