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

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Message-ID: <20200714092903.38581b74@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 14 Jul 2020 09:29:03 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Westergreen, Dalon" <dalon.westergreen@...el.com>
Cc:     "Ooi, Joyce" <joyce.ooi@...el.com>,
        "See, Chin Liang" <chin.liang.see@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Nguyen, Dinh" <dinh.nguyen@...el.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "thor.thayer@...ux.intel.com" <thor.thayer@...ux.intel.com>,
        "Tan, Ley Foon" <ley.foon.tan@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Michal Kubecek <mkubecek@...e.cz>
Subject: Re: [PATCH v4 09/10] net: eth: altera: add msgdma prefetcher

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?