[RESEND PATCH] fdt: Use phandle to distinguish DT nodes with same name

[Simon Glass]

Hi,

On Wed, 18 Nov 2020 at 10:55, Vignesh Raghavendra <vigneshr at ti.com> wrote:
>
>
>
> On 11/18/20 8:44 PM, Aswath Govindraju wrote:
> > Hi Simon,
> >
> > On 18/11/20 8:07 pm, Simon Glass wrote:
> >> Hi Aswath,
> >>
> >> On Mon, 16 Nov 2020 at 07:29, Aswath Govindraju <a-govindraju at ti.com> wrote:
> >>>
> >>> While assigning the sequence number to subsystem instances by reading the
> >>> aliases property, only DT nodes names are compared and not the complete
> >>> path. This causes a problem when there are two DT nodes with same name but
> >>> have different paths.
> >>>
> >>> Fix it by comparing the phandles of DT nodes after the node names match.
> >>>
> >>> Signed-off-by: Aswath Govindraju <a-govindraju at ti.com>
> >>> ---
> >>>
> >>> Resending this patch as it was held awaiting for moderator approval because
> >>> patch was sent by non-member.
> >>>
> >>>  lib/fdtdec.c | 5 +++++
> >>>  1 file changed, 5 insertions(+)
> >>>
> >>> diff --git a/lib/fdtdec.c b/lib/fdtdec.c
> >>> index 2015907dee7d..9e1bfe0b519e 100644
> >>> --- a/lib/fdtdec.c
> >>> +++ b/lib/fdtdec.c
> >>> @@ -478,6 +478,11 @@ int fdtdec_get_alias_seq(const void *blob, const char *base, int offset,
> >>>                 slash = strrchr(prop, '/');
> >>>                 if (strcmp(slash + 1, find_name))
> >>>                         continue;
> >>> +
> >>> +               if (fdt_get_phandle(blob, offset) !=
> >>> +                   fdt_get_phandle(blob, fdt_path_offset(blob, prop)))
> >>> +                       continue;
> >>
> >> The call to fdt_path_offset() is very slow. Perhaps we can do this
> >> check only with livetree? What situation is causing a problem for you?
> >> What are the node / alias names?
> >
> > In the case of live tree for getting the sequence number the node
> > pointers are compared. So, I don't think this problem would come up.
> >
> > As for the use case,
> >
> > In AM654 Device tree there are two instances of USB controllers and both
> > the controller nodes have the same name usb at 10000
> >
> > If dfu is performed through the port connected to second controller.
> > Then based on the dr_mode of first controller the instance number to be
> > used in dfu command will vary. In order to make the instance number for
> > dfu command to be independent, aliases can be used(If aliases are
> > defined then the sequence number is assigned as the alias number.).
> >
> > The problem with current method for acquiring sequence number using
> > aliases is that only the name of the node is compared with node name
> > from the aliases property. So in the above case both the controllers
> > will have the same name. This leads to the first alias number being used
> > for the both the controllers to assign sequence number.
> >
> >
> > aliases {
> >                 serial2 = &main_uart0;
> >                 ethernet0 = &cpsw_port1;
> >                 usb0 = &usb0;            // This property being used to
> >                                       //alias both the controllers
> >                 usb1 = &usb1;
> >         };
>
>
> To explain a bit more, here is the DT snippet around usb0 and usb1
>
>         dwc3_0: dwc3 at 4000000 {
>                 compatible = "ti,am654-dwc3";
>                 reg = <0x0 0x4000000 0x0 0x4000>;
>                 #address-cells = <1>;
>                 #size-cells = <1>;
>                 ranges = <0x0 0x0 0x4000000 0x20000>;
>                 ...
>
>                 usb0: usb at 10000 {
>                         compatible = "snps,dwc3";
>                         reg = <0x10000 0x10000>;
>                         ...
>                 };
>         };
>
>         dwc3_1: dwc3 at 4020000 {
>                 compatible = "ti,am654-dwc3";
>                 reg = <0x0 0x4020000 0x0 0x4000>;
>                 #address-cells = <1>;
>                 #size-cells = <1>;
>                 ranges = <0x0 0x0 0x4020000 0x20000>;
>                 ...
>
>                 usb1: usb at 10000 {
>                         compatible = "snps,dwc3";
>                         reg = <0x10000 0x10000>;
>                         ...
>                 };
>         };
>
> In above case, (with CONFIG_OF_LIVE disabled),
> fdtdec_get_alias_seq() fails to pick the correct instance for USB
> controller for a given index. This is because fdtdec_get_alias_seq()
> only compares the leaf node name (usb at 10000) with alias path and thus
> both usb instances match to usb0.
>
> >
> > So, to distinguish nodes with same name, phandles can be used while
> > assigning sequence numbers.

Thank you both for the detai. I understand it and in fact I think this
has come up before.

Would it be OK to use livetree?

If not, can we put this code behind a Kconfig so the extra time
penalty is only incurred on boards that need it?

Regards,
Simon