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

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Message-ID: <20230203231815.mue2aeynxuwqpuzr@skbuf>
Date:   Sat, 4 Feb 2023 01:18:15 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Rakesh Sankaranarayanan <rakesh.sankaranarayanan@...rochip.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        andrew@...n.ch, f.fainelli@...il.com, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        woojung.huh@...rochip.com, UNGLinuxDriver@...rochip.com,
        linux@...linux.org.uk
Subject: Re: [RFC PATCH net-next 02/11] net: dsa: microchip: lan937x: update
 SMI index

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@...rochip.com>
> ---

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.