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

Johannes Berg
2021-09-01T17:08:20Z

On Wed, 2021-09-01 at 18:51 +0200, Heiner Kallweit wrote:
> On 01.09.2021 17:51, Pali Rohár wrote:
> > On Wednesday 01 September 2021 16:01:54 Jonas Dreßler wrote:
> > > On 8/30/21 2:49 PM, Andy Shevchenko wrote:
> > > > On Mon, Aug 30, 2021 at 3:38 PM Jonas Dreßler <verdre@v0yd.nl> 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).
> > > > >
>
> This sounds somehow like the typical case where you write DMA descriptors
> and then ring the doorbell. This normally requires a dma_wmb().
> Maybe something like that is missing here?

But it looks like this "TX ring write pointer" is actually the register?

However, I would agree that doing it in mwifiex_write_reg() is possibly
too big a hammer - could be done only for reg->tx_wrptr, not all the
registers?

Actually, can two writes actually cross on PCI?

johannes