linux-kernel - Re: [PATCH 06/12] i2c: rcar: set device parent and of

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Message-ID: <CAMuHMdW5ffiW_vEuDjV5bnmTeduhoqph7t8rsaFEVO7RXOM8jg@mail.gmail.com>
Date: Tue, 6 Jan 2026 10:13:51 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>
Cc: Wolfram Sang <wsa+renesas@...g-engineering.com>, 
	Mukesh Kumar Savaliya <mukesh.savaliya@....qualcomm.com>, 
	Viken Dadhaniya <viken.dadhaniya@....qualcomm.com>, Andi Shyti <andi.shyti@...nel.org>, 
	Florian Fainelli <florian.fainelli@...adcom.com>, Ray Jui <rjui@...adcom.com>, 
	Scott Branden <sbranden@...adcom.com>, 
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, Vignesh R <vigneshr@...com>, 
	Aaro Koskinen <aaro.koskinen@....fi>, Janusz Krzysztofik <jmkrzyszt@...il.com>, 
	Tony Lindgren <tony@...mide.com>, Andreas Kemnade <andreas@...nade.info>, 
	Kevin Hilman <khilman@...libre.com>, Roger Quadros <rogerq@...nel.org>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Magnus Damm <magnus.damm@...il.com>, 
	Patrice Chotard <patrice.chotard@...s.st.com>, Shawn Guo <shawnguo@...nel.org>, 
	Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>, 
	Fabio Estevam <festevam@...il.com>, Linus Walleij <linusw@...nel.org>, 
	Bartosz Golaszewski <brgl@...nel.org>, linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, linux-omap@...r.kernel.org, 
	linux-renesas-soc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	imx@...ts.linux.dev, linux-rpi-kernel@...ts.infradead.org
Subject: Re: [PATCH 06/12] i2c: rcar: set device parent and of_node through
 the adapter struct

Hi Bartosz,

On Tue, 23 Dec 2025 at 11:05, Bartosz Golaszewski
<bartosz.golaszewski@....qualcomm.com> 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@....qualcomm.com>

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@...ux-m68k.org

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