linux-kernel - Re: [PATCH net] net: dsa: mt7530: fix impossible MDIO address and issue warning

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Message-ID: <20240430200844.GE2575892@kernel.org>
Date: Tue, 30 Apr 2024 21:08:44 +0100
From: Simon Horman <horms@...nel.org>
To: Daniel Golle <daniel@...rotopia.org>
Cc: Arınç ÜNAL <arinc.unal@...nc9.com>,
	Felix Fietkau <nbd@....name>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	DENG Qingfang <dqfext@...il.com>,
	Sean Wang <sean.wang@...iatek.com>, Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	Vladimir Oltean <olteanv@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Landen Chao <Landen.Chao@...iatek.com>, devicetree@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net] net: dsa: mt7530: fix impossible MDIO address and
 issue warning

On Tue, Apr 30, 2024 at 12:45:46AM +0100, Daniel Golle wrote:
> The MDIO address of the MT7530 and MT7531 switch ICs can be configured
> using bootstrap pins. However, there are only 4 possible options for the
> switch itself: 7, 15, 23 and 31 (ie. only 3 and 4 can be configured, bit
> 0~2 are always 111). Practically all boards known as of today use the
> default setting which is to have the switch respond to address 31, while
> the built-in switch PHYs respond to address 0~4 in this case.
> 
> However, even in MediaTek's SDK the address of the switch is wrongly
> stated in the device trees as 0 (while in reality it is 31), so warn the
> user about such broken device tree and make a good guess what was
> actually intended.
> 
> This is imporant to not break compatibility with older Device Trees as
> with commit 868ff5f4944a ("net: dsa: mt7530-mdio: read PHY address of
> switch from device tree") the address in device tree will be taken into
> account. Doing so instead of assuming the switch is always at
> address 31 which was previously hard-coded will obviously break things
> for many existing downstream device trees as they contain the wrong
> address (0) which previously didn't matter.
> 
> Fixes: b8f126a8d543 ("net-next: dsa: add dsa support for Mediatek MT7530 switch")
> Signed-off-by: Daniel Golle <daniel@...rotopia.org>

The cited commit is present in net-next but not net.
So I think this patch should target net-next.

..