linux-kernel - RE: [PATCH 2/2] net: xilinx_emaclite: recheck condition after timeout in mdio

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Message-ID: <SN4PR0201MB36306924359BB3A8BD5F19D7C7CC0@SN4PR0201MB3630.namprd02.prod.outlook.com>
Date:   Tue, 30 Oct 2018 12:58:33 +0000
From:   Radhey Shyam Pandey <radheys@...inx.com>
To:     Andrew Lunn <andrew@...n.ch>, Kurt Kanzenbach <kurt@...utronix.de>
CC:     Anirudha Sarangi <anirudh@...inx.com>,
        John Linn <linnj@...inx.com>,
        "David S. Miller" <davem@...emloft.net>,
        Michal Simek <michals@...inx.com>,
        YueHaibing <yuehaibing@...wei.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/2] net: xilinx_emaclite: recheck condition after timeout
 in mdio_wait()

<snip>
> 
> 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.

Yes, valid point. readx_poll_timeout API repoll addr after timeout.
Reusing it would simplify the flow.

> 
>    Andrew