Date:   Mon, 20 Mar 2023 11:27:08 +0100
From:   Jonas Gorski <jonas.gorski@...il.com>
To:     Álvaro Fernández Rojas <noltari@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        andrew@...n.ch, hkallweit1@...il.com, linux@...linux.org.uk,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] net: dsa: b53: mmap: register MDIO Mux bus controller

On Sun, 19 Mar 2023 at 10:45, Álvaro Fernández Rojas <noltari@...il.com> wrote:
>
> El vie, 17 mar 2023 a las 17:41, Florian Fainelli
> (<f.fainelli@...il.com>) escribió:
> >
> > On 3/17/23 09:23, Álvaro Fernández Rojas wrote:
> > > El vie, 17 mar 2023 a las 15:29, Vladimir Oltean (<olteanv@...il.com>) escribió:
> > >>
> > >> On Fri, Mar 17, 2023 at 03:17:12PM +0100, Álvaro Fernández Rojas wrote:
> > >>>> The proposed solution is too radical for a problem that was not properly
> > >>>> characterized yet, so this patch set has my temporary NACK.
> > >>>
> > >>> Forgive me, but why do you consider this solution too radical?
> > >>
> > >> Because it involves changing device tree bindings (stable ABI) in an
> > >> incompatible way.
> > >>
> > >>>>
> > >>>>> But maybe Florian or Jonas can give some more details about the issue...
> > >>>>
> > >>>> I think you also have the tools necessary to investigate this further.
> > >>>> We need to know what resource belonging to the switch is it that the
> > >>>> MDIO mux needs. Where is the earliest place you can add the call to
> > >>>> b53_mmap_mdiomux_init() such that your board works reliably? Note that
> > >>>> b53_switch_register() indirectly calls b53_setup(). By placing this
> > >>>> function where you have, the entirety of b53_setup() has finished
> > >>>> execution, and we don't know exactly what is it from there that is
> > >>>> needed.
> > >>>
> > >>> In the following link you will find different bootlogs related to
> > >>> different scenarios all of them with the same result: any attempt of
> > >>> calling b53_mmap_mdiomux_init() earlier than b53_switch_register()
> > >>> will either result in a kernel panic or a device hang:
> > >>> https://gist.github.com/Noltari/b0bd6d5211160ac7bf349d998d21e7f7
> > >>>
> > >>> 1. before b53_switch_register():
> > >>>
> > >>> 2. before dsa_register_switch():
> > >>>
> > >>> 3. before b53_switch_init():
> > >>
> > >> Did you read what I said?
> > >
> > > Yes, but I didn't get your point, sorry for that.
> > >
> > >>
> > >> | Note that b53_switch_register() indirectly calls b53_setup(). By placing
> > >> | this function where you have, the entirety of b53_setup() has finished
> > >> | execution, and we don't know exactly what is it from there that is
> > >> | needed.
> > >>
> > >> Can you place the b53_mmap_mdiomux_init() in various places within
> > >> b53_setup() to restrict the search further?
> > >
> > > I tried and these are the results:
> > > https://gist.github.com/Noltari/d5bdba66b8f2e392c9e4c2759661d862
> > >
> > > All of them hang when dsa_tree_setup() is called for DSA tree 1
> > > (external switch) without having completely setup DSA tree 0 (internal
> > > switch):
> > > [ 1.471345] b53-switch 10e00000.switch: found switch: BCM63xx, rev 0
> > > [ 1.481099] bcm6368-enetsw 1000d800.ethernet: IRQ tx not found
> > > [ 1.506752] bcm6368-enetsw 1000d800.ethernet: mtd mac 4c:60:de:86:52:12
> > > [ 1.594365] bcm7038-wdt 1000005c.watchdog: Registered BCM7038 Watchdog
> > > [ 1.612008] NET: Registered PF_INET6 protocol family
> > > [ 1.645617] Segment Routing with IPv6
> > > [ 1.649547] In-situ OAM (IOAM) with IPv6
> > > [ 1.653948] NET: Registered PF_PACKET protocol family
> > > [ 1.659984] 8021q: 802.1Q VLAN Support v1.8
> > > [ 1.699193] b53-switch 10e00000.switch: found switch: BCM63xx, rev 0
> > > [ 2.124257] bcm53xx 0.1:1e: found switch: BCM53125, rev 4
> > > *** Device hang ***
> > >
> > > I don't know if there's a way to defer the probe of DSA tree 1 (the
> > > external switch) until DSA tree 0 (the internal switch) is completely
> > > setup, because that would probably be the only alternative way of
> > > fixing this.
> >
> > Could you find out which part is hanging? It looks like there is a busy
> > waiting operation that we never complete?
>
> After many tests I was able to find the part that was hanging the device.
> It turns out that if the MDIO bus controller is registered soon
> enough, b53_phy_read16 will be called for the RGMII port on the
> internal switch:
> [ 4.042698] b53-switch 10e00000.switch: b53_phy_read16: ds=81fede80
> phy_read16=00000000 addr=4 reg=2
> It turns out that the device is hanging on the following line of
> b53_phy_read16():
>     b53_read16(priv, B53_PORT_MII_PAGE(addr), reg * 2, &value);
> Maybe it's not safe to access B53_PORT_MII_PAGE() on MMAP switches?

If you are following the example from 1/3, then I think I see what the
issue might be here:

You are labeling the port where the external switch is connected as
"extsw", which is neither "cpu" nor "dsa", so it is treated as a
normal/user port (which it shouldn't). If you change its label to
"dsa" (which AFAIU would be the correct one to denote a daisy chained
switch) it should not try to access port 4's MDIO registers (via the
slave mdio bus).

Can you check if that helps?

Regards
Jonas

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