two kernel modules for the same device address in dts

two kernel modules for the same device address in dts

[Tomek The Messenger]

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Hi
I am trying to design some functionality and I wonder if something like
that is supported in dts and linux:

&i2c1 {
default_device: default_device@75 {
    compatible = "some-name-never-mind";
     reg = <0x75>;
};
my_device: my_device@0 {
compatible = "my-device-which-do-only-some-minor-part";
reg = <0x75>;
};
};

You know what I mean, is it possible to declare in dts two kernel modules
for the same device with the same address? I don't want to extend
default_device functionality, I want put my functionality in separate
kernel module. I am currently in the middle of implementation but I wonder
if it has sense. Both kernel modules will have in fact:
probe(struct i2c_client *client, ...), I wonder if probe won't fail. At
least in user space shell "i2cdetect -r 1" returns UU for address 0x75 when
kernel module is loaded. So that is why I suspect probe might fail.

Another story is what in case somebody asks for access to device at the
same time from two kernel modules. I hope function:
i2c_smbus_write_byte_data
has some kind of spinlock, mutexes and just wait till bus is free, but who
knows.:)

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Re: two kernel modules for the same device address in dts

[Ezra Buehler]

Hi Tomek,

On 7 Apr 2020, at 15:26, Tomek The Messenger <tomekthemessenger@gmail.com> wrote:
> &i2c1 {
> default_device: default_device@75 {
>     compatible = "some-name-never-mind";
>      reg = <0x75>;
> };
> my_device: my_device@0 {
> compatible = "my-device-which-do-only-some-minor-part";
> reg = <0x75>;
> };
> };

I am not an expert here, I do not know what the best practice is.
But, I would do following:

/ {
(...)

    my_device: my_device@0 {
        default-device = <&default_device>;
    }

(...)
};

&i2c1 {
    default_device: default_device@75 {
        compatible = "some-name-never-mind";
        reg = <0x75>;
    };
};

Cheers,
Ezra.
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