linux-kernel - Re: [PATCH v3 3/5] arm64: dts: Add support for Spreadtrum SC9836 SoC in dts and Makefile

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Message-ID: <20141128144412.GG7144@arm.com>
Date:	Fri, 28 Nov 2014 14:44:12 +0000
From:	Will Deacon <will.deacon@....com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	"andrew@...n.ch" <andrew@...n.ch>,
	"heiko@...ech.de" <heiko@...ech.de>,
	"gnomes@...rguk.ukuu.org.uk" <gnomes@...rguk.ukuu.org.uk>,
	Chunyan Zhang <chunyan.zhang@...eadtrum.com>,
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Subject: Re: [PATCH v3 3/5] arm64: dts: Add support for Spreadtrum SC9836 SoC
 in dts and Makefile

On Fri, Nov 28, 2014 at 02:35:32PM +0000, Mark Rutland wrote:
> On Fri, Nov 28, 2014 at 02:29:13PM +0000, Catalin Marinas wrote:
> > On Thu, Nov 27, 2014 at 01:43:09PM +0000, Mark Rutland wrote:
> > > On Thu, Nov 27, 2014 at 12:12:15PM +0000, Catalin Marinas wrote:
> > > > On Thu, Nov 27, 2014 at 11:50:43AM +0000, Mark Rutland wrote:
> > > > > On Tue, Nov 25, 2014 at 12:16:56PM +0000, Chunyan Zhang wrote:
> > > > > > +
> > > > > > +       timer {
> > > > > > +               compatible = "arm,armv8-timer";
> > > > > > +               interrupts = <1 13 0xff01>,
> > > > > > +                            <1 14 0xff01>,
> > > > > > +                            <1 11 0xff01>,
> > > > > > +                            <1 10 0xff01>;
> > > > > > +               clock-frequency = <26000000>;
> > > > > 
> > > > > Please remove the clock-frequency property. Your FW should initialise
> > > > > CNTFRQ_EL0 on all CPUs (certainly PSCI 0.2 requires that you do this).
> > > > 
> > > > Since this comes up regularly, I think we need a dev_warn() in the arch
> > > > timer driver when CONFIG_ARM64.
> > > 
> > > I'll ack such a patch ;)
> > 
> > How rude would this be?
> > 
> > diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> > index 2133f9d59d06..aaaf3433ccb9 100644
> > --- a/drivers/clocksource/arm_arch_timer.c
> > +++ b/drivers/clocksource/arm_arch_timer.c
> > @@ -371,7 +371,8 @@ arch_timer_detect_rate(void __iomem *cntbase, struct device_node *np)
> > 		return;
> >  
> > 	/* Try to determine the frequency from the device tree or CNTFRQ */
> > -	if (of_property_read_u32(np, "clock-frequency", &arch_timer_rate)) {
> > +	if (IS_ENABLED(CONFIG_ARM64) ||
> > +	    of_property_read_u32(np, "clock-frequency", &arch_timer_rate)) {
> > 		if (cntbase)
> > 			arch_timer_rate = readl_relaxed(cntbase + CNTFRQ);
> > 		else
> >
> 
> Probably too rude, given it doesn't WARN() the user.

We override broken hardware ID registers all the time in device-tree without
dumping stack. Why is this any different?

> We should be extremely loud if we see the clock-frequency property on an
> arm64 system. Whether or not we should ignore the property is another
> matter.

I don't really see the point in ignoring it. We will see broken hardware
[1] and this is just preventing ourselves from working around it. I'd much
rather have arch-timers with a "clock-frequence" property than have some
other timer instead because the kernel driver is being stubborn.

Will

[1] A previous version of the Juno firmware, for example.
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