On Fri, Aug 22, 2014 at 09:03:49PM -0600, Simon Glass wrote: > Hi Thierry, > > On 19 August 2014 07:06, Thierry Reding <thierry.reding@xxxxxxxxx> wrote: > > On Tue, Aug 19, 2014 at 06:52:22AM -0600, Simon Glass wrote: > >> Hi Theirry, > >> > >> > >> On 19 August 2014 04:59, Thierry Reding <thierry.reding@xxxxxxxxx> 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@xxxxxxxxx> > >> > wrote: > >> > > > From: Thierry Reding <treding@xxxxxxxxxx> > >> > > > > >> > > > 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@xxxxxxxxxx> > >> > > > --- > >> > > > 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? > > > > It doesn't explicitly warn about the properties being absent. Rather it > > will fallback to the default (#address-cells = <2>, #size-cells = <1> in > > the version that I have) and warn if those don't match what's expected. > > > > Interestingly as opposed to what the Linux kernel does, DTC doesn't seem > > to climb further up the tree if it can't find the properties in a device > > tree node. Instead, it seems to always use the default values instead. > > > > Adding the devicetree@xxxxxxxxxxxxxxx mailing list. Maybe somebody there > > can help iron out this inconsistency. ePAPR explicitly says that both > > "... #address-cells and #size-cells properties are not inherited from > > ancestors in the device tree. They shall be explicitly defined." (see > > 2.3.5 "#address-cells and #size-cells"). > > That's my understanding too. So should we drop this patch? Yes, in this particular case it works fine using the existing fdt_address_cells() and fdt_size_cells() functions so I've dropped this patch. Thierry
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