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 15:37:44 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        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 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.

If all platforms only call these on SMP machines with an
ARM11MPcore, Cortex-A5 or Cortex-A9, everything should be
fine here, otherwise we can leave the warning in the caller
after checking the return code of the new APIs.

	Arnd