Re: Spurious timeouts in mvmdio

[Leigh Brown]

On 2013-12-03 23:17, Sebastian Hesselbarth wrote:
> On 12/04/2013 12:20 AM, Leigh Brown wrote:
> > On 2013-12-03 22:45, Sebastian Hesselbarth wrote:
> > > On 12/03/2013 09:57 PM, Leigh Brown wrote:
> > [...]
> > > > Nicolas' patch should fix the issue, but I prefer the following as 
> > > > it is
> > > > more
> > > > correct, as it only adjusts the timeout when calling
> > > > wait_event_timeout().  As
> > > > I said above,I believe the polling code is correct.
> > > >
> > > > diff --git a/drivers/net/ethernet/marvell/mvmdio.c
> > > > b/drivers/net/ethernet/marvell/mvmdio.c
> > > > index 7354960..b187c08 100644
> > > > --- a/drivers/net/ethernet/marvell/mvmdio.c
> > > > +++ b/drivers/net/ethernet/marvell/mvmdio.c
> > > > @@ -92,6 +92,14 @@ static int orion_mdio_wait_ready(struct mii_bus 
> > > > *bus)
> > > >               if (time_is_before_jiffies(end))
> > > >                   ++timedout;
> > > >               } else {
> > > > +            /*
> > > > +             * wait_event_timeout does not guarantee a delay of at
> > > > +             * least one whole jiffie, so timeout must be no less
> > > > +             * than two.
> > > > +             */
> > > > +            if (timeout < 2)
> > > > +                timeout = 2;
> > >
> > > If you always want to wait at least two jiffies, why not just 
> > > increase
> > > TIMEOUT makro to 20ms instead of messing here with it again?
> > > As said on IRC log above, originally timeout was 100ms.
> >
> > You could do that, but would you not feel bad leaving a latent bug in
> > the code?
> > I know it's unlikely that someone would set HZ to 50, but if they did,
> > the same
> > bug would appear again.
>
> If you want to ensure timeout > 2, why not then just use:
>
> - 	unsigned long timeout = usecs_to_jiffies(MVMDIO_SMI_TIMEOUT);
> + 	unsigned long timeout = 1 + usecs_to_jiffies(MVMDIO_SMI_TIMEOUT);

This will make it correct when using interrupts but it will make the 
loop wait one
jiffie longer than it should when polling.

I think I might be being a little to anal about this, but I guess what 
you could do
is make the above change, then replace the call to 
time_is_before_jiffies() with
time_is_before_eq_jiffies() so that the behaviour when polling and when 
using
interrupts is the same.

diff --git a/drivers/net/ethernet/marvell/mvmdio.c 
b/drivers/net/ethernet/marvell/mvmdio.c
index 7354960..48b8ded 100644
--- a/drivers/net/ethernet/marvell/mvmdio.c
+++ b/drivers/net/ethernet/marvell/mvmdio.c
@@ -75,7 +75,7 @@ static int orion_mdio_smi_is_done(struct 
orion_mdio_dev *dev)
 static int orion_mdio_wait_ready(struct mii_bus *bus)
 {
 	struct orion_mdio_dev *dev = bus->priv;
-	unsigned long timeout = usecs_to_jiffies(MVMDIO_SMI_TIMEOUT);
+	unsigned long timeout = 1 + usecs_to_jiffies(MVMDIO_SMI_TIMEOUT);
 	unsigned long end = jiffies + timeout;
 	int timedout = 0;

@@ -89,7 +89,7 @@ static int orion_mdio_wait_ready(struct mii_bus *bus)
 			usleep_range(MVMDIO_SMI_POLL_INTERVAL_MIN,
 				     MVMDIO_SMI_POLL_INTERVAL_MAX);

-			if (time_is_before_jiffies(end))
+			if (time_is_before_eq_jiffies(end))
 				++timedout;
 	        } else {
 			wait_event_timeout(dev->smi_busy_wait,

Regards,

Leigh.
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