[U-Boot] [PATCH 01/23] fdt: Add functions to query a node's #address- and #size-cells

Simon Glass
2014-08-19T12:52:22Z

Hi Theirry,

On 19 August 2014 04:59, Thierry Reding <thierry.reding@gmail.com> wrote:

> On Mon, Aug 18, 2014 at 11:52:36AM -0600, Simon Glass wrote:
> > Hi Thierry,
> >
> > On 18 August 2014 01:16, Thierry Reding <thierry.reding@gmail.com>
> wrote:
> > > From: Thierry Reding <treding@nvidia.com>
> > >
> > > Given a device tree node, the fdt_n_addr_cells() function will walk up
> > > the device tree and search for an #address-cells property. It returns
> > > the number of cells required by the device tree node to represent an
> > > address.
> > >
> > > Similarly the fdt_n_size_cells() function returns the number of cells
> > > required by the given device tree node to represent a size. It achieves
> > > that by walking up the device tree in seach for a #size-cells property.
> > >
> > > If no #address-cells or #size-cells property can be found, both of the
> > > functions return 1.
> > >
> > > Signed-off-by: Thierry Reding <treding@nvidia.com>
> > > ---
> > > include/libfdt.h | 28 ++++++++++++++++++++++++++++
> > > lib/libfdt/fdt_ro.c | 36 ++++++++++++++++++++++++++++++++++++
> > > 2 files changed, 64 insertions(+)
> > >
> > > diff --git a/include/libfdt.h b/include/libfdt.h
> > > index a1ef1e15df3d..e7f991b388cf 100644
> > > --- a/include/libfdt.h
> > > +++ b/include/libfdt.h
> > > @@ -1638,4 +1638,32 @@ int fdt_find_regions(const void *fdt, char *
> const inc[], int inc_count,
> > > struct fdt_region region[], int max_regions,
> > > char *path, int path_len, int add_string_tab);
> > >
> > > +/**
> > > + * fdt_n_addr_cells() - find the number of address cells required by
> a node
> > > + *
> > > + * Looks up the #address-cells property of the node to examine. If
> that has
> > > + * no such property, walks up the device tree until it finds one in
> one of
> > > + * the device's parents. If no #address-cells property is found, it is
> > > + * assumed to be 1.
> > > + *
> > > + * @param fdt FDT blob
> > > + * @param node node to examine
> > > + * @return number of address cells
> > > + */
> > > +int fdt_n_addr_cells(const void *fdt, int node);
> >
> > There is a new fdt_address_cells() recently that looks suitable.
> >
> > > +
> > > +/**
> > > + * fdt_n_size_cells() - find the number of size cells required by a
> node
> >
> > Also fdt_size_cells().
>
> Neither of those seem to walk up the tree, so inheriting #address-cells
> or #size-cells from a parent will not work.
>
> According to the comments in the code they're also supposed to return
> the number of cells represented by a bus, not a device (which might
> explain why it doesn't walk up the tree).
>
> I also can't reuse them to implement these fdt_n_addr_cells() and
> fdt_n_size_cells() functions because they don't return an accurate error
> if the #address-cells and #size-cells are not found, therefore it's
> impossible to decide when to climb further up the tree.
>

OK but I have one more question. I thought that dtc gave a warning when you
don't explicitly specify these values in the parent node?

Regards,
Simon