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

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Message-ID: <CAFPB+YcggLY9vwtYREX_YVVJFrTYHTQYnBtvMcicvLgo5MX-+A@mail.gmail.com>
Date:	Wed, 20 May 2015 13:49:02 +0300
From:	Robert Dolca <robert.dolca@...il.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Robert Dolca <robert.dolca@...el.com>, linux-i2c@...r.kernel.org,
	linux-acpi@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	Daniel Baluta <daniel.baluta@...el.com>
Subject: Re: [PATCH RFC] i2c: Use ID table to detect ACPI I2C devices

On Wed, May 20, 2015 at 12:48 PM, Mika Westerberg wrote:
> On Wed, May 20, 2015 at 12:39:22PM +0300, Robert Dolca wrote:
>> 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?
>
> I thought one needs to put IDs to the driver .of_match_table. This is
> also what i2c_device_match() is expecting, if I read it right.

If you put the DT id in of_match_table it will match here:

i2c_device_match
        /* Attempt an OF style match */
        if (of_driver_match_device(dev, drv))
                return 1;

If you don't specify of_match_table and you put the same ID in
i2c_device_id table it wil match here:

i2c_device_match
        driver = to_i2c_driver(drv);
        /* match on an id table if there is one */
        if (driver->id_table)
                return i2c_match_id(driver->id_table, client) != NULL;

This is happening because the name from dts is used for client->name.
i2c_match_id does the matching based on the client name.

> BTW, how modules are supposed to be matched if we allow putting ACPI
> identifiers to i2c_device_id table?

My aproach was like this: if the driver specifies .acpi_match table it
will work like before.

i2c_device_match
        /* Then ACPI style match */
        if (acpi_driver_match_device(dev, drv))
                return 1;

If the driver does not specify .acpi_match table the i2c core will
atempt to match against the  i2c_match_id table (the same way it does
for DT). In the ACPI case the client->name has that :nn suffix and
what the patch does is to ignore that when i2c_match_id is called.

i2c_device_match
        driver = to_i2c_driver(drv);
        /* match on an id table if there is one */
        if (driver->id_table)
                return i2c_match_id(driver->id_table, client) != NULL;

The final goal is to simplify the driver and remove redundant code.

Robert
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