Re: [PATCH 06/12] i2c: rcar: set device parent and of_node through the adapter struct

[Geert Uytterhoeven]

Hi Bartosz,

On Tue, 23 Dec 2025 at 11:05, Bartosz Golaszewski
<bartosz.golaszewski@xxxxxxxxxxxxxxxx> wrote:
> Configure the parent device and the OF-node using dedicated fields in
> struct i2c_adapter and avoid dereferencing the internal struct device.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxxxxxxxx>

Thanks for your patch!

> --- a/drivers/i2c/busses/i2c-rcar.c
> +++ b/drivers/i2c/busses/i2c-rcar.c
> @@ -1149,8 +1149,8 @@ static int rcar_i2c_probe(struct platform_device *pdev)
>         adap->algo = &rcar_i2c_algo;
>         adap->class = I2C_CLASS_DEPRECATED;
>         adap->retries = 3;
> -       adap->dev.parent = dev;
> -       adap->dev.of_node = dev->of_node;
> +       adap->parent = dev;
> +       adap->of_node = dev->of_node;
>         adap->bus_recovery_info = &rcar_i2c_bri;
>         adap->quirks = &rcar_i2c_quirks;
>         i2c_set_adapdata(adap, priv);

    [....]
    ret = rcar_i2c_clock_calculate(priv);
    [...]
    ret = i2c_add_numbered_adapter(adap);

As rcar_i2c_clock_calculate() uses rcar_i2c_priv_to_dev(priv):

    #define rcar_i2c_priv_to_dev(p)         ((p)->adap.dev.parent)

I believe this will deference dev.parent before it is initialized by
the newly added code in i2c_register_adapter().

Let's check...

    Unable to handle kernel NULL pointer dereference at virtual
address 0000024c when read
    [0000024c] *pgd=80000040004003, *pmd=00000000
    Internal error: Oops: 206 [#1] SMP ARM
    Modules linked in:
    CPU: 1 UID: 0 PID: 1 Comm: swapper/0 Not tainted
6.19.0-rc3-koelsch-04401-g9e22366a23cd #2288 NONE
    Hardware name: Generic R-Car Gen2 (Flattened Device Tree)
    PC is at device_property_read_u32_array+0x0/0x14
    LR is at i2c_parse_timing+0x14/0x30
    [...]
    Call trace:
     device_property_read_u32_array from i2c_parse_timing+0x14/0x30
     i2c_parse_timing from i2c_parse_fw_timings+0x28/0x12c
     i2c_parse_fw_timings from rcar_i2c_probe+0x1cc/0x534
     rcar_i2c_probe from platform_probe+0x58/0x90

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds