Re: [PATCH net] net: stmmac: platform: guarantee uniqueness of bus_id

[Quentin Schulz]

Hi Abhishek,

On 5/30/25 12:16 AM, Abhishek Chauhan (ABC) wrote:
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>
> On 5/26/2025 1:26 PM, Paolo Abeni wrote:
> > On 5/21/25 5:21 PM, Quentin Schulz wrote:
> > > From: Quentin Schulz <quentin.schulz@xxxxxxxxx>
> > >
> > > bus_id is currently derived from the ethernetX alias. If one is missing
> > > for the device, 0 is used. If ethernet0 points to another stmmac device
> > > or if there are 2+ stmmac devices without an ethernet alias, then bus_id
> > > will be 0 for all of those.
> > >
> > > This is an issue because the bus_id is used to generate the mdio bus id
> > > (new_bus->id in drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
> > > stmmac_mdio_register) and this needs to be unique.
> > >
> > > This allows to avoid needing to define ethernet aliases for devices with
> > > multiple stmmac controllers (such as the Rockchip RK3588) for multiple
> > > stmmac devices to probe properly.
> > >
> > > Obviously, the bus_id isn't guaranteed to be stable across reboots if no
> > > alias is set for the device but that is easily fixed by simply adding an
> > > alias if this is desired.
> > >
> > > Signed-off-by: Quentin Schulz <quentin.schulz@xxxxxxxxx>
> >
> > I think no need to CC stable here, but you need to provide a suitable
> > fixes tag, thanks!
> Quentin to make your life easy.
> It fixes this patch
> https://lore.kernel.org/lkml/1372930541-19409-1-git-send-email-srinivas.kandagatla@xxxxxx/
> dt:net:stmmac: Add support to dwmac version 3.610 and 3.710
> It goes back in time to 2013 when this bus_id was introduced through dts

Fortunately, we ended up finding the same "culprit" (see v2 of my patch 
that got merged[1] :) )

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=eb7fd7aa35bfcc1e1fda4ecc42ccfcb526cdc780

Thanks!
Quentin