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

[Jonas Dreßler]

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@xxxxxxx> 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...