Date:   Mon, 20 Feb 2023 02:11:11 +0000
From:   Wei Fang <wei.fang@....com>
To:     Richard Weinberger <richard@....at>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        dl-linux-imx <linux-imx@....com>,
        Clark Wang <xiaoning.wang@....com>,
        Shenwei Wang <shenwei.wang@....com>
Subject: RE: [PATCH] [RFC] net: fec: Allow turning off IRQ coalescing

> -----Original Message-----
> From: Richard Weinberger <richard@....at>
> Sent: 2023年2月19日 5:41
> To: netdev@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org; pabeni@...hat.com; kuba@...nel.org;
> edumazet@...gle.com; davem@...emloft.net; dl-linux-imx
> <linux-imx@....com>; Clark Wang <xiaoning.wang@....com>; Shenwei
> Wang <shenwei.wang@....com>; Wei Fang <wei.fang@....com>; Richard
> Weinberger <richard@....at>
> Subject: [PATCH] [RFC] net: fec: Allow turning off IRQ coalescing
> 
> Setting tx/rx-frames or tx/rx-usecs to zero is currently possible but
> has no effect.
> Also IRQ coalescing is always enabled on supported hardware.
> 
> This is confusing and causes users to believe that they have successfully
> disabled IRQ coalescing by setting tx/rx-frames and tx/rx-usecs to zero.
> 
> With this change applied it is possible to disable IRQ coalescing by
> configuring both tx/rx-frames and tx/rx-usecs to zero.
> 
> Setting only one value to zero is still not possible as the hardware
> does not support it.
> In this case ethtool will face -EINVAL.
> 
> Signed-off-by: Richard Weinberger <richard@....at>
> ---
>  drivers/net/ethernet/freescale/fec_main.c | 73 ++++++++++++++++-------
>  1 file changed, 50 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/fec_main.c
> b/drivers/net/ethernet/freescale/fec_main.c
> index 2341597408d1..cc3c5e09e02f 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -74,7 +74,7 @@
>  #include "fec.h"
> 
>  static void set_multicast_list(struct net_device *ndev);
> -static void fec_enet_itr_coal_set(struct net_device *ndev);
> +static int fec_enet_itr_coal_set(struct net_device *ndev);
> 
>  #define DRIVER_NAME	"fec"
> 
> @@ -1217,7 +1217,7 @@ fec_restart(struct net_device *ndev)
> 
>  	/* Init the interrupt coalescing */
>  	if (fep->quirks & FEC_QUIRK_HAS_COALESCE)
> -		fec_enet_itr_coal_set(ndev);
> +		WARN_ON_ONCE(fec_enet_itr_coal_set(ndev));
>  }
> 
>  static int fec_enet_ipc_handle_init(struct fec_enet_private *fep)
> @@ -2867,30 +2867,57 @@ static int fec_enet_us_to_itr_clock(struct
> net_device *ndev, int us)
>  }
> 
>  /* Set threshold for interrupt coalescing */
> -static void fec_enet_itr_coal_set(struct net_device *ndev)
> +static int fec_enet_itr_coal_set(struct net_device *ndev)
>  {
> +	bool disable_rx_itr = false, disable_tx_itr = false;
>  	struct fec_enet_private *fep = netdev_priv(ndev);
disable_rx_itr should be defined below fep to follow the style of the reverse Christmas tree.

> -	int rx_itr, tx_itr;
> +	struct device *dev = &fep->pdev->dev;
> +	int rx_itr = 0, tx_itr = 0;
> 
> -	/* Must be greater than zero to avoid unpredictable behavior */
> -	if (!fep->rx_time_itr || !fep->rx_pkts_itr ||
> -	    !fep->tx_time_itr || !fep->tx_pkts_itr)
> -		return;
> +	if (!fep->rx_time_itr || !fep->rx_pkts_itr) {
> +		if (fep->rx_time_itr || fep->rx_pkts_itr) {

I think the below should be better:
if (!!fep->rx_time_itr == ! fep->rx_pkts_itr)

> +			dev_warn(dev, "Rx coalesced frames and usec have to be "
> +				      "both positive or both zero to disable Rx "
> +				      "coalescence completely\n");
> +			return -EINVAL;
> +		}
> 
> -	/* Select enet system clock as Interrupt Coalescing
> -	 * timer Clock Source
> -	 */
> -	rx_itr = FEC_ITR_CLK_SEL;
> -	tx_itr = FEC_ITR_CLK_SEL;
> +		disable_rx_itr = true;
> +	}
> 
> -	/* set ICFT and ICTT */
> -	rx_itr |= FEC_ITR_ICFT(fep->rx_pkts_itr);
> -	rx_itr |= FEC_ITR_ICTT(fec_enet_us_to_itr_clock(ndev, fep->rx_time_itr));
> -	tx_itr |= FEC_ITR_ICFT(fep->tx_pkts_itr);
> -	tx_itr |= FEC_ITR_ICTT(fec_enet_us_to_itr_clock(ndev, fep->tx_time_itr));
> +	if (!fep->tx_time_itr || !fep->tx_pkts_itr) {
> +		if (fep->tx_time_itr || fep->tx_pkts_itr) {

Same as above.

> +			dev_warn(dev, "Tx coalesced frames and usec have to be "
> +				      "both positive or both zero to disable Tx "
> +				      "coalescence completely\n");
> +			return -EINVAL;
> +		}
> +
> +		disable_tx_itr = true;
> +	}
> +
> +	if (!disable_rx_itr) {
> +		/* Select enet system clock as Interrupt Coalescing
> +		 * timer Clock Source
> +		 */
> +		rx_itr = FEC_ITR_CLK_SEL;
> +
> +		/* set ICFT and ICTT */
> +		rx_itr |= FEC_ITR_ICFT(fep->rx_pkts_itr);
> +		rx_itr |= FEC_ITR_ICTT(fec_enet_us_to_itr_clock(ndev,
> fep->rx_time_itr));
> +
> +		rx_itr |= FEC_ITR_EN;
> +	}
> +
> +	if (!disable_tx_itr) {
> +		tx_itr = FEC_ITR_CLK_SEL;
> +
> +		tx_itr |= FEC_ITR_ICFT(fep->tx_pkts_itr);
> +		tx_itr |= FEC_ITR_ICTT(fec_enet_us_to_itr_clock(ndev,
> fep->tx_time_itr));
> +
> +		tx_itr |= FEC_ITR_EN;
> +	}
> 
> -	rx_itr |= FEC_ITR_EN;
> -	tx_itr |= FEC_ITR_EN;
> 
>  	writel(tx_itr, fep->hwp + FEC_TXIC0);
>  	writel(rx_itr, fep->hwp + FEC_RXIC0);
> @@ -2900,6 +2927,8 @@ static void fec_enet_itr_coal_set(struct net_device
> *ndev)
>  		writel(tx_itr, fep->hwp + FEC_TXIC2);
>  		writel(rx_itr, fep->hwp + FEC_RXIC2);
>  	}
> +
> +	return 0;
>  }
> 
>  static int fec_enet_get_coalesce(struct net_device *ndev,
> @@ -2961,9 +2990,7 @@ static int fec_enet_set_coalesce(struct net_device
> *ndev,
>  	fep->tx_time_itr = ec->tx_coalesce_usecs;
>  	fep->tx_pkts_itr = ec->tx_max_coalesced_frames;
> 
> -	fec_enet_itr_coal_set(ndev);
> -
> -	return 0;
> +	return fec_enet_itr_coal_set(ndev);
>  }
> 
>  static int fec_enet_get_tunable(struct net_device *netdev,
> --
> 2.26.2

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