[PATCH 1/1] irqchip: irq-gic: forward SGI to itself for cortex-a7 single core

[Peter Chen]

On Mon, Aug 08, 2016 at 02:39:35PM +0100, Marc Zyngier wrote:
> On Mon, 8 Aug 2016 15:49:54 +0800
> Peter Chen <peter.chen at nxp.com> wrote:
> 
> +Tony
> 
> > According to Cortex-A7 MPCore TRM, ch8.3.1, Distributor register summary,
> > GICD_ITARGETSRn:
> > 
> > 	The register that contains the SGI and PPI interrupts is
> >        	read-only and the value is implementation defined. For
> >        	Cortex-A7 configurations with only one processor, these
> >        	registers are RAZ/WI.
> > 
> > So, the GICD_ITARGETSR[0..7] is read-only, and the value is 0 for
> > cortex-a7 single core platform if the SoC is cortex-a7 mpcore version.
> > So the cupmask from gic_get_cpumask is 0.
> > 
> > At ARM Generic Interrupt Controller Architecture version 2.0,
> > ch4.3.15 Software Generated Interrupt Register, GICD_SGIR,
> > The distributor will process the requested SGI according to
> > register TargetListFilter and CPUTargetList. At current gic code,
> > it takes TargetListFilter as 0b00, and forward the interrupt to
> > cpumask (variable map at gic_raise_softirq) getting from gic_get_cpumask.
> > but cpumask is 0 according to above explanation for cortex-a7 single core
> > platform, so, both TargetListFilter and CPUTargetList are 0, and the
> > distributor does not forward the interrupt to any CPU interface according
> > to gic documentation, then the SGI can't be occurred.
> > 
> > We have found this problem at nxp imx6ul platform, which is a cortex-a7
> > single core platform, the irq work (triggered by SGI at ARM) can't be
> > occurred which is needed for cpufreq, then the system has failed to boot
> > and reboot [1].
> 
> I'm really not keep on this, as even if we paper over the problem for
> platforms using a GIC, we still leave behind all the platform that are
> not capable of self-IPI (which is the vast majority of ARM UP systems).
> 

This is a SMP system, not UP system, just cpu number is one.
Current problem is if we support self-IPI for SMP system, when the GIC
in this system doesn't have distribute interrupt capability.

> Can you please provide a backtrace of the failing use case? Have you
> tried this patch [1], which did solve the issue for OMAP?

This patch is for Feb, 2016, and I use the next-20160722, the related code
is at my kernel (although some other code at context is different).

-- 

Best Regards,
Peter Chen