netdev - Re: [PATCH net-next v3] net: dsa: mv88e6xxx: Prevent suspend to RAM

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Message-ID: <20190205112857.GB13620@t480s.localdomain>
Date:   Tue, 5 Feb 2019 11:28:57 -0500
From:   Vivien Didelot <vivien.didelot@...il.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Nadav Haklai <nadavh@...vell.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>
Subject: Re: [PATCH net-next v3] net: dsa: mv88e6xxx: Prevent suspend to RAM

Hi Miquel,

On Tue,  5 Feb 2019 12:07:28 +0100, Miquel Raynal <miquel.raynal@...tlin.com> wrote:

> +/* There is no suspend to RAM support at DSA level yet, the switch configuration
> + * would be lost after a power cycle so prevent it to be suspended.
> + */
> +static int __maybe_unused mv88e6xxx_suspend(struct device *dev)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static int __maybe_unused mv88e6xxx_resume(struct device *dev)
> +{
> +	return 0;
> +}

The code looks good but my only concern is -EOPNOTSUPP. In this
context this code is specific to callbacks targeting bridge and
switchdev, while the dev_pm_ops are completely parallel to DSA.

It is intuitive but given Documentation/power/runtime_pm.txt, this
will default to being interpreted as a fatal error, while -EBUSY
seems to keep the device in an 'active' state in a saner way.

I don't understand yet how to properly tell PM core that suspend to RAM
isn't supported. If an error code different from -EAGAIN or -EBUSY
is the way to go, I'm good with it:

Reviewed-by: Vivien Didelot <vivien.didelot@...il.com>

Thanks,

	Vivien