Re: [PATCH v4 09/10] net: eth: altera: add msgdma prefetcher

Jakub Kicinski
2020-07-14T16:29:07Z

On Tue, 14 Jul 2020 15:58:53 +0000 Westergreen, Dalon wrote:
> On Tue, 2020-07-14 at 08:55 -0700, Jakub Kicinski wrote:
> > On Tue, 14 Jul 2020 14:35:16 +0000 Ooi, Joyce wrote:
> > > > I'm no device tree expert but these look like config options rather than
> > > > HW
> > > > description. They also don't appear to be documented in the next patch.
> > >
> > > The poll_freq are part of the msgdma prefetcher IP, whereby it
> > > specifies the frequency of descriptor polling operation. I can add
> > > the poll_freq description in the next patch.
> >
> > Is the value decided at the time of synthesis or can the driver choose
> > the value it wants?
>
> It is not controlled at synthesis, this parameter should likely not be a
> devicetree parameter, perhaps just make it a module parameter with a default
> value.

Let's see if I understand the feature - instead of using a doorbell the
HW periodically checks the contents of the next-to-use descriptor to
see if it contains a valid tx frame or rx buffer?

I've seen vendors abuse fields of ethtool --coalesce to configure
similar settings. tx-usecs-irq and rx-usecs-irq, I think. Since this
part of ethtool API has been ported to netlink, could we perhaps add
a new field to ethtool --coalesce?