Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs

Benjamin Herrenschmidt
2020-09-14T21:42:55Z

On Mon, 2020-09-14 at 11:17 -0300, Jason Gunthorpe wrote:
> On Fri, Sep 11, 2020 at 09:42:25PM +0000, Clint Sbisa wrote:
>
> > There's no DMA involved with this BAR-- the driver writes a portion
> > of the
> > packet contents in addition to the descriptors, which generally
> > increases the
> > number of TLPs if write-combine isn't used. Furthermore, this BAR
> > is only used
> > for writes and never for reads.
>
> You use DPDK without DMA? How does receive work?
>
> > As Jason noted in the other reply to this email, the Linux ENA
> > driver makes use
> > of WC by using devm_ioremap_wc().
>
> As Ben noted we don't have kernel accessors to make this portable or
> safe :(

Well.. to be frank it does work "well enough" for simple cases like
frame buffers :-)

Cheers
Ben.