netdev - Re: [PATCH 2/2] net: xilinx_emaclite: recheck condition after timeout in mdio

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Message-ID: <20181030121030.GD27873@lunn.ch>
Date:   Tue, 30 Oct 2018 13:10:30 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Kurt Kanzenbach <kurt@...utronix.de>
Cc:     Anirudha Sarangi <anirudh@...inx.com>,
        John Linn <John.Linn@...inx.com>,
        "David S. Miller" <davem@...emloft.net>,
        Michal Simek <michal.simek@...inx.com>,
        Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>,
        YueHaibing <yuehaibing@...wei.com>, netdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] net: xilinx_emaclite: recheck condition after
 timeout in mdio_wait()

On Tue, Oct 30, 2018 at 10:31:39AM +0100, Kurt Kanzenbach wrote:
> The function could report a false positive if it gets preempted between reading
> the XEL_MDIOCTRL_OFFSET register and checking for the timeout.  In such a case,
> the condition has to be rechecked to avoid false positives.
> 
> Therefore, check for expected condition even after the timeout occurred.
> 
> Signed-off-by: Kurt Kanzenbach <kurt@...utronix.de>
> ---
>  drivers/net/ethernet/xilinx/xilinx_emaclite.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/xilinx/xilinx_emaclite.c b/drivers/net/ethernet/xilinx/xilinx_emaclite.c
> index 639e3e99af46..957d03085bd0 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_emaclite.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_emaclite.c
> @@ -714,19 +714,29 @@ static irqreturn_t xemaclite_interrupt(int irq, void *dev_id)
>  static int xemaclite_mdio_wait(struct net_local *lp)
>  {
>  	unsigned long end = jiffies + 2;
> +	u32 val;
>  
>  	/* wait for the MDIO interface to not be busy or timeout
>  	 * after some time.
>  	 */
> -	while (xemaclite_readl(lp->base_addr + XEL_MDIOCTRL_OFFSET) &
> -			XEL_MDIOCTRL_MDIOSTS_MASK) {
> +	while (1) {
> +		val = xemaclite_readl(lp->base_addr + XEL_MDIOCTRL_OFFSET);

Hi Kurt

It looks like readx_poll_timeout() should work here.

   Andrew