On Mon, Aug 18, 2014 at 11:52:36AM -0600, Simon Glass wrote: > Hi Thierry, > > On 18 August 2014 01:16, Thierry Reding <[email protected]> wrote: > > From: Thierry Reding <[email protected]> > > > > 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 <[email protected]> > > --- > > 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. Thierry
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