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

[Jonas Dreßler]

On 8/30/21 2:49 PM, Andy Shevchenko wrote:
> On Mon, Aug 30, 2021 at 3:38 PM Jonas Dreßler <verdre@xxxxxxx> wrote:
>>
>> On the 88W8897 card it's very important the TX ring write pointer is
>> updated correctly to its new value before setting the TX ready
>> interrupt, otherwise the firmware appears to crash (probably because
>> it's trying to DMA-read from the wrong place).
>>
>> Since PCI uses "posted writes" when writing to a register, it's not
>> guaranteed that a write will happen immediately. That means the pointer
>> might be outdated when setting the TX ready interrupt, leading to
>> firmware crashes especially when ASPM L1 and L1 substates are enabled
>> (because of the higher link latency, the write will probably take
>> longer).
>>
>> So fix those firmware crashes by always forcing non-posted writes. We do
>> that by simply reading back the register after writing it, just as a lot
>> of other drivers do.
>>
>> There are two reproducers that are fixed with this patch:
>>
>> 1) During rx/tx traffic and with ASPM L1 substates enabled (the enabled
>> substates are platform dependent), the firmware crashes and eventually a
>> command timeout appears in the logs. That crash is fixed by using a
>> non-posted write in mwifiex_pcie_send_data().
>>
>> 2) When sending lots of commands to the card, waking it up from sleep in
>> very quick intervals, the firmware eventually crashes. That crash
>> appears to be fixed by some other non-posted write included here.
>
> Thanks for all this work!
>
> Nevertheless, do we have any commits that may be a good candidate to
> be in the Fixes tag here?
>

I don't think there's any commit we could point to, given that the bug 
is probably somewhere in the firmware code.

>> Signed-off-by: Jonas Dreßler <verdre@xxxxxxx>
>> ---
>>   drivers/net/wireless/marvell/mwifiex/pcie.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/net/wireless/marvell/mwifiex/pcie.c 
b/drivers/net/wireless/marvell/mwifiex/pcie.c
>> index c6ccce426b49..bfd6e135ed99 100644
>> --- a/drivers/net/wireless/marvell/mwifiex/pcie.c
>> +++ b/drivers/net/wireless/marvell/mwifiex/pcie.c
>> @@ -237,6 +237,12 @@ static int mwifiex_write_reg(struct 
mwifiex_adapter *adapter, int reg, u32 data)
>>
>>          iowrite32(data, card->pci_mmap1 + reg);
>>
>> +       /* Do a read-back, which makes the write non-posted, 
ensuring the
>> +        * completion before returning.
>
>> +        * The firmware of the 88W8897 card is buggy and this avoids 
crashes.
>
> Any firmware version reference? Would be nice to have just for the
> sake of record.
>

Pretty sure the crash is present in every firmware that has been 
released, I've tried most of them. FTR, the current firmware version is 
15.68.19.p21.

>> +        */
>> +       ioread32(card->pci_mmap1 + reg);
>> +
>>          return 0;
>>   }
>
>