linux-kernel - Re: [PATCH 09/15] net: phy: delay PHY driver probe until PHY registration

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Message-ID: <20200624094302.GA5472@sirena.org.uk>
Date:   Wed, 24 Jun 2020 10:43:02 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, Bartosz Golaszewski <brgl@...ev.pl>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Yisen Zhuang <yisen.zhuang@...wei.com>,
        Salil Mehta <salil.mehta@...wei.com>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Iyappan Subramanian <iyappan@...amperecomputing.com>,
        Keyur Chudgar <keyur@...amperecomputing.com>,
        Quan Nguyen <quan@...amperecomputing.com>,
        Frank Rowand <frowand.list@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Liam Girdwood <lgirdwood@...il.com>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Fabien Parent <fparent@...libre.com>,
        Stephane Le Provost <stephane.leprovost@...iatek.com>,
        Pedro Tsai <pedro.tsai@...iatek.com>,
        Andrew Perepech <andrew.perepech@...iatek.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 09/15] net: phy: delay PHY driver probe until PHY
 registration

On Tue, Jun 23, 2020 at 12:49:15PM -0700, Florian Fainelli wrote:
> On 6/22/20 6:51 AM, Mark Brown wrote:

> > If the bus includes power management for the devices on the bus the
> > controller is generally responsible for that rather than the devices,
> > the devices access this via facilities provided by the bus if needed.
> > If the device is enumerated by firmware prior to being physically
> > enumerable then the bus will generally instantiate the device model
> > device and then arrange to wait for the physical device to appear and
> > get joined up with the device model device, typically in such situations
> > the physical device might appear and disappear dynamically at runtime
> > based on what the driver is doing anyway.

> In premise there is nothing that prevents the MDIO bus from taking care
> of the regulators, resets, prior to probing the PHY driver, what is
> complicated here is that we do need to issue a read of the actual PHY to
> know its 32-bit unique identifier and match it with an appropriate
> driver. The way that we have worked around this with if you do not wish
> such a hardware access to be made, is to provide an Ethernet PHY node
> compatible string that encodes that 32-bit OUI directly. In premise the
> same challenges exist with PCI devices/endpoints as well as USB, would
> they have reset or regulator typically attached to them.

That all sounds very normal and is covered by both cases I describe?

> > We could use a pre-probe stage in the device model for hotpluggable
> > buses in embedded contexts where you might need to bring things out of
> > reset or power them up before they'll appear on the bus for enumeration
> > but buses have mostly handled that at their level.

> That sounds like a better solution, are there any subsystems currently
> implementing that, or would this be a generic Linux device driver model
> addition that needs to be done?

Like I say I'm suggesting doing something at the device model level.

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