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

On Tue, 2020-07-14 at 09:29 -0700, Jakub Kicinski wrote:

On Tue, 14 Jul 2020 15:58:53 +0000 Westergreen, Dalon wrote:

quoted

On Tue, 2020-07-14 at 08:55 -0700, Jakub Kicinski wrote:

quoted

On Tue, 14 Jul 2020 14:35:16 +0000 Ooi, Joyce wrote:  

quoted

quoted

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?

Yes, it checks the next-to-use descriptor to see if the descriptor is valid.

the value specifies the number of cycles to wait before checking again

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?

I don't think this is necessary, i think just having a module parameter
meets our needs.  I don't see a need for the value to change on a per
interface basis.  This was primarily used during testing / bringup.

-dalon