Subject: Re: [PATCH v2 net-next] drivers: net: davinci_mdio: prevent spurious timeout

From: Andrew Lunn <[email-masked]>
Date: Wed, 9 May 2018 15:30:14 +0200

On Wed, May 09, 2018 at 04:30:24PM +0530, Sekhar Nori wrote:
> A well timed kernel preemption in the time_after() loop
> in wait_for_idle() can result in a spurious timeout
> error to be returned.
> 
> Fix it by using readl_poll_timeout() which takes care of
> this issue.
> 
> Signed-off-by: Sekhar Nori <[email-masked]>
> ---
> v2: use readl_poll_timeout() per suggestion from Andrew.
> 
> The issue has not been personally observed by me, but has
> been reported by users. Sending for next-next given the
> non-critical nature. There is seems to be no easy way to
> reproduce this.
> 
>  drivers/net/ethernet/ti/davinci_mdio.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/ti/davinci_mdio.c b/drivers/net/ethernet/ti/davinci_mdio.c
> index 3c33f4504d8e..d073432a5dbe 100644
> --- a/drivers/net/ethernet/ti/davinci_mdio.c
> +++ b/drivers/net/ethernet/ti/davinci_mdio.c
> @@ -34,6 +34,7 @@
>  #include <linux/clk.h>
>  #include <linux/err.h>
>  #include <linux/io.h>
> +#include <linux/iopoll.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/davinci_emac.h>
>  #include <linux/of.h>
> @@ -227,14 +228,16 @@ static inline int wait_for_user_access(struct davinci_mdio_data *data)
>  static inline int wait_for_idle(struct davinci_mdio_data *data)
>  {
>  	struct davinci_mdio_regs __iomem *regs = data->regs;
> -	unsigned long timeout = jiffies + msecs_to_jiffies(MDIO_TIMEOUT);
> +	u32 val, ret;
>  
> -	while (time_after(timeout, jiffies)) {
> -		if (__raw_readl(&regs->control) & CONTROL_IDLE)
> -			return 0;
> +	ret = readl_poll_timeout(&regs->control, val, val & CONTROL_IDLE,
> +				 0, MDIO_TIMEOUT * 1000);
> +	if (ret) {
> +		dev_err(data->dev, "timed out waiting for idle\n");
> +		return ret;
>  	}
> -	dev_err(data->dev, "timed out waiting for idle\n");
> -	return -ETIMEDOUT;
> +
> +	return 0;
>  }

Hi Sekhar

You could simplify this to:

> +	if (ret)
> +		dev_err(data->dev, "timed out waiting for idle\n");
> +	return ret;

Reviewed-by: Andrew Lunn <[email-masked]>

    Andrew