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Date: Fri, 28 Nov 2014 15:09:12 +0000
From: Will Deacon <will.deacon@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <Mark.Rutland@arm.com>, "andrew@lunn.ch" <andrew@lunn.ch>,
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Subject: Re: [PATCH v3 3/5] arm64: dts: Add support for Spreadtrum SC9836 SoC
 in dts and Makefile
Message-ID: <20141128150912.GI7144@arm.com>
References: <Sharkl64-v3>
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 <20141127115042.GE857@leverpostej>
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 <20141128142913.GB5393@localhost>
 <20141128143532.GI25883@leverpostej>
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On Fri, Nov 28, 2014 at 03:03:26PM +0000, Catalin Marinas wrote:
> On Fri, Nov 28, 2014 at 02:44:12PM +0000, Will Deacon wrote:
> > 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?
> 
> I'm not for dumping the stack, it's not relevant (just more noise).
> 
> > > 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.
> 
> I agree that sooner or later we'll need a workaround (we already did for
> Juno). My point is that many consider such overriding behaviour to be
> the default - i.e. don't bother writing any sane value in CNTFRQ in
> firmware at boot because Linux can cope without. It gets worse when
> companies develop their firmware long before starting to upstream kernel
> patches, so too late to fix it.
> 
> > [1] A previous version of the Juno firmware, for example.
> 
> What about CONFIG_BROKEN_FIRMWARE, default off?

I'd rather have a `firmware test' module, which could be as noisy as it
likes when it finds issues like this. It could also do things like fuzz the
PSCI interface.

> In the meantime I think we can be more tolerant:
> 
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 2133f9d59d06..87f67a93fcc7 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -376,6 +376,8 @@ arch_timer_detect_rate(void __iomem *cntbase, struct device_node *np)
>  			arch_timer_rate = readl_relaxed(cntbase + CNTFRQ);
>  		else
>  			arch_timer_rate = arch_timer_get_cntfrq();
> +	} else if (IS_ENABLED(CONFIG_ARM64)) {
> +		pr_warn("Architected timer frequency overridden by DT (broken firmware?)\n");
>  	}

That looks sensible. It would be interesting to print the value of CNTFRQ
too.

Will
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