linux-kernel - Re: [PATCH 01/16] ARM: scu: Provide support for parsing SCU device node to enable SCU

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Date:   Mon, 14 Nov 2016 14:51:43 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     linux-arm-kernel@...ts.infradead.org, Andrew Lunn <andrew@...n.ch>,
        Heiko Stuebner <heiko@...ech.de>, geert+renesas@...der.be,
        Linus Walleij <linus.walleij@...aro.org>,
        Liviu Dudau <liviu.dudau@....com>,
        Patrice Chotard <patrice.chotard@...com>,
        Wei Xu <xuwei5@...ilicon.com>,
        Jisheng Zhang <jszhang@...vell.com>,
        "pankaj.dubey" <pankaj.dubey@...sung.com>, magnus.damm@...il.com,
        Michal Simek <michal.simek@...inx.com>, krzk@...nel.org,
        thomas.ab@...sung.com, "cpgs ." <cpgs@...sung.com>,
        Stephen Warren <swarren@...dotorg.org>,
        Ray Jui <rjui@...adcom.com>, horms@...ge.net.au,
        Jun Nie <jun.nie@...aro.org>, shiraz.linux.kernel@...il.com,
        linux-kernel@...r.kernel.org, vireshk@...nel.org,
        Dinh Nguyen <dinguyen@...nsource.altera.com>,
        Shawn Guo <shawnguo@...nel.org>
Subject: Re: [PATCH 01/16] ARM: scu: Provide support for parsing SCU device
 node to enable SCU

On Mon, Nov 14, 2016 at 03:37:44PM +0100, Arnd Bergmann wrote:
> On Monday, November 14, 2016 1:50:18 PM CET Russell King - ARM Linux wrote:
> > On Mon, Nov 14, 2016 at 01:03:09PM +0100, Arnd Bergmann wrote:
> > > On Monday, November 14, 2016 2:10:16 PM CET pankaj.dubey wrote:
> > > > >> +    scu_base = of_iomap(np, 0);
> > > > >> +    of_node_put(np);
> > > > >> +    if (!scu_base) {
> > > > >> +            pr_err("%s failed to map scu_base via DT\n", __func__);
> > > > > 
> > > > > For non-ca5, non-ca9 based SoCs, we'll see this error msg. We understand
> > > > > what does it mean, but it may confuse normal users. In current version,
> > > > > berlin doesn't complain like this for non-ca9 SoCs
> > > > > 
> > > > 
> > > > OK, let me see other reviewer's comment on this. Then we will decide if
> > > > this error message is required or can be omitted.
> > > 
> > > We need to look at all callers here, to see if the function ever gets
> > > called for a CPU that doesn't have an SCU. I'd say we should warn if
> > > we know there is an SCU but we cannot map it, but never warn on
> > > any of the CPU cores that don't support an SCU.
> > 
> > Maybe there should be two helpers:
> > 
> > of_scu_enable() which _only_ looks up the SCU address in DT and enables
> > it if it finds it, otherwise returning failure.
> > 
> > a9_scu_enable() which tries to use the A9 provided SCU address and
> > enables it if it finds it, otherwise returning failure.
> > 
> > Then callers can decide which of these to call, and what error messages
> > to print on their failures.
> 
> Splitting the function in two is probably simpler overall, but
> we may still have to look at all the callers: Any platform that
> currently tries to map it on any CPU and doesn't warn about the
> absence of the device node (or about scu_a9_has_base() == false)
> should really continue not to warn about that.

Did you miss the bit where none of of_scu_enable() or a9_scu_enable()
should produce any warnings or errors to be printed.  It's up to the
caller to report the failure, otherwise doing this doesn't make sense:

	if (of_scu_enable() < 0 && a9_scu_enable() < 0)
		pr_err("Failed to map and enable the SCU\n");

because if of_scu_enable() prints a warning/error, then it's patently
misleading.

-- 
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