Re: I2C device tree driver compatible strings

[Geert Uytterhoeven <geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org>]

CC linux-i2c

On Sat, Apr 11, 2015 at 9:36 PM, Jakub Kiciński <moorray3-5tc4TXWwyLM@public.gmane.org> wrote:
> Hello,
>
> sc16is7xx declares two device id tables, one with OF ids:
>
> static const struct of_device_id __maybe_unused sc16is7xx_dt_ids[] = {
>         { .compatible = "nxp,sc16is740",        .data = &sc16is74x_devtype, },
>         { .compatible = "nxp,sc16is741",        .data = &sc16is74x_devtype, },
>         { .compatible = "nxp,sc16is750",        .data = &sc16is750_devtype, },
>         { .compatible = "nxp,sc16is752",        .data = &sc16is752_devtype, },
>         { .compatible = "nxp,sc16is760",        .data = &sc16is760_devtype, },
>         { .compatible = "nxp,sc16is762",        .data = &sc16is762_devtype, },
>         { }
> };
> MODULE_DEVICE_TABLE(of, sc16is7xx_dt_ids);
>
> and one with i2c ids:
>
> static const struct i2c_device_id sc16is7xx_i2c_id_table[] = {
>         { "sc16is74x",  (kernel_ulong_t)&sc16is74x_devtype, },
>         { "sc16is750",  (kernel_ulong_t)&sc16is750_devtype, },
>         { "sc16is752",  (kernel_ulong_t)&sc16is752_devtype, },
>         { "sc16is760",  (kernel_ulong_t)&sc16is760_devtype, },
>         { "sc16is762",  (kernel_ulong_t)&sc16is762_devtype, },
>         { }
> };
> MODULE_DEVICE_TABLE(i2c, sc16is7xx_i2c_id_table);
>
> I declare my device in DT under I2C controller as
>>       compatible = "nxp,sc16is740";
> However, the driver does not get loaded automatically because its
> i2c id table contains "sc16is74x" instead of "sc16is740".
>
> I have three questions:
>
> (1) What is the relation between i2c_device_id and of_device_id strings
>     and why does the driver define both?
>
> (2) What are the rules for loading i2c drivers based on DT and why is the
>     driver not loaded even though its compatible with one of the OF ids?
>
> (3) Is it OK for the driver to define incompatible strings or should I
>     correct them like this (keeping the old entry for backwards
>     compatibility):
>
> diff --git a/drivers/tty/serial/sc16is7xx.c
> b/drivers/tty/serial/sc16is7xx.c index eaf0008a39cb..efe286d00174 100644
> --- a/drivers/tty/serial/sc16is7xx.c
> +++ b/drivers/tty/serial/sc16is7xx.c
> @@ -1219,6 +1219,8 @@ static int sc16is7xx_i2c_remove(struct i2c_client
> *client)
>  static const struct i2c_device_id sc16is7xx_i2c_id_table[] = {
>         { "sc16is74x",  (kernel_ulong_t)&sc16is74x_devtype, },
> +       { "sc16is740",  (kernel_ulong_t)&sc16is74x_devtype, },
> +       { "sc16is741",  (kernel_ulong_t)&sc16is74x_devtype, },
>         { "sc16is750",  (kernel_ulong_t)&sc16is750_devtype, },
>         { "sc16is752",  (kernel_ulong_t)&sc16is752_devtype, },
>         { "sc16is760",  (kernel_ulong_t)&sc16is760_devtype, },
>
>
> Thanks,
> Kuba
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