netdev - Re: [PATCH net] net: dpaa2-mac: Get serdes only for backplane links

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Date:   Fri, 30 Dec 2022 15:32:24 +0200
From:   Ioana Ciornei <ioana.ciornei@....com>
To:     Sean Anderson <sean.anderson@...o.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net] net: dpaa2-mac: Get serdes only for backplane links

Hi Sean,

On Tue, Dec 27, 2022 at 06:09:18PM -0500, Sean Anderson wrote:
> When commenting on what would become commit 085f1776fa03 ("net: dpaa2-mac:
> add backplane link mode support"), Ioana Ciornei said [1]:
> 
> > ...DPMACs in TYPE_BACKPLANE can have both their PCS and SerDes managed
> > by Linux (since the firmware is not touching these). That being said,
> > DPMACs in TYPE_PHY (the type that is already supported in dpaa2-mac) can
> > also have their PCS managed by Linux (no interraction from the
> > firmware's part with the PCS, just the SerDes).
> 
> This implies that Linux only manages the SerDes when the link type is
> backplane. From my testing, the link fails to come up when the link type is
> phy, but does come up when it is backplane. Modify the condition in
> dpaa2_mac_connect to reflect this, moving the existing conditions to more
> appropriate places.
> 

What interface mode, firmware version etc are you testing on LS1088A?
Are you using the SerDes phy driver?

> [1] https://lore.kernel.org/netdev/20210120221900.i6esmk6uadgqpdtu@skbuf/
> 
> Fixes: f978fe85b8d1 ("dpaa2-mac: configure the SerDes phy on a protocol change")
> Signed-off-by: Sean Anderson <sean.anderson@...o.com>
> ---
> I tested this on an LS1088ARDB. I would appreciate if someone could
> verify that this doesn't break anything for the LX2160A.

I will test on a LX2160A but no sooner than next Tuesday. Sorry.

> 
>  drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c b/drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c
> index c886f33f8c6f..0693d3623a76 100644
> --- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c
> +++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c
> @@ -179,9 +179,13 @@ static void dpaa2_mac_config(struct phylink_config *config, unsigned int mode,
>  	if (err)
>  		netdev_err(mac->net_dev,  "dpmac_set_protocol() = %d\n", err);
>  
> -	err = phy_set_mode_ext(mac->serdes_phy, PHY_MODE_ETHERNET, state->interface);
> -	if (err)
> -		netdev_err(mac->net_dev, "phy_set_mode_ext() = %d\n", err);
> +	if (!phy_interface_mode_is_rgmii(mode)) {
> +		err = phy_set_mode_ext(mac->serdes_phy, PHY_MODE_ETHERNET,
> +				       state->interface);
> +		if (err)
> +			netdev_err(mac->net_dev, "phy_set_mode_ext() = %d\n",
> +				   err);
> +	}
>  }

This check is not necessary. Just above the snippet shown here is:

	if (!mac->serdes_phy)
		return;

And the 'serdes_phy' is only setup if the interface mode is not a rgmii.
	if (mac->features & DPAA2_MAC_FEATURE_PROTOCOL_CHANGE &&
	    !phy_interface_mode_is_rgmii(mac->if_mode) &&
	    is_of_node(dpmac_node)) {
		serdes_phy = of_phy_get(to_of_node(dpmac_node), NULL);
		
		if (serdes_phy == ERR_PTR(-ENODEV))
			serdes_phy = NULL;
		else if (IS_ERR(serdes_phy))
			return PTR_ERR(serdes_phy);
		else
			phy_init(serdes_phy);
	}
	mac->serdes_phy = serdes_phy;



>  
>  static void dpaa2_mac_link_up(struct phylink_config *config,
> @@ -317,7 +321,8 @@ static void dpaa2_mac_set_supported_interfaces(struct dpaa2_mac *mac)
>  		}
>  	}
>  
> -	if (!mac->serdes_phy)
> +	if (!(mac->features & !DPAA2_MAC_FEATURE_PROTOCOL_CHANGE) ||
> +	    !mac->serdes_phy)
>  		return;
>  
>  	/* In case we have access to the SerDes phy/lane, then ask the SerDes
> @@ -377,8 +382,7 @@ int dpaa2_mac_connect(struct dpaa2_mac *mac)
>  		return -EINVAL;
>  	mac->if_mode = err;
>  
> -	if (mac->features & DPAA2_MAC_FEATURE_PROTOCOL_CHANGE &&
> -	    !phy_interface_mode_is_rgmii(mac->if_mode) &&
> +	if (mac->attr.link_type == DPMAC_LINK_TYPE_BACKPLANE &&
>  	    is_of_node(dpmac_node)) {
>  		serdes_phy = of_phy_get(to_of_node(dpmac_node), NULL);
>  

If the goal is to restrict the serdes_phy setup only if in _BACKPLANE
mode, then why not just add another restriction here directly?

What I mean is not to remove any checks from this if statement but
rather add another one. And this would be the only change needed.


Ioana