linux-kernel - Re: [RFC PATCH 1/5] net: macb: Check MDIO state before read/write and use timeouts

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Message-ID: <81b5b276-e59c-79d8-1616-79ff0e9c5f17@microchip.com>
Date:   Thu, 3 May 2018 13:08:43 +0300
From:   Claudiu Beznea <Claudiu.Beznea@...rochip.com>
To:     <harinikatakamlinux@...il.com>, <nicolas.ferre@...el.com>,
        <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <harinik@...inx.com>, <michals@...inx.com>, <appanad@...inx.com>,
        Shubhrajyoti Datta <shubhrajyoti.datta@...inx.com>
Subject: Re: [RFC PATCH 1/5] net: macb: Check MDIO state before read/write and
 use timeouts



On 22.03.2018 15:51, harinikatakamlinux@...il.com wrote:
> From: Harini Katakam <harinik@...inx.com>
> 
> Replace the while loop in MDIO read/write functions with a timeout.
> In addition, add a check for MDIO bus busy before initiating a new
> operation as well to make sure there is no ongoing MDIO operation.
> 
> Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@...inx.com>
> Signed-off-by: Harini Katakam <harinik@...inx.com>
> ---
>  drivers/net/ethernet/cadence/macb_main.c | 54 ++++++++++++++++++++++++++++++--
>  1 file changed, 52 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index d09bd43..f4030c1 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -321,6 +321,21 @@ static int macb_mdio_read(struct mii_bus *bus, int mii_id, int regnum)
>  {
>  	struct macb *bp = bus->priv;
>  	int value;
> +	ulong timeout;
> +
> +	timeout = jiffies + msecs_to_jiffies(1000);
> +	/* wait for end of transfer */
> +	do {
> +		if (MACB_BFEXT(IDLE, macb_readl(bp, NSR)))
> +			break;
> +
> +		cpu_relax();
> +	} while (!time_after_eq(jiffies, timeout));
> +
> +	if (time_after_eq(jiffies, timeout)) {
> +		netdev_err(bp->dev, "wait for end of transfer timed out\n");
> +		return -ETIMEDOUT;
> +	}

Wouldn't be cleaner to keep it in this way:

	while (!MACB_BFEXT(IDLE, macb_readl(bp, NSR))) {
		if (time_after_eq(jiffies, timeout) {
			netdev_err(bp->dev, "wait for end of transfer timed out\n");
			return -ETIMEDOUT;
		}
		cpu_relax();
	}

>  
>  	macb_writel(bp, MAN, (MACB_BF(SOF, MACB_MAN_SOF)
>  			      | MACB_BF(RW, MACB_MAN_READ)
> @@ -328,9 +343,19 @@ static int macb_mdio_read(struct mii_bus *bus, int mii_id, int regnum)
>  			      | MACB_BF(REGA, regnum)
>  			      | MACB_BF(CODE, MACB_MAN_CODE)));
>  
> +	timeout = jiffies + msecs_to_jiffies(1000);
>  	/* wait for end of transfer */
> -	while (!MACB_BFEXT(IDLE, macb_readl(bp, NSR)))
> +	do {
> +		if (MACB_BFEXT(IDLE, macb_readl(bp, NSR)))
> +			break;
> +
>  		cpu_relax();
> +	} while (!time_after_eq(jiffies, timeout));
> +
> +	if (time_after_eq(jiffies, timeout)) {
> +		netdev_err(bp->dev, "wait for end of transfer timed out\n");
> +		return -ETIMEDOUT;
> +	}
>  
>  	value = MACB_BFEXT(DATA, macb_readl(bp, MAN));
>  
> @@ -341,6 +366,21 @@ static int macb_mdio_write(struct mii_bus *bus, int mii_id, int regnum,
>  			   u16 value)
>  {
>  	struct macb *bp = bus->priv;
> +	ulong timeout;
> +
> +	timeout = jiffies + msecs_to_jiffies(1000);
> +	/* wait for end of transfer */
> +	do {
> +		if (MACB_BFEXT(IDLE, macb_readl(bp, NSR)))
> +			break;
> +
> +		cpu_relax();
> +	} while (!time_after_eq(jiffies, timeout));
> +
> +	if (time_after_eq(jiffies, timeout)) {
> +		netdev_err(bp->dev, "wait for end of transfer timed out\n");
> +		return -ETIMEDOUT;
> +	}
>  
>  	macb_writel(bp, MAN, (MACB_BF(SOF, MACB_MAN_SOF)
>  			      | MACB_BF(RW, MACB_MAN_WRITE)
> @@ -349,9 +389,19 @@ static int macb_mdio_write(struct mii_bus *bus, int mii_id, int regnum,
>  			      | MACB_BF(CODE, MACB_MAN_CODE)
>  			      | MACB_BF(DATA, value)));
>  
> +	timeout = jiffies + msecs_to_jiffies(1000);
>  	/* wait for end of transfer */
> -	while (!MACB_BFEXT(IDLE, macb_readl(bp, NSR)))
> +	do {
> +		if (MACB_BFEXT(IDLE, macb_readl(bp, NSR)))
> +			break;
> +
>  		cpu_relax();
> +	} while (!time_after_eq(jiffies, timeout));
> +
> +	if (time_after_eq(jiffies, timeout)) {
> +		netdev_err(bp->dev, "wait for end of transfer timed out\n");
> +		return -ETIMEDOUT;
> +	}
>  
>  	return 0;
>  }
>