Re: [RFC PATCH net-next 02/11] net: dsa: microchip: lan937x: update SMI index

[Vladimir Oltean]

On Thu, Feb 02, 2023 at 06:29:21PM +0530, Rakesh Sankaranarayanan wrote:
> Current DSA driver register mdio interface for a port in the
> format of SMI-switch_index:port_number, switch_index is derived
> using variable ds->index. For a single switch ds->index will be
> always zero, and for cascaded switch, ds->index should be one.
> But it is found that ds->index is getting updated only after
> mdio_register stage. Update mdio_register to use variable directly
> from device tree using "dsa,member" identifier.
> 
> Signed-off-by: Rakesh Sankaranarayanan <rakesh.sankaranarayanan@xxxxxxxxxxxxx>
> ---

Impossible, check again.

The call path is:

ksz_switch_register()
-> dsa_register_switch()
   -> dsa_switch_probe()
      -> dsa_switch_parse_of()
         -> dsa_switch_parse_member_of()
            -> sets ds->index
      -> dsa_tree_setup()
         -> dsa_tree_setup_switches()
            -> dsa_switch_setup()
               -> ksz_setup()
                  -> ksz_mdio_register()
                     -> you claim ds->index isn't set

You don't even need to be an expert on the code path, you can grep for
"ds->index = ", put a dump_stack() where it's set and one where you need
it, and compare in the stack trace which functions are common and where
they diverge.