linux-kernel - Re: [PATCH net] net: stmmac: platform: guarantee uniqueness of bus

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Message-ID: <36a5fe83-0bb3-4df0-9fb7-bfdc849ce715@quicinc.com>
Date: Mon, 2 Jun 2025 10:56:18 -0700
From: "Abhishek Chauhan (ABC)" <quic_abchauha@...cinc.com>
To: Quentin Schulz <quentin.schulz@...rry.de>,
        Paolo Abeni
	<pabeni@...hat.com>,
        Quentin Schulz <foss+kernel@...il.net>,
        Andrew Lunn
	<andrew+netdev@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Maxime
 Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue
	<alexandre.torgue@...s.st.com>
CC: Jakob Unterwurzacher <jakob.unterwurzacher@...rry.de>,
        Heiko Stuebner
	<heiko@...ech.de>, <netdev@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: stmmac: platform: guarantee uniqueness of bus_id



On 6/2/2025 2:38 AM, Quentin Schulz wrote:
> Hi Abhishek,
> 
> On 5/30/25 12:16 AM, Abhishek Chauhan (ABC) wrote:
>> [Some people who received this message don't often get email from quic_abchauha@...cinc.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>>
>> 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@...rry.de>
>>>>
>>>> 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@...rry.de>
>>>
>>> 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@st.com/
>> 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
> Nice!. Anyway i really like this fix because mdio creates a directory and if there are 2+ macs the directory creation will fail because 
two emac will have the same mdio directory names provided if someone forgets to mention alias in the dtsi. 
> Thanks!
> Quentin