netdev - Re: [RFC PATCH v2 1/5] leds: trigger: add API for HW offloading of triggers

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Date:   Mon, 8 Nov 2021 21:15:06 +0100
From:   Ansuel Smith <ansuelsmth@...il.com>
To:     Marek Behún <kabel@...nel.org>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Jonathan Corbet <corbet@....net>, Pavel Machek <pavel@....cz>,
        John Crispin <john@...ozen.org>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-leds@...r.kernel.org
Subject: Re: [RFC PATCH v2 1/5] leds: trigger: add API for HW offloading of
 triggers

On Mon, Nov 08, 2021 at 09:11:10PM +0100, Marek Behún wrote:
> On Mon, 8 Nov 2021 20:53:36 +0100
> Andrew Lunn <andrew@...n.ch> wrote:
> 
> > > I guess I will have to work on this again ASAP or we will end up with
> > > solution that I don't like.
> > > 
> > > Nonetheless, what is your opinion about offloading netdev trigger vs
> > > introducing another trigger?  
> > 
> > It is a solution that fits the general pattern, do it in software, and
> > offload it if possible.
> > 
> > However, i'm not sure the software solution actually works very well.
> > At least for switches. The two DSA drivers which implement
> > get_stats64() simply copy the cached statistics. The XRS700X updates
> > its cached values every 3000ms. The ar9331 is the same. Those are the
> > only two switch drivers which implement get_stats64 and none implement
> > get_stats. There was also was an issue that get_stats64() cannot
> > perform blocking calls. I don't remember if that was fixed, but if
> > not, get_stats64() is going to be pretty useless on switches.
> > 
> > We also need to handle drivers which don't actually implement
> > dev_get_stats(). That probably means only supporting offloads, all
> > modes which cannot be offloaded need to be rejected. This is pretty
> > much the same case of software control of the LEDs is not possible.
> > Unfortunately, dev_get_stats() does not return -EOPNOTSUPP, you need
> > to look at dev->netdev_ops->ndo_get_stats64 and
> > dev->netdev_ops->ndo_get_stats.
> > 
> > Are you working on Marvell switches? Have you implemented
> > get_stats64() for mv88e6xxx? How often do you poll the hardware for
> > the stats?
> > 
> > Given this, i think we need to bias the API so that it very likely
> > ends up offloading, if offloading is available.
> 
> I am working with Marvell PHYs and Marvell switches. I am aware of the
> problem that SW netdev does not work for switches because we don't have
> uptodate data.
> 
> It seems to me that yes, if the user wants to blink the LEDs on
> activity on switch port, the netdev trigger should only work in offload
> mode and only on LEDs that are connected to switch pins, unless we
> implement a mechanism to get statistics at lest 10 times a second
> (which could maybe be done on marvell switches by reading the registers
> via ethernet frames instead of MDIO).
> 
> Marvell switches don't seem to support rx only / tx only activity
> blinking, only rx/tx. I think this could be solved by making rx/tx
> sysfs files for netdev trigger behave so that writing to one would also
> write to another.
> 
> But since currently netdev trigger does not work for these switches, I
> think making it so that it works at least to some fashion (in HW
> supported modes) would still be better that current situation.
> 
> I will try to look into this, maybe work together with Ansuel.
> 
> Marek

I'm polishing some api with Andrew comments and will try to extend
netdev trigger while still proposing the additional trigger. Better
discuss in v3.
I think the main target here is first have a good generic solution for
offload and then actually thinking about working on the triggers/offload
part.

-- 
	Ansuel