From: Vladimir Oltean <olteanv@gmail.com>
To: "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc: "Vladimir Oltean" <vladimir.oltean@nxp.com>,
netdev@vger.kernel.org,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
"Andrew Lunn" <andrew@lunn.ch>,
"Heiner Kallweit" <hkallweit1@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
"Jakub Kicinski" <kuba@kernel.org>,
"Vivien Didelot" <vivien.didelot@gmail.com>,
"Florian Fainelli" <f.fainelli@gmail.com>,
linux-kernel@vger.kernel.org,
"Linus Walleij" <linus.walleij@linaro.org>,
"Alvin Šipraga" <alsi@bang-olufsen.dk>,
"ACPI Devel Maling List" <linux-acpi@vger.kernel.org>,
kernel-team <kernel-team@android.com>,
"Len Brown" <lenb@kernel.org>
Subject: Re: [RFC PATCH net-next 0/3] Make the PHY library stop being so greedy when binding the generic PHY driver
Date: Thu, 2 Sep 2021 15:59:23 +0300 [thread overview]
Message-ID: <20210902125923.v7fq26iiqydtgq7g@skbuf> (raw)
In-Reply-To: <20210902123532.ruvuecxoig67yv5v@skbuf>
On Thu, Sep 02, 2021 at 03:35:32PM +0300, Vladimir Oltean wrote:
> On Thu, Sep 02, 2021 at 01:19:27PM +0100, Russell King (Oracle) wrote:
> > On Thu, Sep 02, 2021 at 01:50:50AM +0300, Vladimir Oltean wrote:
> > > The central point of that discussion is that DSA seems "broken" for
> > > expecting the PHY driver to probe immediately on PHYs belonging to the
> > > internal MDIO buses of switches. A few suggestions were made about what
> > > to do, but some were not satisfactory and some did not solve the problem.
> >
> > I think you need to describe the mechanism here. Why wouldn't a PHY
> > belonging to an internal MDIO bus of a switch not probe immediately?
> > What resources may not be available?
>
> As you point out below, the interrupt-controller is what is not available.
> There is a mechanism called fw_devlink which infers links from one OF
> node to another based on phandles. When you have an interrupt-parent,
> that OF node becomes a supplier to you. Those OF node links are then
> transferred to device links once the devices having those OF nodes are
> created.
>
> > If we have a DSA driver that tries to probe the PHYs before e.g. the
> > interrupt controller inside the DSA switch has been configured, aren't
> > we just making completely unnecessary problems for ourselves?
>
> This is not what happens, if that were the case, of course I would fix
> _that_ and not in this way.
>
> > Wouldn't it be saner to ensure that the interrupt controller has been
> > setup and become available prior to attempting to setup anything that
> > relies upon that interrupt controller?
>
> The interrupt controller _has_ been set up. The trouble is that the
> interrupt controller has the same OF node as the switch itself, and the
> same OF node. Therefore, fw_devlink waits for the _entire_ switch to
...and the same struct device, not "OF node" repeated twice, silly me.
> finish probing, it doesn't have insight into the fact that the
> dependency is just on the interrupt controller.
>
> > From what I see of Marvell switches, the internal PHYs only ever rely
> > on internal resources of the switch they are embedded in.
> >
> > External PHYs to the switch are a different matter - these can rely on
> > external clocks, and in that scenario, it would make sense for a
> > deferred probe to cause the entire switch to defer, since we don't
> > have all the resources for the switch to be functional (and, because we
> > want the PHYs to be present at switch probe time, not when we try to
> > bring up the interface, I don't see there's much other choice.)
> >
> > Trying to move that to interface-up time /will/ break userspace - for
> > example, Debian's interfaces(8) bridge support will become unreliable,
> > and probably a whole host of other userspace. It will cause regressions
> > and instability to userspace. So that's a big no.
>
> Why a big no? I expect there to be 2 call paths of phy_attach_direct:
> - At probe time. Both the MAC driver and the PHY driver are probing.
> This is what has this patch addresses. There is no issue to return
> -EPROBE_DEFER at that time, since drivers connect to the PHY before
> they register their netdev. So if connecting defers, there is no
> netdev to unregister, and user space knows nothing of this.
