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

Jason Gunthorpe
2020-09-14T14:18:49Z

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 :(

Jason