netdev - Re: [PATCH net-next v2 0/7] net: stmmac/xpcs: modernise PCS support

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Message-ID: <CA+V-a8taTL1aQ5L1uYfJ405X38953z1FO=X5S54QBqGxLsF5ow@mail.gmail.com>
Date: Fri, 17 Oct 2025 18:00:38 +0100
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>, 
	Giuseppe Cavallaro <peppe.cavallaro@...com>, Jose Abreu <Jose.Abreu@...opsys.com>, 
	Maxime Coquelin <mcoquelin.stm32@...il.com>, Andrew Lunn <andrew@...n.ch>, 
	"David S. Miller" <davem@...emloft.net>, Heiner Kallweit <hkallweit1@...il.com>, 
	Jakub Kicinski <kuba@...nel.org>, Jose Abreu <joabreu@...opsys.com>, 
	linux-arm-kernel@...ts.infradead.org, 
	linux-stm32@...md-mailman.stormreply.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2 0/7] net: stmmac/xpcs: modernise PCS support

Hi,

On Wed, Jan 26, 2022 at 10:32 AM Russell King (Oracle)
<linux@...linux.org.uk> wrote:
>
> Hi,
>
> This series updates xpcs and stmmac for the recent changes to phylink
> to better support split PCS and to get rid of private MAC validation
> functions.
>
> This series is slightly more involved than other conversions as stmmac
> has already had optional proper split PCS support.
>
> The first six patches of this series were originally posted on 16th
> December for CFT, and Wong Vee Khee reported his Intel Elkhart Lake
> setup was fine the first six these. However, no tested-by was given.
>
> The patches:
>
> 1) Provide a function to query the xpcs for the interface modes that
>    are supported.
>
> 2) Populates the MAC capabilities and switches stmmac_validate() to use
>    phylink_get_linkmodes(). We do not use phylink_generic_validate() yet
>    as (a) we do not always have the supported interfaces populated, and
>    (b) the existing code does not restrict based on interface. There
>    should be no functional effect from this patch.
>
> 3) Populates phylink's supported interfaces from the xpcs when the xpcs
>    is configured by firmware and also the firmware configured interface
>    mode. Note: this will restrict stmmac to only supporting these
>    interfaces modes - stmmac maintainers need to verify that this
>    behaviour is acceptable.
>
> 4) stmmac_validate() tail-calls xpcs_validate(), but we don't need it to
>    now that PCS have their own validation method. Convert stmmac and
>    xpcs to use this method instead.
>
> 5) xpcs sets the poll field of phylink_pcs to true, meaning xpcs
>    requires its status to be polled. There is no need to also set the
>    phylink_config.pcs_poll. Remove this.
>
> 6) Switch to phylink_generic_validate(). This is probably the most
>    contravertial change in this patch set as this will cause the MAC to
>    restrict link modes based on the interface mode. From an inspection
>    of the xpcs driver, this should be safe, as XPCS only further
>    restricts the link modes to a subset of these (whether that is
>    correct or not is not an issue I am addressing here.) For
>    implementations that do not use xpcs, this is a more open question
>    and needs feedback from stmmac maintainers.
>
> 7) Convert to use mac_select_pcs() rather than phylink_set_pcs() to set
>    the PCS - the intention is to eventually remove phylink_set_pcs()
>    once there are no more users of this.
>
> v2: fix signoff and temporary warning in patch 4
>
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 147 +++++++---------------
>  drivers/net/pcs/pcs-xpcs.c                        |  41 +++---
>  include/linux/pcs/pcs-xpcs.h                      |   3 +-
>  3 files changed, 73 insertions(+), 118 deletions(-)
>
Although RZ/V2H doesn't have PCS, it tested this on Renesas RZ/V2H EVK
and found no regressions.

Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>

Cheers,
Prabhakar