linux-kernel - Re: [PATCH v2 1/2] of: platform: Make sure bus only devices get probed

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Message-ID: <CAPDyKFpP6pSRSw8_OAW8+ZJNH+CwXtfWBNDcD182gQmzqW=O5g@mail.gmail.com>
Date:   Fri, 3 Sep 2021 11:18:48 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Android Kernel Team <kernel-team@...roid.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] of: platform: Make sure bus only devices get probed

On Fri, 3 Sept 2021 at 01:04, Saravana Kannan <saravanak@...gle.com> wrote:
>
> fw_devlink could end up creating device links for bus only devices.
> However, bus only devices don't get probed and can block probe() or
> sync_state() [1] call backs of other devices. To avoid this, set up
> these devices to get probed by the simple-pm-bus.
>
> [1] - https://lore.kernel.org/lkml/CAPDyKFo9Bxremkb1dDrr4OcXSpE0keVze94Cm=zrkOVxHHxBmQ@mail.gmail.com/
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> Tested-by: Saravana Kannan <saravanak@...gle.com>

Again, this looks like a nice solution to the problem.

One question though. The Kconfig SIMPLE_PM_BUS, should probably be
"default y" - or something along those lines to make sure fw_devlink
works as expected.

Kind regards
Uffe


> ---
>  drivers/of/platform.c | 45 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
>
> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> index 74afbb7a4f5e..b010e2310131 100644
> --- a/drivers/of/platform.c
> +++ b/drivers/of/platform.c
> @@ -97,6 +97,48 @@ static void of_device_make_bus_id(struct device *dev)
>         }
>  }
>
> +/**
> + * of_match_only_simple_bus - Check if a device node is only a simple bus
> + * @np: device node to check
> + *
> + * A simple bus in this context is defined as a transparent bus whose child
> + * devices are automatically populated but has no hardware specific
> + * functionality.
> + *
> + * Returns true if the device node is only a simple bus and can never match
> + * with any other specific driver.  Otherwise, returns false.
> + */
> +static bool of_match_only_simple_bus(struct device_node *np)
> +{
> +       /* List of buses that don't have an explicit driver. */
> +       static const char * const of_simple_bus_table[] = {
> +               "simple-bus",
> +               "simple-mfd",
> +               "isa",
> +               "arm,amba-bus",
> +       };
> +       const char *cp;
> +       struct property *prop;
> +       int i;
> +
> +       prop = of_find_property(np, "compatible", NULL);
> +       for (cp = of_prop_next_string(prop, NULL); cp;
> +            cp = of_prop_next_string(prop, cp)) {
> +               bool match = false;
> +               const char *bus = of_simple_bus_table[i];
> +
> +               for (i = 0; i < ARRAY_SIZE(of_simple_bus_table); i++)
> +                       if (!of_compat_cmp(cp, bus, strlen(bus))) {
> +                               match = true;
> +                               break;
> +                       }
> +               if (!match)
> +                       return false;
> +       }
> +
> +       return true;
> +}
> +
>  /**
>   * of_device_alloc - Allocate and initialize an of_device
>   * @np: device node to assign to device
> @@ -143,6 +185,9 @@ struct platform_device *of_device_alloc(struct device_node *np,
>         dev->dev.fwnode = &np->fwnode;
>         dev->dev.parent = parent ? : &platform_bus;
>
> +       if (of_match_only_simple_bus(np))
> +               dev->driver_override = "simple-pm-bus";
> +
>         if (bus_id)
>                 dev_set_name(&dev->dev, "%s", bus_id);
>         else
> --
> 2.33.0.153.gba50c8fa24-goog
>