linux-kernel - Re: [PATCH] spi: mark device nodes only in case of successful instantiation

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Date:   Sun, 16 Oct 2016 10:49:11 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Ralf Ramsauer <ralf@...ses-pyramidenbau.de>
Cc:     Mark Brown <broonie@...nel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Wolfram Sang <wsa@...-dreams.de>,
        Linux I2C <linux-i2c@...r.kernel.org>
Subject: Re: [PATCH] spi: mark device nodes only in case of successful instantiation

Hi Ralf,

(Cc i2c)

On Fri, Oct 14, 2016 at 9:31 PM, Ralf Ramsauer
<ralf@...ses-pyramidenbau.de> wrote:
> Instantiated SPI device nodes are marked with OF_POPULATE. This was
> introduced in bd6c164. On unloading, loaded device nodes will of course
> be unmarked. The problem are nodes the fail during initialisation: If a
> node failed during registration, it won't be unloaded and hence never be
> unmarked again.
>
> So if a SPI driver module is unloaded and reloaded, it will skip nodes
> that failed before.
>
> Skip device nodes that are already populated and mark them only in case
> of success.
>
> Fixes: bd6c164 ("spi: Mark instantiated device nodes with OF_POPULATE")
> Signed-off-by: Ralf Ramsauer <ralf@...ses-pyramidenbau.de>
> Cc: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> Hi,
>
> imagine the following situation: you loaded a spi driver as module, but
> it fails to instantiate, because of some reasons (e.g. some resources,
> like gpios, might be in use in userspace).
>
> When reloading the driver, _all_ nodes, including previously failed
> ones, should be probed again. This is not the case at the moment.
> Current behaviour only re-registers nodes that were previously
> successfully loaded.
>
> This small patches fixes this behaviour. I stumbled over this while
> working on a spi driver.

Thanks for your patch!

>  drivers/spi/spi.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index 200ca22..f96a04e 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -1604,12 +1604,15 @@ static void of_register_spi_devices(struct spi_master *master)
>                 return;
>
>         for_each_available_child_of_node(master->dev.of_node, nc) {
> -               if (of_node_test_and_set_flag(nc, OF_POPULATED))
> +               if (of_node_check_flag(nc, OF_POPULATED))
>                         continue;
>                 spi = of_register_spi_device(master, nc);
> -               if (IS_ERR(spi))
> +               if (IS_ERR(spi)) {
>                         dev_warn(&master->dev, "Failed to create SPI device for %s\n",
>                                 nc->full_name);
> +                       continue;
> +               }
> +               of_node_set_flag(nc, OF_POPULATED);

I think it's safer to keep the atomic test-and-set, but clear the flag on
failure, cfr. of_platform_device_create_pdata() and of_amba_device_create().

Shouldn't of_spi_notify() be fixed, too?

The same issue exists for i2c in of_i2c_register_devices() and of_i2c_notify(),
which is what I had used as an example.

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