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

[Marc Zyngier <marc.zyngier@arm.com>]

On Thu, 5 May 2016 14:22:06 +0100
Jon Hunter <jonathanh@nvidia.com> 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@nvidia.com>
> >> Acked-by: Marc Zyngier <marc.zyngier@arm.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'?

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.

	M.
-- 
Jazz is not dead. It just smells funny.