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

[Jon Hunter]

On 05/05/16 14:40, Marc Zyngier wrote:
> On Thu, 5 May 2016 14:22:06 +0100
> Jon Hunter <jonathanh@xxxxxxxxxx> wrote:
> 
>> 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@xxxxxxxxxx>
>>>> Acked-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>>>> ---
>>>>  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'?
> 
> Yes, sorry.
> 
>>> (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.
> 
> I can squash this into your own patch if you're OK with it. I'll reply
> to your other patches shortly, as I have a number of comments there.

Yes that is fine with me.

Cheers
Jon