linux-kernel - Re: [PATCH] of: Add of_get_memory

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Date:   Wed, 18 Sep 2019 15:13:04 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Raghavendra Rao Ananta <rananta@...eaurora.org>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Trilok Soni <tsoni@...eaurora.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] of: Add of_get_memory_prop()

On Wed, Sep 18, 2019 at 1:47 PM Raghavendra Rao Ananta
<rananta@...eaurora.org> wrote:
>
> On some embedded systems, the '/memory' dt-property gets updated
> by the bootloader (for example, the DDR configuration) and then
> gets passed onto the kernel. The device drivers may have to read
> the properties at runtime to make decisions. Hence, add
> of_get_memory_prop() for the device drivers to query the requested

Function name doesn't match. Device drivers don't need to access the FDT.

> properties.
>
> Signed-off-by: Raghavendra Rao Ananta <rananta@...eaurora.org>
> ---
>  drivers/of/fdt.c       | 27 +++++++++++++++++++++++++++
>  include/linux/of_fdt.h |  1 +
>  2 files changed, 28 insertions(+)

We don't add kernel api's without users.

>
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 223d617ecfe1..925cf2852433 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -79,6 +79,33 @@ void __init of_fdt_limit_memory(int limit)
>         }
>  }
>
> +/**
> + * of_fdt_get_memory_prop - Return the requested property from the /memory node
> + *
> + * On match, returns a non-zero positive value which represents the property
> + * value. Otherwise returns -ENOENT.
> + */
> +int of_fdt_get_memory_prop(const char *pname)
> +{
> +       int memory;
> +       int len;
> +       fdt32_t *prop = NULL;
> +
> +       if (!pname)
> +               return -EINVAL;
> +
> +       memory = fdt_path_offset(initial_boot_params, "/memory");

Memory nodes should have a unit-address, so this won't work frequently.

> +       if (memory > 0)
> +               prop = fdt_getprop_w(initial_boot_params, memory,
> +                                 pname, &len);
> +
> +       if (!prop || len != sizeof(u32))
> +               return -ENOENT;
> +
> +       return fdt32_to_cpu(*prop);
> +}
> +EXPORT_SYMBOL_GPL(of_fdt_get_memory_prop);
> +
>  static bool of_fdt_device_is_available(const void *blob, unsigned long node)
>  {
>         const char *status = fdt_getprop(blob, node, "status", NULL);
> diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h
> index acf820e88952..537f29373358 100644
> --- a/include/linux/of_fdt.h
> +++ b/include/linux/of_fdt.h
> @@ -38,6 +38,7 @@ extern char __dtb_end[];
>  /* Other Prototypes */
>  extern u64 of_flat_dt_translate_address(unsigned long node);
>  extern void of_fdt_limit_memory(int limit);
> +extern int of_fdt_get_memory_prop(const char *pname);
>  #endif /* CONFIG_OF_FLATTREE */
>
>  #ifdef CONFIG_OF_EARLY_FLATTREE
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>