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

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Message-ID: <20190205194723.6d567b4e@xps13>
Date:   Tue, 5 Feb 2019 19:47:23 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Vivien Didelot <vivien.didelot@...il.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>
Subject: Re: [PATCH net-next v3] net: dsa: mv88e6xxx: Prevent suspend to RAM

Hi Vivien,

Vivien Didelot <vivien.didelot@...il.com> wrote on Tue, 5 Feb 2019
11:28:57 -0500:

> 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:

I do share your concern and I went through the Documentation but I did
not find a unified way to tell the PM core the feature is unsupported.

By grepping code, I realized returning -EOPNOTSUPP was a recurrent
alternative so here we are. I also considered -EBUSY but it seems more
like a "I cannot right now" and -EAGAIN which is more a "try again
soon". Anyway, no matter the error code returned, I'm not sure if the PM
core actually cares?
 
> Reviewed-by: Vivien Didelot <vivien.didelot@...il.com>
> 
> 
> Thanks,
> 
> 	Vivien


Thanks,
Miquèl