Hi Simon, On Mon, Feb 8, 2021 at 12:21 PM Simon Glass <s...@chromium.org> wrote: > > Hi Bin, > > On Sun, 7 Feb 2021 at 08:11, Bin Meng <bmeng...@gmail.com> wrote: > > > > At present fdt_read_prop() can only handle 1 or 2 cells. It is > > called by fdt_read_range() which may be used to read PCI address > > from <ranges> for a PCI bus node where the number of PCI address > > cell is 3. > > > > This adds the special handling of such case. > > > > Signed-off-by: Bin Meng <bmeng...@gmail.com> > > --- > > > > common/fdt_support.c | 15 ++++++++++++--- > > 1 file changed, 12 insertions(+), 3 deletions(-) > > I think this is missing why it is needed. Also needs an update to > function to the comment in the header file. >
I will try to add more details in v2. The reason why this is needed is because in fdt_read_range() may be used to read PCI address from <ranges>. The <ranges> property is an array of { <child address> <parent address> <size in child address space> }. When trying to read <child address> from a PCI bus node using fdt_read_prop(), as the codes below: /* Read <child address> */ if (child_addr) { r = fdt_read_prop(ranges, ranges_len, cell, child_addr, acells); if (r) return r; } it will fail, because the PCI child address is made up of 3 cells but fdt_read_prop() cannot handle it. We advance the cell offset by 1 so that the <child address> can be correctly read. Regards, Bin