[v2,4/4] ARCv2: IRQ: Set a default priority for all core interrupts

After reset all interrupts in the core interrupt controller has
the highest priority P0. If the platform supports Fast IRQs and
has more than 1 banks of registers then CPU automatically switch
banks of registers when P0 interrupt comes.

The problem is that the kernel expects that by default switching
of banks is not used by all interrupts. It is necessary to set a
default nonzero priority for all available interrupts to avoid
undefined behaviour.

Signed-off-by: Yuriy Kolerov <yuriy.kolerov@synopsys.com>
---
 arch/arc/kernel/intc-arcv2.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

On 01/31/2017 03:45 AM, Yuriy Kolerov wrote:
> After reset all interrupts in the core interrupt controller has
> the highest priority P0. If the platform supports Fast IRQs and
> has more than 1 banks of registers then CPU automatically switch
> banks of registers when P0 interrupt comes.
> 
> The problem is that the kernel expects that by default switching
> of banks is not used by all interrupts. It is necessary to set a
> default nonzero priority for all available interrupts to avoid
> undefined behaviour.
> 
> Signed-off-by: Yuriy Kolerov <yuriy.kolerov@synopsys.com>
> ---
>  arch/arc/kernel/intc-arcv2.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arc/kernel/intc-arcv2.c b/arch/arc/kernel/intc-arcv2.c
> index 31246cc..d4fa4a5 100644
> --- a/arch/arc/kernel/intc-arcv2.c
> +++ b/arch/arc/kernel/intc-arcv2.c
> @@ -22,7 +22,7 @@
>   */
>  void arc_init_IRQ(void)
>  {
> -	unsigned int tmp, irq_prio;
> +	unsigned int tmp, irq_prio, i;
>  
>  	struct bcr_irq_arcv2 irq_bcr;
>  
> @@ -62,6 +62,16 @@ void arc_init_IRQ(void)
>  		irq_prio + 1, ARCV2_IRQ_DEF_PRIO,
>  		irq_bcr.firq ? " FIRQ (not used)":"");
>  
> +	/*
> +	 * Set a default priority for all available interrupts to prevent
> +	 * switching of register banks if Fast IRQ and multiple register banks
> +	 * are supported by CPU.
> +	 */
> +	for (i = NR_EXCEPTIONS; i < irq_bcr.irqs + NR_EXCEPTIONS; i++) {
> +		write_aux_reg(AUX_IRQ_SELECT, i);
> +		write_aux_reg(AUX_IRQ_PRIORITY, ARCV2_IRQ_DEF_PRIO);
> +	}
> +

This itself is fine. However going forward can we move to the genirq
irq_cpu_online() etc instead of doing this in our platform per cpu hook ?

https://www.linux-mips.org/archives/linux-mips/2011-03/msg00115.html


>  	/* setup status32, don't enable intr yet as kernel doesn't want */
>  	tmp = read_aux_reg(ARC_REG_STATUS32);
>  	tmp |= STATUS_AD_MASK | (ARCV2_IRQ_DEF_PRIO << 1);
>

Hi Vineet,

> -----Original Message-----
> From: Vineet Gupta [mailto:vgupta@synopsys.com]
> Sent: Tuesday, January 31, 2017 8:54 PM
> To: Yuriy Kolerov <yuriy.kolerov@synopsys.com>; linux-snps-
> arc@lists.infradead.org
> Cc: marc.zyngier@arm.com; Alexey.Brodkin@synopsys.com; linux-
> kernel@vger.kernel.org
> Subject: Re: [PATCH v2 4/4] ARCv2: IRQ: Set a default priority for all core
> interrupts
> 
> On 01/31/2017 03:45 AM, Yuriy Kolerov wrote:
> > After reset all interrupts in the core interrupt controller has the
> > highest priority P0. If the platform supports Fast IRQs and has more
> > than 1 banks of registers then CPU automatically switch banks of
> > registers when P0 interrupt comes.
> >
> > The problem is that the kernel expects that by default switching of
> > banks is not used by all interrupts. It is necessary to set a default
> > nonzero priority for all available interrupts to avoid undefined
> > behaviour.
> >
> > Signed-off-by: Yuriy Kolerov <yuriy.kolerov@synopsys.com>
> > ---
> >  arch/arc/kernel/intc-arcv2.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arc/kernel/intc-arcv2.c
> > b/arch/arc/kernel/intc-arcv2.c index 31246cc..d4fa4a5 100644
> > --- a/arch/arc/kernel/intc-arcv2.c
> > +++ b/arch/arc/kernel/intc-arcv2.c
> > @@ -22,7 +22,7 @@
> >   */
> >  void arc_init_IRQ(void)
> >  {
> > -	unsigned int tmp, irq_prio;
> > +	unsigned int tmp, irq_prio, i;
> >
> >  	struct bcr_irq_arcv2 irq_bcr;
> >
> > @@ -62,6 +62,16 @@ void arc_init_IRQ(void)
> >  		irq_prio + 1, ARCV2_IRQ_DEF_PRIO,
> >  		irq_bcr.firq ? " FIRQ (not used)":"");
> >
> > +	/*
> > +	 * Set a default priority for all available interrupts to prevent
> > +	 * switching of register banks if Fast IRQ and multiple register banks
> > +	 * are supported by CPU.
> > +	 */
> > +	for (i = NR_EXCEPTIONS; i < irq_bcr.irqs + NR_EXCEPTIONS; i++) {
> > +		write_aux_reg(AUX_IRQ_SELECT, i);
> > +		write_aux_reg(AUX_IRQ_PRIORITY, ARCV2_IRQ_DEF_PRIO);
> > +	}
> > +
> 
> This itself is fine. However going forward can we move to the genirq
> irq_cpu_online() etc instead of doing this in our platform per cpu hook ?
> 
> https://www.linux-mips.org/archives/linux-mips/2011-03/msg00115.html

We need to set a default priority for all interrupts for each CPU before interrupt controller is configured. In other words it this necessary to guaranty a default state of all interrupts before doing something else with interrupts. Moreover as I understand irq_cpu_online() is intended to be used with virtual IRQs (already allocated interrupts) but the configuration of priorities must be done for all hardware interrupts to bring CPU to the default state.

> >  	/* setup status32, don't enable intr yet as kernel doesn't want */
> >  	tmp = read_aux_reg(ARC_REG_STATUS32);
> >  	tmp |= STATUS_AD_MASK | (ARCV2_IRQ_DEF_PRIO << 1);
> >