Re: [PATCH 2/2] of: Warn when of_property_read_bool() is used on non-boolean properties

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Rob,

On Thu, Jan 9, 2025 at 8:42 PM Rob Herring (Arm) <robh@kernel.org> wrote:
> The use of of_property_read_bool() for non-boolean properties is
> deprecated. The primary use of it was to test property presence, but
> that has been replaced in favor of of_property_present(). With those
> uses now fixed, add a warning to discourage new ones.
>
> Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

Thanks for your patch, which is now commit c141ecc3cecd7647 ("of:
Warn when of_property_read_bool() is used on non-boolean properties")
in dt-rh/for-next.

I have bisected a failure in secondary CPU bring-up on R-Car H1 (quad
Cortex-A9 MPCore) to this commit:

     Detected Renesas R-Car Gen1 r8a7779 ES1.0
     smp: Bringing up secondary CPUs ...
    -CPU1: thread -1, cpu 1, socket 0, mpidr 80000001
    -CPU1: Spectre v2: using BPIALL workaround
    -CPU2: thread -1, cpu 2, socket 0, mpidr 80000002
    -CPU2: Spectre v2: using BPIALL workaround
    -CPU3: thread -1, cpu 3, socket 0, mpidr 80000003
    -CPU3: Spectre v2: using BPIALL workaround
    -smp: Brought up 1 node, 4 CPUs
    -SMP: Total of 4 processors activated (2000.00 BogoMIPS).
    +CPU1: failed to come online
    +CPU2: failed to come online
    +CPU3: failed to come online
    +smp: Brought up 1 node, 1 CPU
    +SMP: Total of 1 processors activated (500.00 BogoMIPS).
     CPU: All CPU(s) started in SVC mode.

Reverting this commit on top of my work tree fixes the issue, too.
However, I do not see how this commit could impact CPU bring-up?

I added debug code to of_property_read_bool(), to print all look-ups.
I only saw a few before CPU bring-up, nothing relevant:

     NR_IRQS: 16, nr_irqs: 16, preallocated irqs: 16
    +OF: of_property_read_bool(interrupt-controller): 1
     rcu: srcu_init: Setting srcu_struct sizes based on contention.
    +OF: of_property_read_bool(interrupt-controller): 1
     sched_clock: 64 bits at 250MHz, resolution 4ns, wraps every 4398046511102ns
     clocksource: arm_global_timer: mask: 0xffffffffffffffff
max_cycles: 0x7350b89c29, max_idle_ns: 881590431910 ns
     Switching to timer-based delay loop, resolution 4ns
    +OF: of_property_read_bool(interrupt-controller): 1
    +OF: of_property_read_bool(always-on): 0
     Console: colour dummy device 80x30
     printk: legacy console [tty0] enabled

Perhaps something shifted in the code layout?  The obvious suspects
(shmobile_boot_* and shmobile_smp_* asm code, secondary_startup(),
addresses in arch/arm/mach-shmobile/platsmp-scu.c) are still at the
same addresses as before...

Anyone with a clue?
Thanks!

> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -31,6 +31,32 @@
>
>  #include "of_private.h"
>
> +/**
> + * of_property_read_bool - Find a property
> + * @np:                device node from which the property value is to be read.
> + * @propname:  name of the property to be searched.
> + *
> + * Search for a boolean property in a device node. Usage on non-boolean
> + * property types is deprecated.
> + *
> + * Return: true if the property exists false otherwise.
> + */
> +bool of_property_read_bool(const struct device_node *np, const char *propname)
> +{
> +       struct property *prop = of_find_property(np, propname, NULL);
> +
> +       /*
> +        * Boolean properties should not have a value. Testing for property
> +        * presence should either use of_property_present() or just read the
> +        * property value and check the returned error code.
> +        */
> +       if (prop && prop->length)
> +               pr_warn("%pOF: Read of boolean property '%s' with a value.\n", np, propname);
> +
> +       return prop ? true : false;
> +}
> +EXPORT_SYMBOL(of_property_read_bool);
> +
>  /**
>   * of_graph_is_present() - check graph's presence
>   * @node: pointer to device_node containing graph port
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 1cb4eb7fc2eded2246c697c3bcaf1b85d43108ab..0cdd58ff0a4190724309ba1eddbac51b188b6136 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -311,6 +311,7 @@ extern struct device_node *of_find_node_with_property(
>  extern struct property *of_find_property(const struct device_node *np,
>                                          const char *name,
>                                          int *lenp);
> +extern bool of_property_read_bool(const struct device_node *np, const char *propname);
>  extern int of_property_count_elems_of_size(const struct device_node *np,
>                                 const char *propname, int elem_size);
>  extern int of_property_read_u32_index(const struct device_node *np,
> @@ -615,6 +616,12 @@ static inline struct device_node *of_find_compatible_node(
>         return NULL;
>  }
>
> +static inline bool of_property_read_bool(const struct device_node *np,
> +                                       const char *propname)
> +{
> +       return false;
> +}
> +
>  static inline int of_property_count_elems_of_size(const struct device_node *np,
>                         const char *propname, int elem_size)
>  {
> @@ -1242,24 +1249,6 @@ static inline int of_property_read_string_index(const struct device_node *np,
>         return rc < 0 ? rc : 0;
>  }
>
> -/**
> - * of_property_read_bool - Find a property
> - * @np:                device node from which the property value is to be read.
> - * @propname:  name of the property to be searched.
> - *
> - * Search for a boolean property in a device node. Usage on non-boolean
> - * property types is deprecated.
> - *
> - * Return: true if the property exists false otherwise.
> - */
> -static inline bool of_property_read_bool(const struct device_node *np,
> -                                        const char *propname)
> -{
> -       const struct property *prop = of_find_property(np, propname, NULL);
> -
> -       return prop ? true : false;
> -}
> -
>  /**
>   * of_property_present - Test if a property is present in a node
>   * @np:                device node to search for the property.

Gr{oetje,eeting}s,

                        Geert


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