netdev - Re: [PATCH net-next 0/3] net: phy: Support enabling clocks prior to bus probe

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Message-ID: <20200904142347.GP3112546@lunn.ch>
Date:   Fri, 4 Sep 2020 16:23:47 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Adam Rudziński <adam.rudzinski@....net.pl>
Cc:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org,
        m.felsch@...gutronix.de, hkallweit1@...il.com,
        richard.leitner@...data.com, zhengdejin5@...il.com,
        devicetree@...r.kernel.org, kernel@...gutronix.de, kuba@...nel.org,
        robh+dt@...nel.org
Subject: Re: [PATCH net-next 0/3] net: phy: Support enabling clocks prior to
 bus probe

On Fri, Sep 04, 2020 at 04:00:55PM +0200, Adam Rudziński wrote:
> W dniu 2020-09-04 o 15:45, Andrew Lunn pisze:
> > > Just a bunch of questions.
> > > 
> > > Actually, why is it necessary to have a full MDIO bus scan already during
> > > probing peripherals?
> > That is the Linux bus model. It does not matter what sort of bus it
> > is, PCI, USB, MDIO, etc. When the bus driver is loaded, the bus is
> > enumerated and drivers probe for each device found on the bus.
> 
> OK. But is it always expected to find all the devices on the bus in the
> first run?

Yes. Cold plug expects to find all the device while scanning the bus.

> Does the bus model ever allow to just add any more devices? Kind of,
> "hotplug". :)

Hotplug is triggered by hardware saying a new device has been
added/removed after cold plug.

This is not a hotplug case. The hardware has not suddenly appeared, it
has always been there.

   Andrew