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SubjectRe: Spurious timeouts in mvmdio
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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