linux-kernel - Re: [PATCH net-next v4 06/11] net: stmmac: resetup XPCS according to the new interface mode

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Date: Thu, 15 Feb 2024 11:14:27 +0800
From: Choong Yong Liang <yong.liang.choong@...ux.intel.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Rajneesh Bhardwaj <irenic.rajneesh@...il.com>,
 David E Box <david.e.box@...ux.intel.com>,
 Hans de Goede <hdegoede@...hat.com>, Mark Gross <markgross@...nel.org>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Jose Abreu <Jose.Abreu@...opsys.com>, "David S . Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Richard Cochran <richardcochran@...il.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>, Andrew Lunn <andrew@...n.ch>,
 Heiner Kallweit <hkallweit1@...il.com>,
 Philipp Zabel <p.zabel@...gutronix.de>, Andrew Halaney
 <ahalaney@...hat.com>, Serge Semin <fancer.lancer@...il.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, platform-driver-x86@...r.kernel.org,
 linux-hwmon@...r.kernel.org, bpf@...r.kernel.org,
 Voon Wei Feng <weifeng.voon@...el.com>,
 Michael Sit Wei Hong <michael.wei.hong.sit@...el.com>,
 Lai Peter Jun Ann <jun.ann.lai@...el.com>,
 Abdul Rahim Faizal <faizal.abdul.rahim@...el.com>
Subject: Re: [PATCH net-next v4 06/11] net: stmmac: resetup XPCS according to
 the new interface mode

On 2/2/2024 4:50 pm, Russell King (Oracle) wrote:
>> Thank you for taking the time to review, got your concerns, and I'll address
>> the following concerns before submitting a new patch series:
>>
>> 1. Remove allow_switch_interface and have the PHY driver fill in
>> phydev->possible_interfaces.
> 
> Yes please.
> 

Hi Russell,

I regret to inform you that I didn't implement everything exactly as 
proposed in the new patch series. My intention was to simplify the series, 
focusing solely on managing SGMII and 2500BASE-X interface mode switching. 
The recommendation to have the PHY driver fill in 
"phydev->possible_interfaces" will be addressed in a separate patch 
submission. I hope this is acceptable.

In the new patch series, I removed "allow_switch_interface" patches. The 
current solution continues to work with PHYs that are C45 and follow the 
legacy path, such as Marvell Alaska 88E2110. For the upcoming patch series, 
I will implement "phydev->possible_interfaces" for C22 and C45 PHYs.

>> 2. Rework on the PCS to have similar implementation with the following patch
>> "net: macb: use .mac_select_pcs() interface"
>> (https://lore.kernel.org/netdev/E1n568J-002SZX-Gr@rmk-PC.armlinux.org.uk/T/).
> 
> mac_select_pcs() is about returning to phylink the PCS that the MAC
> needs to use for the specified interface mode, or NULL if no PCS is
> required, nothing more, nothing less.
> 
> Plase do not copy that mac_select_pcs() implementation - changing the
> "ops" underneath phylink is no longer permitted.
> 

Upon further examination, I discovered that no change is required for the 
"mac_select_pcs()" function; we can still use the same PCS. According to 
the XPCS datasheet, a soft reset is necessary to re-initiate Clause 37 
auto-negotiation when switching to SGMII interface mode. This is the only 
setting required for properly configuring the SGMII interface mode, and 
nothing extra is needed for 2500BASE-X configuration.

In the new patch series, I removed "mac_select_pcs()" related patches and 
added a "xpcs_soft_reset()" patch for the XPCS.