Re: [PATCH] x86/apic: Update virtual irq base for DT/OF based system as well

[Andy Shevchenko]

On Wed, Aug 21, 2019 at 03:16:31PM +0200, Thomas Gleixner wrote:
> On Wed, 21 Aug 2019, Andy Shevchenko wrote:
> > On Wed, Aug 21, 2019 at 01:20:53PM +0200, Thomas Gleixner wrote:
> > > But x86 implements arch_dynirq_lower_bound() which overrides the core limit
> > > and because ioapic_dynirq_base is zero in the DT case it allows VIRQ 0 to
> > > be allocated which then causes of_irq*() to fail.
> > > 
> > > So your change prevents that by excluding the 'GSI' range from allocation,
> > > which means that the first irq number which is handed out is 24, assumed
> > > you have one IOAPIC with 24 pins.
> > 
> > I have tested this on the ACPI-based system where we have 55 lines of IOAPIC,
> > no PIC, and some GPIO lines. Overall I see that nr_irqs is 512 and shifting
> > by 55 freezes 10% of the space for nothing. Luckily we have SPARSE_IRQS
> > selected for any X86, so, it wouldn't waste memory.
> >
> > I think we may do slightly better if we just limit the change to the certain
> > cases.
> 
> For DT we can actually avoid that completely. See below.
> 
> For ACPI not unfortunately as the stupid GSI mapping is hard coded.

The below works better for my case, so, if you are going with that
Tested-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>

> 
> Thanks,
> 
> 	tglx
> 
> 8<-------------
> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -2438,7 +2438,13 @@ unsigned int arch_dynirq_lower_bound(uns
>  	 * dmar_alloc_hwirq() may be called before setup_IO_APIC(), so use
>  	 * gsi_top if ioapic_dynirq_base hasn't been initialized yet.
>  	 */
> -	return ioapic_initialized ? ioapic_dynirq_base : gsi_top;
> +	if (!ioapic_initialized)
> +		return gsi_top;
> +	/*
> +	 * For DT enabled machines ioapic_dynirq_base is irrelevant and not
> +	 * updated. So simply return @from if ioapic_dynirq_base == 0.
> +	 */
> +	return ioapic_dynirq_base ? : from;
>  }
>  
>  #ifdef CONFIG_X86_32

-- 
With Best Regards,
Andy Shevchenko