Re: [PATCH 1/2] mwifiex: Use non-posted PCI register writes

Jonas Dreßler
2021-09-30T16:14:14Z

On 9/30/21 5:42 PM, Pali Rohár wrote:
> On Thursday 30 September 2021 17:38:43 Jonas Dreßler wrote:
>> On 9/23/21 10:22 PM, Pali Rohár wrote:
>>> On Thursday 23 September 2021 22:41:30 Andy Shevchenko wrote:
>>>> On Thu, Sep 23, 2021 at 6:28 PM Jonas Dreßler <verdre@v0yd.nl> wrote:
>>>>> On 9/22/21 2:50 PM, Jonas Dreßler wrote:
>>>>
>>>> ...
>>>>
>>>>> - Just calling mwifiex_write_reg() once and then blocking until the card
>>>>> wakes up using my delay-loop doesn't fix the issue, it's actually
>>>>> writing multiple times that fixes the issue
>>>>>
>>>>> These observations sound a lot like writes (and even reads) are actually
>>>>> being dropped, don't they?
>>>>
>>>> It sounds like you're writing into a not ready (fully powered on) device.
>>>
>>> This reminds me a discussion with Bjorn about CRS response returned
>>> after firmware crash / reset when device is not ready yet:
>>> https://lore.kernel.org/linux-pci/20210922164803.GA203171@bhelgaas/
>>>
>>> Could not be this similar issue? You could check it via reading
>>> PCI_VENDOR_ID register from config space. And if it is not valid value
>>> then card is not really ready yet.
>>>
>>>> To check this, try to put a busy loop for reading and check the value
>>>> till it gets 0.
>>>>
>>>> Something like
>>>>
>>>> unsigned int count = 1000;
>>>>
>>>> do {
>>>> if (mwifiex_read_reg(...) == 0)
>>>> break;
>>>> } while (--count);
>>>>
>>>>
>>>> --
>>>> With Best Regards,
>>>> Andy Shevchenko
>>
>> I've tried both reading PCI_VENDOR_ID and the firmware status using a busy
>> loop now, but sadly none of them worked. It looks like the card always
>> replies with the correct values even though it sometimes won't wake up after
>> that.
>>
>> I do have one new observation though, although I've no clue what could be
>> happening here: When reading PCI_VENDOR_ID 1000 times to wakeup we can
>> "predict" the wakeup failure because exactly one (usually around the 20th)
>> of those 1000 reads will fail.
>
> What does "fail" means here?

ioread32() returns all ones, that's interpreted as failure by
mwifiex_read_reg().

>
>> Maybe the firmware actually tries to wake up,
>> encounters an error somewhere in its wakeup routines and then goes down a
>> special failure code path. That code path keeps the cards CPU so busy that
>> at some point a PCI_VENDOR_ID request times out?
>>
>> Or well, maybe the card actually wakes up fine, but we don't receive the
>> interrupt on our end, so many possibilities...