Subject: Re: [PATCH v2 net-next 1/9] net: enetc: fix MAC Merge layer remaining enabled until a link down event

From: Simon Horman <[email-masked]>
Date: Thu, 20 Apr 2023 16:22:04 +0200

On Tue, Apr 18, 2023 at 02:14:51PM +0300, Vladimir Oltean wrote:
> Current enetc_set_mm() is designed to set the priv->active_offloads bit
> ENETC_F_QBU for enetc_mm_link_state_update() to act on, but if the link
> is already up, it modifies the ENETC_MMCSR_ME ("Merge Enable") bit
> directly.
> 
> The problem is that it only *sets* ENETC_MMCSR_ME if the link is up, it
> doesn't *clear* it if needed. So subsequent enetc_get_mm() calls still
> see tx-enabled as true, up until a link down event, which is when
> enetc_mm_link_state_update() will get called.
> 
> This is not a functional issue as far as I can assess. It has only come
> up because I'd like to uphold a simple API rule in core ethtool code:
> the pMAC cannot be disabled if TX is going to be enabled. Currently,
> the fact that TX remains enabled for longer than expected (after the
> enetc_set_mm() call that disables it) is going to violate that rule,
> which is how it was caught.
> 
> Signed-off-by: Vladimir Oltean <[email-masked]>

Reviewed-by: Simon Horman <[email-masked]>

> ---
> v1->v2: none
> 
>  drivers/net/ethernet/freescale/enetc/enetc_ethtool.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/enetc/enetc_ethtool.c b/drivers/net/ethernet/freescale/enetc/enetc_ethtool.c
> index 838750a03cf6..ee1ea71fe79e 100644
> --- a/drivers/net/ethernet/freescale/enetc/enetc_ethtool.c
> +++ b/drivers/net/ethernet/freescale/enetc/enetc_ethtool.c
> @@ -1041,10 +1041,13 @@ static int enetc_set_mm(struct net_device *ndev, struct ethtool_mm_cfg *cfg,
>  	else
>  		priv->active_offloads &= ~ENETC_F_QBU;
>  
> -	/* If link is up, enable MAC Merge right away */
> -	if (!!(priv->active_offloads & ENETC_F_QBU) &&
> -	    !(val & ENETC_MMCSR_LINK_FAIL))
> -		val |= ENETC_MMCSR_ME;
> +	/* If link is up, enable/disable MAC Merge right away */
> +	if (!(val & ENETC_MMCSR_LINK_FAIL)) {
> +		if (!!(priv->active_offloads & ENETC_F_QBU))

nit: The !!() seems unnecessary,
     I wonder if it can be written in a simpler way as:

		if (priv->active_offloads & ENETC_F_QBU)

> +			val |= ENETC_MMCSR_ME;
> +		else
> +			val &= ~ENETC_MMCSR_ME;
> +	}
>  
>  	val &= ~ENETC_MMCSR_VT_MASK;
>  	val |= ENETC_MMCSR_VT(cfg->verify_time);
> -- 
> 2.34.1
>