[PATCH 2/2] netdev/fec: fix performance impact from mdio poll operation

[Andy Whitcroft]

On Thu, Apr 08, 2010 at 02:44:59PM +0800, Bryan Wu wrote:
> BugLink: http://bugs.launchpad.net/bugs/546649
> BugLink: http://bugs.launchpad.net/bugs/457878
> 
> After introducing phylib supporting, users experienced performace drop. That is
> because of the mdio polling operation of phylib. Use msleep to replace the busy
> waiting cpu_relax() and remove the warning message.
> 
> Signed-off-by: Bryan Wu <bryan.wu at canonical.com>
> ---
>  drivers/net/fec.c |   45 +++++++++++++++++++++------------------------
>  1 files changed, 21 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/net/fec.c b/drivers/net/fec.c
> index 53240d3..2280373 100644
> --- a/drivers/net/fec.c
> +++ b/drivers/net/fec.c
> @@ -216,7 +216,7 @@ static void fec_stop(struct net_device *dev);
>  #define FEC_MMFR_TA		(2 << 16)
>  #define FEC_MMFR_DATA(v)	(v & 0xffff)
>  
> -#define FEC_MII_TIMEOUT		10000
> +#define FEC_MII_TIMEOUT		10
>  
>  /* Transmitter timeout */
>  #define TX_TIMEOUT (2 * HZ)
> @@ -624,13 +624,29 @@ spin_unlock:
>  /*
>   * NOTE: a MII transaction is during around 25 us, so polling it...
>   */
> -static int fec_enet_mdio_read(struct mii_bus *bus, int mii_id, int regnum)
> +static int fec_enet_mdio_poll(struct fec_enet_private *fep)
>  {
> -	struct fec_enet_private *fep = bus->priv;
>  	int timeout = FEC_MII_TIMEOUT;
>  
>  	fep->mii_timeout = 0;
>  
> +	/* wait for end of transfer */
> +	while (!(readl(fep->hwp + FEC_IEVENT) & FEC_ENET_MII)) {
> +		msleep(1);
> +		if (timeout-- < 0) {
> +			fep->mii_timeout = 1;
> +			break;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +static int fec_enet_mdio_read(struct mii_bus *bus, int mii_id, int regnum)
> +{
> +	struct fec_enet_private *fep = bus->priv;
> +
> +
>  	/* clear MII end of transfer bit*/
>  	writel(FEC_ENET_MII, fep->hwp + FEC_IEVENT);
>  
> @@ -639,15 +655,7 @@ static int fec_enet_mdio_read(struct mii_bus *bus, int mii_id, int regnum)
>  		FEC_MMFR_PA(mii_id) | FEC_MMFR_RA(regnum) |
>  		FEC_MMFR_TA, fep->hwp + FEC_MII_DATA);
>  
> -	/* wait for end of transfer */
> -	while (!(readl(fep->hwp + FEC_IEVENT) & FEC_ENET_MII)) {
> -		cpu_relax();
> -		if (timeout-- < 0) {
> -			fep->mii_timeout = 1;
> -			printk(KERN_ERR "FEC: MDIO read timeout\n");
> -			return -ETIMEDOUT;
> -		}
> -	}
> +	fec_enet_mdio_poll(fep);

You have pulled out this timeout loop, but in the replacement there is
not indication that it has timed-out.  In the old code we would have
returned -ETIMEDOUT and not touched MII_DATA (below).  In the new we
will timeout, mark mii_timeout but not return an indication of that, not
would we note it here, and so we would drop through and touch MII_DATA.
Is this an intentional change of semantics?

>  
>  	/* return value */
>  	return FEC_MMFR_DATA(readl(fep->hwp + FEC_MII_DATA));
> @@ -657,9 +665,6 @@ static int fec_enet_mdio_write(struct mii_bus *bus, int mii_id, int regnum,
>  			   u16 value)
>  {
>  	struct fec_enet_private *fep = bus->priv;
> -	int timeout = FEC_MII_TIMEOUT;
> -
> -	fep->mii_timeout = 0;
>  
>  	/* clear MII end of transfer bit*/
>  	writel(FEC_ENET_MII, fep->hwp + FEC_IEVENT);
> @@ -670,15 +675,7 @@ static int fec_enet_mdio_write(struct mii_bus *bus, int mii_id, int regnum,
>  		FEC_MMFR_TA | FEC_MMFR_DATA(value),
>  		fep->hwp + FEC_MII_DATA);
>  
> -	/* wait for end of transfer */
> -	while (!(readl(fep->hwp + FEC_IEVENT) & FEC_ENET_MII)) {
> -		cpu_relax();
> -		if (timeout-- < 0) {
> -			fep->mii_timeout = 1;
> -			printk(KERN_ERR "FEC: MDIO write timeout\n");
> -			return -ETIMEDOUT;
> -		}
> -	}
> +	fec_enet_mdio_poll(fep);
>  
>  	return 0;
>  }

-apw