netdev - netif_device_present() and Runtime PM / PCI D3

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Date:   Sun, 31 May 2020 14:07:46 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: netif_device_present() and Runtime PM / PCI D3

I just wonder about the semantics of netif_device_present().
If a device is in PCI D3 (e.g. being runtime-suspended), then it's
not accessible. So is it present or not?
The description of the function just mentions the obvious case that
the device has been removed from the system.

Related is the following regarding ethtool:
dev_ethtool() returns an error if device isn't marked as present.
If device is runtime-suspended and in PCI D3, then the driver
may still be able to provide quite some (cached) info about the
device. Same applies for settings: Even if device is sleeping,
the driver may store new settings and apply them once the device
is awake again.