Subject: RE: [PATCH v4 bpf-next 01/10] ice: compress branches in ice_set_features()

From: John Fastabend <[email-masked]>
Date: Fri, 17 Jun 2022 18:46:35 -0700

Maciej Fijalkowski wrote:
> Instead of rather verbose comparison of current netdev->features bits vs
> the incoming ones from user, let us compress them by a helper features
> set that will be the result of netdev->features XOR features. This way,
> current, extensive branches:
> 
> 	if (features & NETIF_F_BIT && !(netdev->features & NETIF_F_BIT))
> 		set_feature(true);
> 	else if (!(features & NETIF_F_BIT) && netdev->features & NETIF_F_BIT)
> 		set_feature(false);
> 
> can become:
> 
> 	netdev_features_t changed = netdev->features ^ features;
> 
> 	if (changed & NETIF_F_BIT)
> 		set_feature(!!(features & NETIF_F_BIT));
> 
> This is nothing new as currently several other drivers use this
> approach, which I find much more convenient.

Looks good couple nits below. Up to you if you want to follow through
on them or not I don't have a strong opinion. For what its worth the
other intel drivers also do the 'netdev->features ^ features'
assignment.

Acked-by: John Fastabend <[email-masked]>

> 
> CC: Alexandr Lobakin <[email-masked]>
> Signed-off-by: Maciej Fijalkowski <[email-masked]>
> ---
>  drivers/net/ethernet/intel/ice/ice_main.c | 40 +++++++++++------------
>  1 file changed, 19 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_main.c b/drivers/net/ethernet/intel/ice/ice_main.c
> index e1cae253412c..23d1b1fc39fb 100644
> --- a/drivers/net/ethernet/intel/ice/ice_main.c
> +++ b/drivers/net/ethernet/intel/ice/ice_main.c
> @@ -5910,44 +5910,41 @@ ice_set_vlan_features(struct net_device *netdev, netdev_features_t features)
>  static int
>  ice_set_features(struct net_device *netdev, netdev_features_t features)
>  {
> +	netdev_features_t changed = netdev->features ^ features;
>  	struct ice_netdev_priv *np = netdev_priv(netdev);
>  	struct ice_vsi *vsi = np->vsi;
>  	struct ice_pf *pf = vsi->back;
>  	int ret = 0;
>  
>  	/* Don't set any netdev advanced features with device in Safe Mode */
> -	if (ice_is_safe_mode(vsi->back)) {
> -		dev_err(ice_pf_to_dev(vsi->back), "Device is in Safe Mode - not enabling advanced netdev features\n");
> +	if (ice_is_safe_mode(pf)) {
> +		dev_err(ice_pf_to_dev(vsi->back),

bit of nitpicking but if you use pf in the 'if' above why not use it here
as well and save a few keys. Also matches below then.

> +			"Device is in Safe Mode - not enabling advanced netdev features\n");
>  		return ret;
>  	}
>  
>  	/* Do not change setting during reset */
>  	if (ice_is_reset_in_progress(pf->state)) {
> -		dev_err(ice_pf_to_dev(vsi->back), "Device is resetting, changing advanced netdev features temporarily unavailable.\n");
> +		dev_err(ice_pf_to_dev(pf),
> +			"Device is resetting, changing advanced netdev features temporarily unavailable.\n");
>  		return -EBUSY;
>  	}
>  

[...]

> @@ -5956,11 +5953,12 @@ ice_set_features(struct net_device *netdev, netdev_features_t features)
>  		return -EACCES;
>  	}
>  
> -	if ((features & NETIF_F_HW_TC) &&
> -	    !(netdev->features & NETIF_F_HW_TC))
> -		set_bit(ICE_FLAG_CLS_FLOWER, pf->flags);
> -	else
> -		clear_bit(ICE_FLAG_CLS_FLOWER, pf->flags);
> +	if (changed & NETIF_F_HW_TC) {
> +		bool ena = !!(features & NETIF_F_HW_TC);
> +
> +		ena ? set_bit(ICE_FLAG_CLS_FLOWER, pf->flags) :
> +		      clear_bit(ICE_FLAG_CLS_FLOWER, pf->flags);
> +	}

Just a note you changed the logic slightly here. Above you always
clear the bit. But, it looks like it doesn't matter caveat being
I don't know what might happen in hardware.

>  	return 0;
>  }
> -- 
> 2.27.0