Subject: Re: [PATCH net-next 7/8] net: phy: Add Synopsys DesignWare XPCS MDIO module

From: Russell King - ARM Linux admin <[email-masked]>
Date: Fri, 5 Jun 2020 18:10:34 +0100

Hi Jose,

I just tripped over a bug while grepping for something else and
reading a bit of this driver:

On Mon, Mar 09, 2020 at 09:36:26AM +0100, Jose Abreu wrote:
> +static int xpcs_read_lpa(struct mdio_xpcs_args *xpcs,
> +			 struct phylink_link_state *state)
> +{
> +	int ret;
> +
> +	ret = xpcs_read(xpcs, MDIO_MMD_AN, MDIO_STAT1);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (!(ret & MDIO_AN_STAT1_LPABLE)) {
> +		phylink_clear(state->lp_advertising, Autoneg);
> +		return 0;
> +	}
> +
> +	phylink_set(state->lp_advertising, Autoneg);
> +
> +	/* Clause 73 outcome */
> +	ret = xpcs_read(xpcs, MDIO_MMD_AN, DW_SR_AN_LP_ABL3);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (ret & DW_C73_2500KX)
> +		phylink_set(state->lp_advertising, 2500baseX_Full);
> +
> +	ret = xpcs_read(xpcs, MDIO_MMD_AN, DW_SR_AN_LP_ABL2);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (ret & DW_C73_1000KX)
> +		phylink_set(state->lp_advertising, 1000baseKX_Full);
> +	if (ret & DW_C73_10000KX4)
> +		phylink_set(state->lp_advertising, 10000baseKX4_Full);
> +	if (ret & DW_C73_10000KR)
> +		phylink_set(state->lp_advertising, 10000baseKR_Full);
> +
> +	ret = xpcs_read(xpcs, MDIO_MMD_AN, DW_SR_AN_LP_ABL1);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (ret & DW_C73_PAUSE)
> +		phylink_set(state->lp_advertising, Pause);
> +	if (ret & DW_C73_ASYM_PAUSE)
> +		phylink_set(state->lp_advertising, Asym_Pause);
> +
> +	linkmode_and(state->lp_advertising, state->lp_advertising,
> +		     state->advertising);

This is incorrect - you should not mask the link partner's advertisement
with our advertisement like this; consider the table in 802.3 for
resolving the pause modes, where simply doing a bitwise-and operation
between the two advertisements would severely restrict the resulting
resolution to either symmetric pause or nothing at all.

You want to do this when you resolve the speed, but only _temporarily_
in order to resolve the speed - you do not want to write back the
result to state->lp_advertising.

You may wish to fix that.

Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC for 0.8m (est. 1762m) line in suburbia: sync at 13.1Mbps down 424kbps up

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