Date: Tue, 20 Feb 2024 18:05:57 -0500
From: Sean Anderson <sean.anderson@...o.com>
To: Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Madalin Bucur <madalin.bucur@....com>,
 Russell King <linux@...linux.org.uk>,
 Zachary Goldstein <zachary.goldstein@...current-rt.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: dpaa: fman_memac: accept phy-interface-type =
 "10gbase-r" in the device tree

On 2/20/24 17:34, Vladimir Oltean wrote:
> Since commit 5d93cfcf7360 ("net: dpaa: Convert to phylink"), we support
> the "10gbase-r" phy-mode through a driver-based conversion of "xgmii",
> but we still don't actually support it when the device tree specifies
> "10gbase-r" proper.
>
> This is because boards such as LS1046A-RDB do not define pcs-handle-names
> (for whatever reason) in the ethernet@...00 device tree node, and the
> code enters through this code path:
>
>       err = of_property_match_string(mac_node, "pcs-handle-names", "xfi");
>       // code takes neither branch and falls through
>       if (err >= 0) {
>               (...)
>       } else if (err != -EINVAL && err != -ENODATA) {
>               goto _return_fm_mac_free;
>       }
>
>       (...)
>
>       /* For compatibility, if pcs-handle-names is missing, we assume this
>        * phy is the first one in pcsphy-handle
>        */
>       err = of_property_match_string(mac_node, "pcs-handle-names", "sgmii");
>       if (err == -EINVAL || err == -ENODATA)
>               pcs = memac_pcs_create(mac_node, 0); // code takes this branch
>       else if (err < 0)
>               goto _return_fm_mac_free;
>       else
>               pcs = memac_pcs_create(mac_node, err);
>
>       // A default PCS is created and saved in "pcs"
>
>       // This determination fails and mistakenly saves the default PCS
>       // memac->sgmii_pcs instead of memac->xfi_pcs, because at this
>       // stage, mac_dev->phy_if == PHY_INTERFACE_MODE_10GBASER.
>       if (err && mac_dev->phy_if == PHY_INTERFACE_MODE_XGMII)
>               memac->xfi_pcs = pcs;
>       else
>               memac->sgmii_pcs = pcs;
>
> In other words, in the absence of pcs-handle-names, the default
> xfi_pcs assignment logic only works when in the device tree we have
> PHY_INTERFACE_MODE_XGMII.
>
> By reversing the order between the fallback xfi_pcs assignment and the
> "xgmii" overwrite with "10gbase-r", we are able to support both values
> in the device tree, with identical behavior.
>
> Currently, it is impossible to make the s/xgmii/10gbase-r/ device tree
> conversion, because it would break forward compatibility (new device
> tree with old kernel). The only way to modify existing device trees to
> phy-interface-mode = "10gbase-r" is to fix stable kernels to accept this
> value and handle it properly.
>
> One reason why the conversion is desirable is because with pre-phylink
> kernels, the Aquantia PHY driver used to warn about the improper use
> of PHY_INTERFACE_MODE_XGMII [1]. It is best to have a single (latest)
> device tree that works with all supported stable kernel versions.
>
> Note that the blamed commit does not constitute a regression per se.
> Older stable kernels like 6.1 still do not work with "10gbase-r", but
> for a different reason. That is a battle for another time.
>
> [1] https://cas5-0-urlprotect.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2flore.kernel.org%2fnetdev%2f20240214%2dls1046%2ddts%2duse%2d10gbase%2dr%2dv1%2d1%2d8c2d68547393%40concurrent%2drt.com%2f&umid=9e7ee942-44ce-4bdd-a3c5-0de04f0ee53f&auth=d807158c60b7d2502abde8a2fc01f40662980862-d5a8b704cd04b796a2aa2a861dad36f29073bce5
>
> Fixes: 5d93cfcf7360 ("net: dpaa: Convert to phylink")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
>  .../net/ethernet/freescale/fman/fman_memac.c   | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/ethernet/freescale/fman/fman_memac.c b/drivers/net/ethernet/freescale/fman/fman_memac.c
> index e30bf75b1d48..0996759907a8 100644
> --- a/drivers/net/ethernet/freescale/fman/fman_memac.c
> +++ b/drivers/net/ethernet/freescale/fman/fman_memac.c
> @@ -1076,6 +1076,14 @@ int memac_initialization(struct mac_device *mac_dev,
>       unsigned long            capabilities;
>       unsigned long           *supported;
>
> +     /* The internal connection to the serdes is XGMII, but this isn't
> +      * really correct for the phy mode (which is the external connection).
> +      * However, this is how all older device trees say that they want
> +      * 10GBASE-R (aka XFI), so just convert it for them.
> +      */
> +     if (mac_dev->phy_if == PHY_INTERFACE_MODE_XGMII)
> +             mac_dev->phy_if = PHY_INTERFACE_MODE_10GBASER;
> +
>       mac_dev->phylink_ops            = &memac_mac_ops;
>       mac_dev->set_promisc            = memac_set_promiscuous;
>       mac_dev->change_addr            = memac_modify_mac_address;
> @@ -1142,7 +1150,7 @@ int memac_initialization(struct mac_device *mac_dev,
>        * (and therefore that xfi_pcs cannot be set). If we are defaulting to
>        * XGMII, assume this is for XFI. Otherwise, assume it is for SGMII.
>        */
> -     if (err && mac_dev->phy_if == PHY_INTERFACE_MODE_XGMII)
> +     if (err && mac_dev->phy_if == PHY_INTERFACE_MODE_10GBASER)
>               memac->xfi_pcs = pcs;
>       else
>               memac->sgmii_pcs = pcs;
> @@ -1156,14 +1164,6 @@ int memac_initialization(struct mac_device *mac_dev,
>               goto _return_fm_mac_free;
>       }
>
> -     /* The internal connection to the serdes is XGMII, but this isn't
> -      * really correct for the phy mode (which is the external connection).
> -      * However, this is how all older device trees say that they want
> -      * 10GBASE-R (aka XFI), so just convert it for them.
> -      */
> -     if (mac_dev->phy_if == PHY_INTERFACE_MODE_XGMII)
> -             mac_dev->phy_if = PHY_INTERFACE_MODE_10GBASER;
> -
>       /* TODO: The following interface modes are supported by (some) hardware
>        * but not by this driver:
>        * - 1000BASE-KX


Reviewed-by: Sean Anderson <sean.anderson@...o.com>

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