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Date:   Wed, 24 Jun 2020 10:43:02 +0100
From:   Mark Brown <broonie@kernel.org>
To:     Florian Fainelli <f.fainelli@gmail.com>
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Subject: Re: [PATCH 09/15] net: phy: delay PHY driver probe until PHY
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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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