linux-kernel - Re: [PATCH V3 02/17] irqchip/gic: WARN if setting the interrupt type for a PPI fails

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Date:	Thu, 5 May 2016 14:22:06 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Marc Zyngier <marc.zyngier@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Rob Herring <robh+dt@...nel.org>,
	"Pawel Moll" <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"Stephen Warren" <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>
CC:	Kevin Hilman <khilman@...nel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	<linux-tegra@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 02/17] irqchip/gic: WARN if setting the interrupt type
 for a PPI fails

Hi Marc,

On 05/05/16 13:06, Marc Zyngier wrote:
> Hi Jon,
> 
> On 04/05/16 17:25, Jon Hunter wrote:
>> Setting the interrupt type for private peripheral interrupts (PPIs) may
>> not be supported by a given GIC because it is IMPLEMENTATION DEFINED
>> whether this is allowed. There is no way to know if setting the type is
>> supported for a given GIC and so the value written is read back to
>> verify it matches the desired configuration. If it does not match then
>> an error is return.
>>
>> There are cases where the interrupt configuration read from firmware
>> (such as a device-tree blob), has been incorrect and hence
>> gic_configure_irq() has returned an error. This error has gone
>> undetected because the error code returned was ignored but the interrupt
>> still worked fine because the configuration for the interrupt could not
>> be overwritten.
>>
>> Given that this has done undetected and that failing to set the
>> configuration for a PPI may not be a catastrophic, don't return an error
>> but WARN if we fail to configure a PPI. This will allows us to fix up
>> any places in the kernel where we should be checking the return status
>> and maintain backward compatibility with firmware images that may have
>> incorrect PPI configurations.
>>
>> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
>> Acked-by: Marc Zyngier <marc.zyngier@....com>
>> ---
>>  drivers/irqchip/irq-gic-common.c | 11 +++++++----
>>  1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-gic-common.c b/drivers/irqchip/irq-gic-common.c
>> index ffff5a45f1e3..9fa92a17225c 100644
>> --- a/drivers/irqchip/irq-gic-common.c
>> +++ b/drivers/irqchip/irq-gic-common.c
>> @@ -56,12 +56,15 @@ int gic_configure_irq(unsigned int irq, unsigned int type,
>>  
>>  	/*
>>  	 * Write back the new configuration, and possibly re-enable
>> -	 * the interrupt. If we fail to write a new configuration,
>> -	 * return an error.
>> +	 * the interrupt. WARN if we fail to write a new configuration
>> +	 * and return an error if we failed to write the configuration
>> +	 * for an SPI. If we fail to write the configuration for a PPI
>> +	 * this is most likely because the GIC does not allow us to set
>> +	 * the configuration and so it is not a catastrophic failure.
>>  	 */
>>  	writel_relaxed(val, base + GIC_DIST_CONFIG + confoff);
>> -	if (readl_relaxed(base + GIC_DIST_CONFIG + confoff) != val)
>> -		ret = -EINVAL;
>> +	if (WARN_ON(readl_relaxed(base + GIC_DIST_CONFIG + confoff) != val))
>> +		ret = irq < 32 ? 0 : -EINVAL;
>>  
>>  	if (sync_access)
>>  		sync_access();
>>
> 
> I'm going to slightly backpedal on that one:
> 
> When running in non-secure mode, you can reconfigure secure interrupts

Do you mean 'cannot'?

> (for obvious reasons). But you don't know which mode you're running in
> either. A typical example is the arch timer, which requests both secure
> and non-secure interrupts, because we cannot know which side of the CPU
> we're running on. In the non-secure case, we end-up with a splat that
> is rather undeserved.

Yes seems sensible.

> So I'm tempted to tone down the splat in the PPI case like this:
> 
> diff --git a/drivers/irqchip/irq-gic-common.c b/drivers/irqchip/irq-gic-common.c
> index 083c303..1605e42 100644
> --- a/drivers/irqchip/irq-gic-common.c
> +++ b/drivers/irqchip/irq-gic-common.c
> @@ -63,8 +63,17 @@ int gic_configure_irq(unsigned int irq, unsigned int type,
>  	 * the configuration and so it is not a catastrophic failure.
>  	 */
>  	writel_relaxed(val, base + GIC_DIST_CONFIG + confoff);
> -	if (WARN_ON(readl_relaxed(base + GIC_DIST_CONFIG + confoff) != val))
> -		ret = irq < 32 ? 0 : -EINVAL;
> +	oldval = readl_relaxed(base + GIC_DIST_CONFIG + confoff);
> +	if (oldval != val) {
> +		if (irq < 32) {
> +			pr_warn("GIC: PPI%d is either secure or misconfigured\n",
> +				irq - 16);
> +			ret = 0;
> +		} else {
> +			WARN_ON(1);
> +			ret = -EINVAL;
> +		}
> +	}
>  
>  	if (sync_access)
>  		sync_access();
> 
> Thoughts?

That is fine with me. Do you want me to re-spin or do you want to apply
your change on top? However, before I re-spin would like to get your
thoughts on patches 13-17.

Cheers
Jon