Date: Wed, 10 Jan 2024 10:26:54 +0300
From: Arınç ÜNAL <arinc.unal@...nc9.com>
To: Vladimir Oltean <olteanv@...il.com>
Cc: Dan Carpenter <dan.carpenter@...aro.org>, Simon Horman
 <horms@...nel.org>, Daniel Golle <daniel@...rotopia.org>,
 Landen Chao <Landen.Chao@...iatek.com>, DENG Qingfang <dqfext@...il.com>,
 Sean Wang <sean.wang@...iatek.com>, Andrew Lunn <andrew@...n.ch>,
 Florian Fainelli <f.fainelli@...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>,
 Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org,
 Frank Wunderlich <frank-w@...lic-files.de>,
 Bartel Eerdekens <bartel.eerdekens@...stell8.be>, mithat.guner@...ont.com,
 erkin.bozoglu@...ont.com
Subject: Re: [PATCH net-next 07/15] net: dsa: mt7530: do not run
 mt7530_setup_port5() if port 5 is disabled

On 9.01.2024 17:57, Vladimir Oltean wrote:
> Yes, well _now_ it is a false positive, probably because smatch cannot
> determine that when priv->p5_intf_sel has been set to P5_INTF_SEL_PHY_P0
> or P5_INTF_SEL_PHY_P4, "interface" should have been also initialized.
> But it doesn't matter, you can ignore a false positive. I'm also seeing it.
> Although you should check whether treating -ENODEV as a hard error is fine
> and won't cause regressions.
> 
>> Just so you know, I intend to remove this whole PHY muxing feature once I
>> bring changing DSA conduit support to this subdriver. I've got two strong
>> reasons for this.
>> - Changing the DSA conduit achieves the same result with the only overhead
>>    being the DSA header included on every frame.
>>
>> - There can't be proper dt-bindings for it as the nature of the feature
>>    shows that it represents an optional way to operate the hardware, it does
>>    not represent a hardware design. Overall, the implementation is a hack to
>>    make it work for specific hardware (switch must be connected to gmac1 of
>>    a MediaTek SoC, no PHY must be present at address 0 or 4 on the MDIO bus
>>    of the SoC. It should rather be configurable on userspace. Which will
>>    never happen as it is specific to this switch and the changing DSA
>>    conduit feature is the perfect substitute for this.
> 
> Is PHY muxing a "true" switch bypass, or is it just a route through the
> switch for all packets coming from GMAC5 to go to phy0 or phy4? If the
> latter, I agree that dynamic conduit changing is a more flexible option,
> not to mention the user space tooling is already there.

It's the latter, and that's exactly what I think.

> 
> Are there existing systems that use PHY muxing? The possible problem I
> see is breaking those boards which have a phy-handle on gmac5, if the
> mt7530 driver is no longer going to modify its HWTRAP register.

Ah see, for PHY muxing, the driver actually wants the phy-handle to be put
on the SoC MAC, and the PHY to be defined on the SoC ethernet's MDIO bus.
We don't even define gmac5 as a port on the switch dt-bindings.

While none of the DTs on the Linux repository utilise this, some of the
mt7621 DTs on OpenWrt do. The change in behaviour will only be that phy0/4
will be inaccessible from the SoC MAC's network interface. I de-facto
maintain the mt7621 device tree source files there. I intend to revert it
along with adding port 5 as a CPU port so that the conduit changing feature
becomes available.

> 
>>
>> Let me know if you've got any suggestions that can get rid of the warning
>> without reworking the whole code block. Otherwise, I'm just going to ignore
>> it until I get rid of the whole code block.
> 
> The obvious way would be to leave the initialization to PHY_INTERFACE_MODE_NA
> there. Or to just ignore the warning.

I'll ignore.

Arınç

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