[PATCH 03/26] common: fdt_support: Support special case of PCI address in fdt_read_prop()

[Bin Meng <bmeng.cn@gmail.com>]

Hi Simon,

On Mon, Feb 8, 2021 at 12:21 PM Simon Glass <sjg@chromium.org> wrote:
>
> Hi Bin,
>
> On Sun, 7 Feb 2021 at 08:11, Bin Meng <bmeng.cn@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.cn@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