Re: [PATCH net-next v2 2/2] net: phy: Add driver for Motorcomm yt8821 2.5G ethernet phy

From: Russell King (Oracle)
Date: Sat Aug 17 2024 - 07:36:56 EST


On Thu, Aug 15, 2024 at 11:09:55PM -0700, Frank Sae wrote:
> +static int yt8821_get_rate_matching(struct phy_device *phydev,
> + phy_interface_t iface)
> +{
> + int val;
> +
> + val = ytphy_read_ext_with_lock(phydev, YT8521_CHIP_CONFIG_REG);
> + if (val < 0)
> + return val;
> +
> + if (FIELD_GET(YT8521_CCR_MODE_SEL_MASK, val) ==
> + YT8821_CHIP_MODE_FORCE_BX2500)
> + return RATE_MATCH_PAUSE;

Does this device do rate matching for _any_ interface mode if it has
this bit set - because that's what you're saying here by not testing
"iface". From what I understand from your previous posting which
included a DT update, this only applies when 2500base-X is being
used as the interface mode.

> +static int yt8821_aneg_done(struct phy_device *phydev)
> +{
> + int link;
> +
> + link = yt8521_aneg_done_paged(phydev, YT8521_RSSR_UTP_SPACE);
> +
> + return link;
> +}

Why not just:

return yt8521_aneg_done_paged(phydev, YT8521_RSSR_UTP_SPACE);

?

> +/**
> + * yt8821_config_init() - phy initializatioin
> + * @phydev: a pointer to a &struct phy_device
> + *
> + * Returns: 0 or negative errno code
> + */
> +static int yt8821_config_init(struct phy_device *phydev)
> +{
> + u8 mode = YT8821_CHIP_MODE_AUTO_BX2500_SGMII;
> + int ret;
> + u16 set;
> +
> + if (phydev->interface == PHY_INTERFACE_MODE_2500BASEX)
> + mode = YT8821_CHIP_MODE_FORCE_BX2500;

Hmm, I think this is tying us into situations we don't want. What if the
host supports 2500base-X and SGMII, but does not support pause (for
example, Marvell PP2 based hosts.) In that situation, we don't want to
lock-in to using pause based rate adaption, which I fear will become
a behaviour that would be risky to change later on.

> +
> + set = FIELD_PREP(YT8521_CCR_MODE_SEL_MASK, mode);
> + ret = ytphy_modify_ext_with_lock(phydev,
> + YT8521_CHIP_CONFIG_REG,
> + YT8521_CCR_MODE_SEL_MASK,
> + set);
> + if (ret < 0)
> + return ret;
> +
> + if (mode == YT8821_CHIP_MODE_AUTO_BX2500_SGMII) {
> + __set_bit(PHY_INTERFACE_MODE_2500BASEX,
> + phydev->possible_interfaces);
> + __set_bit(PHY_INTERFACE_MODE_SGMII,
> + phydev->possible_interfaces);
> +
> + phydev->rate_matching = RATE_MATCH_NONE;
> + } else if (mode == YT8821_CHIP_MODE_FORCE_BX2500) {

__set_bit(PHY_INTERFACE_MODE_2500BASEX,
phydev->possible_interfaces);

so that phylink knows you're only going to be using a single interface
mode. Even better, since this is always supported, move it out of these
if() statements?


Also, it would be nice to have phydev->supported_interfaces populated
(which has to be done when the PHY is probed) so that phylink knows
before connecting with the PHY which interface modes are supported by
the PHY. (Andrew - please can we make this a condition for any new PHYs
supported by phylib in the future?)

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