Re: [PATCH] of: Add of_get_memory_prop()

[rananta]

On 2019-09-18 13:13, Rob Herring wrote:
> On Wed, Sep 18, 2019 at 1:47 PM Raghavendra Rao Ananta
> <rananta@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> > ---
> >  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.
Sorry, can you please elaborate more on this? What do you mean by 
unit-address and working 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
- Raghavendra