Re: [PATCH RFC] i2c: Use ID table to detect ACPI I2C devices

[Robert Dolca]

On Wed, May 20, 2015 at 10:47 AM, Mika Westerberg wrote:
> On Tue, May 19, 2015 at 05:03:29PM +0300, Robert Dolca wrote:
>> For i2c devices enumerated with ACPI you need to declare both
>> acpi_match_table and id_table. When using ACPI, the i2c_device_id structure
>> supplied to the probe function is null and you have to handle this case
>> in the driver.
>>
>> The current name for the i2c client when using ACPI is "HID:UID" where the
>> UID has 7 or 8 characters and the UID has 2 characters. The UID is not
>> relevant for identifying the chip so it does not have any practical
>> purpose.
>
> First of all, it is not "HID:UID" since the number after ":" is actually
> increasing number assigned by the ACPI core. Nothing to do with _UID.

You are right. My mistake.

> Secondly we do not list "_HID:nn" in drivers acpi_match_tables but
> instead it is either "HID" or "CID", no ":nn" there.

I didn't say that you do that :)

>
>> Modifying i2c_match_id we make the comparison by ignoring the UID from the
>> client name when the device was discovered using ACPI. The comparison is
>> case insensitive because the ACPI names are uppercase and the DT and ID
>> table names are lowercase. It would not make sense to have two different
>> chips with the same name and the only diference being the capitalized
>> letters.
>>
>> With these changes the probe function gets a valid i2c_device_id and the
>> driver doesn't have to declare acpi_match_table.
>
> No. We don't do that for DT and we definitely don't want to mix ACPI
> identifiers with arbitrary I2C device names.
>
> You are not supposed to put ACPI identifiers into i2c_device_id table.

Currently, if the name used for DT (in dts) matches one of the names
specified in the id table you will have a match. Isn't that an
intended behavior?

Robert
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/