linux-kernel - Re: [RFC PATCH 3/7] i2c: allow DT nodes without 'compatible'

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Date:   Fri, 21 Feb 2020 10:45:57 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc:     Linux I2C <linux-i2c@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        linux-i3c@...ts.infradead.org,
        Kieran Bingham <kieran@...uared.org.uk>,
        Niklas Söderlund <niklas.soderlund@...natech.se>,
        Luca Ceresoli <luca@...aceresoli.net>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [RFC PATCH 3/7] i2c: allow DT nodes without 'compatible'

Hi Wolfram,

On Thu, Feb 20, 2020 at 6:26 PM Wolfram Sang
<wsa+renesas@...g-engineering.com> wrote:
> Sometimes, we have unknown devices in a system and still want to block
> their address. For that, we allow DT nodes with only a 'reg' property.
> These devices will be bound to the "dummy" driver but with the name
> "reserved". That way, we can distinguish them and even hand them over to
> the "dummy" driver later when they are really requested using
> i2c_new_ancillary_device().
>
> Signed-off-by: Wolfram Sang <wsa+renesas@...g-engineering.com>

Thanks for your patch!

Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
but one question below.

> --- a/Documentation/devicetree/bindings/i2c/i2c-ocores.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c-ocores.txt
> @@ -50,7 +50,6 @@ Examples:
>                 reg-io-width = <1>;     /* 8 bit read/write */
>
>                 dummy@60 {
> -                       compatible = "dummy";
>                         reg = <0x60>;
>                 };
>         };

There's a second instance to remove 18 lines below.

> --- a/drivers/i2c/i2c-core-of.c
> +++ b/drivers/i2c/i2c-core-of.c
> @@ -27,17 +27,15 @@ int of_i2c_get_board_info(struct device *dev, struct device_node *node,
>
>         memset(info, 0, sizeof(*info));
>
> -       if (of_modalias_node(node, info->type, sizeof(info->type)) < 0) {
> -               dev_err(dev, "of_i2c: modalias failure on %pOF\n", node);
> -               return -EINVAL;
> -       }
> -
>         ret = of_property_read_u32(node, "reg", &addr);
>         if (ret) {
>                 dev_err(dev, "of_i2c: invalid reg on %pOF\n", node);
>                 return ret;
>         }
>
> +       if (of_modalias_node(node, info->type, sizeof(info->type)) < 0)
> +               strlcpy(info->type, I2C_RESERVED_DRV_NAME, sizeof(I2C_RESERVED_DRV_NAME));

Could this cause a regression, e.g. if people already have such dummy
nodes in their DTS, and use sysfs new_device from userspace to
instantiate the device later?

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