netdev - Re: Spurious timeouts in mvmdio

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Message-ID: <529E66A4.4050000@gmail.com>
Date:	Wed, 04 Dec 2013 00:17:56 +0100
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	Leigh Brown <leigh@...inno.co.uk>
CC:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Nicolas Schichan <nschichan@...ebox.fr>,
	Jason Cooper <jason@...edaemon.net>, netdev@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Florian Fainelli <florian@...nwrt.org>,
	"David S. Miller" <davem@...emloft.net>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: Spurious timeouts in mvmdio

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);


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