netdev - Re: [PATCH net-next 1/5] sky2: force receive checksum when using RSS on some hardware

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Date:	Thu, 7 Jul 2011 19:04:46 +0200
From:	Michał Mirosław <mirqus@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 1/5] sky2: force receive checksum when using RSS
 on some hardware

2011/7/7 Stephen Hemminger <shemminger@...tta.com>:
> Found when reviewing the vendor driver. Apparently some chip versions
> require receive checksumming to be enabled in order for RSS to work.
> Rather than silently enabling checksumming which is what the vendor
> driver does, return an error to the user instead.
>
> Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
>
>
> --- a/drivers/net/sky2.c        2011-07-07 08:36:10.748003369 -0700
> +++ b/drivers/net/sky2.c        2011-07-07 08:36:37.372004595 -0700
> @@ -2996,7 +2996,8 @@ static int __devinit sky2_init(struct sk
>                hw->flags = SKY2_HW_GIGABIT
>                        | SKY2_HW_NEWER_PHY
>                        | SKY2_HW_NEW_LE
> -                       | SKY2_HW_ADV_POWER_CTL;
> +                       | SKY2_HW_ADV_POWER_CTL
> +                       | SKY2_HW_RSS_CHKSUM;
>
>                /* New transmit checksum */
>                if (hw->chip_rev != CHIP_REV_YU_EX_B0)
> @@ -3024,7 +3025,7 @@ static int __devinit sky2_init(struct sk
>
>                /* The workaround for status conflicts VLAN tag detection. */
>                if (hw->chip_rev == CHIP_REV_YU_FE2_A0)
> -                       hw->flags |= SKY2_HW_VLAN_BROKEN;
> +                       hw->flags |= SKY2_HW_VLAN_BROKEN | SKY2_HW_RSS_CHKSUM;
>                break;
>
>        case CHIP_ID_YUKON_SUPR:
> @@ -3033,6 +3034,9 @@ static int __devinit sky2_init(struct sk
>                        | SKY2_HW_NEW_LE
>                        | SKY2_HW_AUTO_TX_SUM
>                        | SKY2_HW_ADV_POWER_CTL;
> +
> +               if (hw->chip_rev == CHIP_REV_YU_SU_A0)
> +                       hw->flags |= SKY2_HW_RSS_CHKSUM;
>                break;
>
>        case CHIP_ID_YUKON_UL_2:
> @@ -4187,6 +4191,11 @@ static int sky2_set_features(struct net_
>        struct sky2_port *sky2 = netdev_priv(dev);
>        u32 changed = dev->features ^ features;
>
> +       /* Some hardware requires receive checksum for RSS to work. */
> +       if ( (features & (NETIF_F_RXHASH|NETIF_F_RXCSUM)) == NETIF_F_RXHASH &&
> +            (sky2->hw->flags & SKY2_HW_RSS_CHKSUM))
> +               return -EINVAL;
> +
>        if (changed & NETIF_F_RXCSUM) {
>                u32 on = features & NETIF_F_RXCSUM;
>                sky2_write32(sky2->hw, Q_ADDR(rxqaddr[sky2->port], Q_CSR),

Nah. This won't work as the error is not passed to user (except via
dmesg) as there is no way to do it. Failing ndo_set_features() without
updating dev->features will also prevent other unrelated changes to
features set.

This should either force RXCSUM when RXHASH is on or disable RXHASH
when RXCSUM is off (both in sky2_fix_features()). Or maybe enable
RXCSUM with RXHASH but ignore hardware-computed checksum when it's not
requested.

Best Regards,
Michał Mirosław
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