netdev - Re: [PATCH v2] ravb: add wake-on-lan support via magic packet

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Date:   Sun, 30 Jul 2017 22:19:29 +0200
From:   Niklas Söderlund 
        <niklas.soderlund@...natech.se>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH v2] ravb: add wake-on-lan support via magic packet

Hi Andrew,

On 2017-07-30 22:07:31 +0200, Andrew Lunn wrote:
> On Sun, Jul 30, 2017 at 09:51:54PM +0200, Niklas Söderlund wrote:
> > Hi Andrew,
> > 
> > On 2017-07-30 19:07:38 +0200, Andrew Lunn wrote:
> > > Hi Niklas
> > > 
> > > > @@ -2041,6 +2073,11 @@ static int ravb_probe(struct platform_device *pdev)
> > > >  
> > > >  	priv->chip_id = chip_id;
> > > >  
> > > > +	/* Get clock, if not found that's OK but Wake-On-Lan is unavailable */
> > > > +	priv->clk = devm_clk_get(&pdev->dev, NULL);
> > > > +	if (IS_ERR(priv->clk))
> > > > +		priv->clk = NULL;
> > > 
> > > Can you get EPROBE_DEFER returned?
> > 
> > I don't think so, but I'm not sure :-)
> > 
> > The clock I'm trying to get is the module clock of the ravb itself, so 
> > if that clock is not available (and enabled) no register writes to the 
> > ravb would be possible in the first place, so i guess it's safe to 
> > assume -EPROBE_DEFER can not happen here?
> > 
> > I'm just trying to play it safe here since the clock is only needed to 
> > support WoL, I though it best to not change behavior here. Try to get 
> > the clock, if we can great we can do WoL if not then user-space will be 
> > prevented from enabling WoL and nothing in the current behavior changes.
> 
> Hi Nikls
> 
> Well, if it can return -EPROBE_DEFER, it means sometimes WoL will be
> avalable and other times not, depending on when the clock driver

Ahh I see yes that would be indeed be bad.

> probes. However, it sounds like this is the SoCs core clock driver. If
> so, it gets loaded very early, so you are safe.

Yes this is renesas-cpg-mssr which if I understand things is a core 
clock driver. It is register in drivers/clk/renesas/renesas-cpg-mssr.c 
using:

 subsys_initcall(cpg_mssr_init);

So I take it I'm safe. Thanks however for bringing this to my attention 
I learnt something new today :-)

> 
>        Andrew

-- 
Regards,
Niklas Söderlund