linux-kernel - Re: [RFC v4 net-next 2/4] net: dsa: mt7530: add interrupt support

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Date:   Tue, 13 Apr 2021 23:29:20 +0800
From:   DENG Qingfang <dqfext@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Marc Zyngier <maz@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Sean Wang <sean.wang@...iatek.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sergio Paracuellos <sergio.paracuellos@...il.com>,
        linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-staging@...ts.linux.dev, devicetree@...r.kernel.org,
        netdev@...r.kernel.org, Weijie Gao <weijie.gao@...iatek.com>,
        Chuanhong Guo <gch981213@...il.com>,
        René van Dorst <opensource@...rst.com>,
        Frank Wunderlich <frank-w@...lic-files.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Ungerer <gerg@...nel.org>
Subject: Re: [RFC v4 net-next 2/4] net: dsa: mt7530: add interrupt support

On Tue, Apr 13, 2021 at 02:52:59PM +0200, Andrew Lunn wrote:
> > I guess this is depends whether the most usual case is to have all
> > these interrupts being actively in use or not. Most interrupts only
> > use a limited portion of their interrupt space at any given time.
> > Allocating all interrupts and creating mappings upfront is a waste of
> > memory.
> > 
> > If the use case here is that all these interrupts will be wired and
> > used in most cases, then upfront allocation is probably not a problem.
> 
> Hi Marc
> 
> The interrupts are generally used. Since this is an Ethernet switch,
> generally the port is administratively up, even if there is no cable
> plugged in. Once/if a cable is plugged in and there is a link peer,
> the PHY will interrupt to indicate this.
> 
> The only real case i can think of when the interrupts are not used is
> when the switch has more ports than connected to the front panel. This
> can happen in industrial settings, but not SOHO. Those ports which
> don't go anywhere are never configured up and so the interrupt is
> never used.

Hi Andrew

This is what the extra check (BIT(p) & ds->phys_mii_mask) avoids.

Currently the mv88e6xxx driver does not have this check, and creates
15 PHY IRQ mappings on my 88E6176 unconditionally, leaving a gap in
/proc/interrupts:

...
 57:          0          0  mv88e6xxx-g1   3 Edge      mv88e6xxx-f1072004.mdio-mii:00-g1-atu-prob
 59:          0          0  mv88e6xxx-g1   5 Edge      mv88e6xxx-f1072004.mdio-mii:00-g1-vtu-prob
 61:          8          5  mv88e6xxx-g1   7 Edge      mv88e6xxx-f1072004.mdio-mii:00-g2
 63:          8          4  mv88e6xxx-g2   0 Edge      mv88e6xxx-1:00
 64:          0          0  mv88e6xxx-g2   1 Edge      mv88e6xxx-1:01
 65:          0          0  mv88e6xxx-g2   2 Edge      mv88e6xxx-1:02
 66:          0          0  mv88e6xxx-g2   3 Edge      mv88e6xxx-1:03
 67:          0          2  mv88e6xxx-g2   4 Edge      mv88e6xxx-1:04
// IRQ 68~77 are created but not used
 78:          0          0  mv88e6xxx-g2  15 Edge      mv88e6xxx-f1072004.mdio-mii:00-watchdog
...

You may as well add irq_set_nested_thread(irq, true) to irq_domain_map
so all IRQs share a single thread.

> 
>       Andrew