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

[Aswath Govindraju]

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;
        };

So, to distinguish nodes with same name, phandles can be used while
assigning sequence numbers.

Thanks,
Aswath

> 
>> +
>>                 val = trailing_strtol(name);
>>                 if (val != -1) {
>>                         *seqp = val;
>> --
>> 2.17.1
>>
> 
> Regards,
> Simon
>