> - At .ndo_open time. This is where it maybe gets interesting, but not to
> user space. If you open a netdev and it connects to the PHY then, I
> wouldn't expect the PHY to be undergoing a probing process, all of
> that should have been settled by then, should it not? Where it might
> get interesting is with NFS root, and I admit I haven't tested that.
next prev parent reply other threads:[~2021-09-02 12:59 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-01 22:50 [RFC PATCH net-next 0/3] Make the PHY library stop being so greedy when binding the generic PHY driver Vladimir Oltean
2021-09-01 22:50 ` [RFC PATCH net-next 1/3] net: phy: don't bind genphy in phy_attach_direct if the specific driver defers probe Vladimir Oltean
2021-09-02 5:43 ` Greg Kroah-Hartman
2021-09-02 10:11 ` Vladimir Oltean
2021-09-02 10:37 ` Greg Kroah-Hartman
2021-09-02 11:17 ` Vladimir Oltean
2021-09-02 14:37 ` Rafael J. Wysocki
2021-09-02 18:50 ` Russell King (Oracle)
2021-09-02 19:23 ` Vladimir Oltean
2021-09-02 19:51 ` Andrew Lunn
2021-09-02 20:33 ` Florian Fainelli
2021-09-02 21:33 ` Russell King (Oracle)
2021-09-02 21:39 ` Vladimir Oltean
2021-09-02 22:24 ` Russell King (Oracle)
2021-09-02 22:45 ` Vladimir Oltean
2021-09-02 23:02 ` Andrew Lunn
2021-09-02 23:26 ` Vladimir Oltean
2021-09-03 0:04 ` Russell King (Oracle)
2021-09-03 20:48 ` Vladimir Oltean
2021-09-03 22:06 ` Russell King (Oracle)
2021-09-04 21:59 ` Vladimir Oltean
2021-09-04 23:25 ` Russell King (Oracle)
2021-09-05 0:41 ` Vladimir Oltean
2021-09-03 9:27 ` Ioana Ciornei
2021-09-01 22:50 ` [RFC PATCH net-next 2/3] net: dsa: destroy the phylink instance on any error in dsa_slave_phy_setup Vladimir Oltean
2021-09-02 12:25 ` Russell King (Oracle)
2021-09-02 23:21 ` Florian Fainelli
2021-09-01 22:50 ` [RFC PATCH net-next 3/3] net: dsa: allow the phy_connect() call to return -EPROBE_DEFER Vladimir Oltean
2021-09-02 12:19 ` [RFC PATCH net-next 0/3] Make the PHY library stop being so greedy when binding the generic PHY driver Russell King (Oracle)
2021-09-02 12:35 ` Vladimir Oltean
2021-09-02 12:59 ` Vladimir Oltean [this message]
2021-09-02 13:26 ` Russell King (Oracle)
2021-09-02 15:23 ` Vladimir Oltean
2021-09-02 16:31 ` Russell King (Oracle)
2021-09-02 17:10 ` Vladimir Oltean
2021-09-02 17:50 ` Russell King (Oracle)
2021-09-02 19:05 ` Vladimir Oltean
2021-09-02 20:03 ` Russell King (Oracle)
2021-09-02 20:21 ` Vladimir Oltean
2021-09-02 20:29 ` Russell King (Oracle)
2021-09-03 16:22 ` Vladimir Oltean
2021-09-03 17:21 ` Andrew Lunn
2021-09-03 18:58 ` Russell King (Oracle)
2021-09-03 19:56 ` Andrew Lunn
2021-09-03 20:08 ` Russell King (Oracle)
2021-09-03 18:54 ` Russell King (Oracle)
2021-09-03 20:11 ` Vladimir Oltean
2021-09-02 20:07 ` Andrew Lunn
2021-09-02 20:32 ` Vladimir Oltean
2021-09-02 21:39 ` Russell King (Oracle)
2021-09-02 22:05 ` Vladimir Oltean
2021-09-02 23:29 ` Saravana Kannan
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