netdev - Re: [PATCH] net: macb: reject unsupported rgmii delays

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Date:   Wed, 17 Jun 2020 12:57:23 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Helmut Grohne <helmut.grohne@...enta.de>
Cc:     Nicolas Ferre <nicolas.ferre@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: macb: reject unsupported rgmii delays

Hi Helmut,

On Tue, 16 Jun 2020 at 11:00, Helmut Grohne <helmut.grohne@...enta.de> wrote:
>
> The macb driver does not support configuring rgmii delays. At least for
> the Zynq GEM, delays are not supported by the hardware at all. However,
> the driver happily accepts and ignores any such delays.
>
> When operating in a mac to phy connection, the delay setting applies to
> the phy. Since the MAC does not support delays, the phy must provide
> them and the only supported mode is rgmii-id.  However, in a fixed mac
> to mac connection, the delay applies to the mac itself. Therefore the
> only supported rgmii mode is rgmii.
>
> Link: https://lore.kernel.org/netdev/20200610081236.GA31659@laureti-dev/
> Signed-off-by: Helmut Grohne <helmut.grohne@...enta.de>
> ---
>  drivers/net/ethernet/cadence/macb_main.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index 5b9d7c60eebc..bee5bf65e8b3 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -514,7 +514,7 @@ static void macb_validate(struct phylink_config *config,
>             state->interface != PHY_INTERFACE_MODE_RMII &&
>             state->interface != PHY_INTERFACE_MODE_GMII &&
>             state->interface != PHY_INTERFACE_MODE_SGMII &&
> -           !phy_interface_mode_is_rgmii(state->interface)) {
> +           state->interface != PHY_INTERFACE_MODE_RGMII_ID) {

I don't think this change is correct though?
What if there were PCB traces in place, for whatever reason? Then the
driver would need to accept a phy with rgmii-txid, rgmii-rxid or
rgmii.

>                 bitmap_zero(supported, __ETHTOOL_LINK_MODE_MASK_NBITS);
>                 return;
>         }
> @@ -694,6 +694,13 @@ static int macb_phylink_connect(struct macb *bp)
>         struct phy_device *phydev;
>         int ret;
>
> +       if (of_phy_is_fixed_link(dn) &&
> +           phy_interface_mode_is_rgmii(bp->phy_interface) &&
> +           bp->phy_interface != PHY_INTERFACE_MODE_RGMII) {
> +               netdev_err(dev, "RGMII delays are not supported\n");
> +               return -EINVAL;
> +       }
> +

Have you checked that this doesn't break any existing in-tree users?

>         if (dn)
>                 ret = phylink_of_phy_connect(bp->phylink, dn, 0);
>
> --
> 2.20.1
>

Thanks,
-Vladimir