From mboxrd@z Thu Jan  1 00:00:00 1970
From: Lars-Peter Clausen <lars@metafoo.de>
Subject: Re: SSM2518 Device Tree support ?
Date: Tue, 01 Sep 2015 09:51:50 +0200
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To: Ricard Wanderlof <ricard.wanderlof@axis.com>
Cc: "alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>
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On 09/01/2015 09:06 AM, Ricard Wanderlof wrote:
> 
> Bringing up an old thread becuase i have a similar issue with the 
> adau1761-i2c.c driver which should be configurable in the same way - it 
> links into the I2C driver framework too. I know my ssm2518.c patch was 
> recently applied, but using this driver (prior to the patch) as an 
> example as Lars-Peter mentioned that it should be able to work this way.
> 
> On Thu, 13 Aug 2015, Lars-Peter Clausen wrote:
> 
>> [ ... device tree support in ssm2518.c ... ]
>> What's not in the driver is a explicit of match table. It will work without
>> since the I2C subsystem supports matching based on the I2C ID table.
> 
> How does this actually work? I've tried to figure it out but haven't 
> gotten anywhere.
> 
> From:
> 
> http://wiki.analog.com/resources/tools-software/linux-drivers/sound/ssm2518 :
> 
> 
> i2s: i2c@41600000 {
> 	compatible = "...;
> 	...
> 
> 	#size-cells = <0>;
> 	#address-cells = <1>;
>             
> 	ssm2518: ssm2518@34 {
> 		compatible = "adi,ssm2518";
> 		reg = <0x34>;
> 		gpios = <&gpio 5 0>;
> 	};
> };
> 
> 
> In codecs/ssm2518.c:
> 
> 
> static const struct i2c_device_id ssm2518_i2c_ids[] = {
>         { "ssm2518", 0 },
>         { }
> };
> MODULE_DEVICE_TABLE(i2c, ssm2518_i2c_ids);
> 
> static struct i2c_driver ssm2518_driver = {
>         .driver = {
>                 .name = "ssm2518",
>                 .owner = THIS_MODULE,
>         },
>         .probe = ssm2518_i2c_probe,
>         .remove = ssm2518_i2c_remove,
>         .id_table = ssm2518_i2c_ids,
> };
> module_i2c_driver(ssm2518_driver);
> 
> 
> So how does the i2c framework ultimately get the ssm2518 probe function to 
> be called? The only real ID here are the strings "ssm2518" but they don't 
> show up in the DT entry, except as part of the ssm2518 compatible string.

It splits the compatible string at the comma and then looks for a driver
that matches the later part. Have a look at of_modalias_node().

- Lars