netdev - Re: [PATCH net v5 1/3] net: phylink: add phylink_expects

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Date:   Wed, 12 Apr 2023 10:38:12 +0200
From:   Maxime Chevallier <maxime.chevallier@...tlin.com>
To:     Michael Sit Wei Hong <michael.wei.hong.sit@...el.com>
Cc:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...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>,
        Ong Boon Leong <boon.leong.ong@...el.com>,
        netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux@...linux.org.uk, hkallweit1@...il.com, andrew@...n.ch,
        Looi Hong Aun <hong.aun.looi@...el.com>,
        Voon Weifeng <weifeng.voon@...el.com>,
        Lai Peter Jun Ann <peter.jun.ann.lai@...el.com>,
        "alexis.lothore@...tlin.com" <alexis.lothore@...tlin.com>
Subject: Re: [PATCH net v5 1/3] net: phylink: add phylink_expects_phy()
 method

Hello everyone,

On Thu, 30 Mar 2023 17:14:02 +0800
Michael Sit Wei Hong <michael.wei.hong.sit@...el.com> wrote:

> Provide phylink_expects_phy() to allow MAC drivers to check if it
> is expecting a PHY to attach to. Since fixed-linked setups do not
> need to attach to a PHY.
> 
> Provides a boolean value as to if the MAC should expect a PHY.
> Returns true if a PHY is expected.

I'm currently working on the TSE rework for dwmac_socfpga, and I
noticed one regression since this patch, when using an SFP, see details
below :

> Reviewed-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> Signed-off-by: Michael Sit Wei Hong <michael.wei.hong.sit@...el.com>
> ---
>  drivers/net/phy/phylink.c | 19 +++++++++++++++++++
>  include/linux/phylink.h   |  1 +
>  2 files changed, 20 insertions(+)
> 
> diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
> index 1a2f074685fa..30c166b33468 100644
> --- a/drivers/net/phy/phylink.c
> +++ b/drivers/net/phy/phylink.c
> @@ -1586,6 +1586,25 @@ void phylink_destroy(struct phylink *pl)
>  }
>  EXPORT_SYMBOL_GPL(phylink_destroy);
>  
> +/**
> + * phylink_expects_phy() - Determine if phylink expects a phy to be
> attached
> + * @pl: a pointer to a &struct phylink returned from phylink_create()
> + *
> + * When using fixed-link mode, or in-band mode with 1000base-X or
> 2500base-X,
> + * no PHY is needed.
> + *
> + * Returns true if phylink will be expecting a PHY.
> + */
> +bool phylink_expects_phy(struct phylink *pl)
> +{
> +	if (pl->cfg_link_an_mode == MLO_AN_FIXED ||
> +	    (pl->cfg_link_an_mode == MLO_AN_INBAND &&
> +	     phy_interface_mode_is_8023z(pl->link_config.interface)))

From the discussion, at one point Russell mentionned [1] :
"If there's a sfp bus, then we don't expect a PHY from the MAC driver
(as there can only be one PHY attached), and as phylink_expects_phy()
is for the MAC driver to use, we should be returning false if
pl->sfp_bus != NULL."

This makes sense and indeed adding the relevant check solves the issue.

Am I correct in assuming this was an unintentional omission from this
patch, or was the pl->sfp_bus check dropped on purpose ?

> +		return false;
> +	return true;
> +}
> +EXPORT_SYMBOL_GPL(phylink_expects_phy);

Thanks,

Maxime

[1] :
https://lore.kernel.org/netdev/ZCQJWcdfmualIjvX@shell.armlinux.org.uk/