Re: [PATCH v2] ath10k: Retry pci probe on failure.

[Ben Greear <greearb@candelatech.com>]

On 10/17/2017 01:45 AM, Kalle Valo wrote:
> Ben Greear <greearb@candelatech.com> writes:
>
>> On 10/13/2017 08:50 AM, Adrian Chadd wrote:
>>> On 13 October 2017 at 05:41, Kalle Valo <kvalo@qca.qualcomm.com> wrote:
>>>> greearb@candelatech.com writes:
>>>>
>>>>> From: Ben Greear <greearb@candelatech.com>
>>>>>
>>>>> This works around a problem we see when sometimes the wifi NIC does
>>>>> not respond the first time.  This seems to happen especially often on
>>>>> some of the 9984 NICs in mid-range platforms.
>>>>>
>>>>> Signed-off-by: Ben Greear <greearb@candelatech.com>
>>>>
>>>> [...]
>>>>
>>>>> -static int ath10k_pci_probe(struct pci_dev *pdev,
>>>>> -                         const struct pci_device_id *pci_dev)
>>>>> +static int __ath10k_pci_probe(struct pci_dev *pdev,
>>>>> +                           const struct pci_device_id *pci_dev)
>>>>>   {
>>>>>        int ret = 0;
>>>>>        struct ath10k *ar;
>>>>> @@ -3672,6 +3672,22 @@ static int ath10k_pci_probe(struct pci_dev *pdev,
>>>>>        return ret;
>>>>>   }
>>>>>
>>>>> +static int ath10k_pci_probe(struct pci_dev *pdev,
>>>>> +                         const struct pci_device_id *pci_dev)
>>>>> +{
>>>>> +     int cnt = 0;
>>>>> +     int rv;
>>>>> +     do {
>>>>> +             rv = __ath10k_pci_probe(pdev, pci_dev);
>>>>> +             if (rv == 0)
>>>>> +                     return rv;
>>>>> +             pr_err("ath10k: failed to probe PCI : %d, retry-count: %d\n", rv, cnt);
>>>>> +             mdelay(10); /* let the ath10k firmware gerbil take a small break */
>>>>> +     } while (cnt++ < 10);
>>>>> +     return rv;
>>>>> +}
>>>>
>>>> This is a sledgehammer approach and it causes reload for all error
>>>> cases, like when hardware is broken or memory allocation is failing.
>>>>
>>>> When the problem happens does it always fail at the the same place? Is
>>>> it hw reset or something else? It's better to retry the invidiual action
>>>> than to do this hack. Or is it just some more delay needed somewhere?
>>>
>>> I am seeing WMI timeouts during initial firmware load and wait on
>>> QCA9984 + BCM7444S SoC.
>>> My guess is the WMI wakeup time is not "right" enough and needs to be
>>> extended a little bit.
>>>
>>> But then, I have played a lot of whackamole with WMI timeouts during
>>> my loooong porting effort..
>>
>> The failure I saw was a failure to wake pci, and from comments, it seems that
>> the current wait is longer than what should be required, and it warns on slow
>> wakes, and I never saw that warning.  So I assume that waiting longer would not help.
>>
>> I saw it fail twice in a row to wake pci and then succeed on the third
>> try, for instance,
>> when testing my patch.
>>
>> As for a big hammer, I guess we could check for certain return codes if you think
>> that is better than just retrying all failures?
>
> ath10k_pci_probe() has a lots of stuff which should not affect your
> problem, like allocating memory, setting up timers and interrupts etc.
> It's quite ugly to redo that in every cycle. A more fine grained
> solution, like looping specific action (reset, wake whatever) is much
> more preferred.
>
> Do you have debug logs of failing cases?

I'll gather the logs next time I see this problem.

The patch I wrote likely does more than the minimal required to fix
this problem, but it does not complicate the code much, so I think that
is a benefit.  If we try to make it more specific, it will first likely
require a lot of testing effort to see if it is as effective, and second, it
will likely complicate the probe method quite a bit.

Its not like this is a performance issue...the extra loops will only be run
if the probe fails, and only on driver load.

If the driver fails to load due to issues that my hack cannot work around,
then the user has bigger problems than an extra second of time during the
boot.

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com


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