[PATCH v2] ARM: gic: fix irq_alloc_descs handling for sparse irq

[Rob Herring]

Magnus,

On 11/14/2011 07:19 AM, Magnus Damm wrote:
> On Mon, Oct 24, 2011 at 11:36 PM, Rob Herring <robherring2 at gmail.com> wrote:
>> From: Rob Herring <rob.herring at calxeda.com>
>>
>> Commit "ARM: gic: add irq_domain support" (2071a2a4b8ed5292) broke SPARSE_IRQ
>> on platforms with GIC. When SPARSE_IRQ is enabled, all NR_IRQS or
>> mach_desc->nr_irqs will be allocated by arch_probe_nr_irqs(). This caused
>> irq_alloc_descs to allocate irq_descs after the pre-allocated space.
>>
>> Make irq_alloc_descs search for an exact irq range and assume it has
>> been pre-allocated on failure. For DT probing dynamic allocation is used.
>> DT enabled platforms should set their nr_irqs to NR_IRQ_LEGACY and have all
>> irq_chips allocate their irq_descs with irq_alloc_descs if SPARSE_IRQ is
>> enabled.
>>
>> gic_init irq_start param is changed to be signed with negative meaning do
>> dynamic Linux irq assigment.
>>
>> Signed-off-by: Rob Herring <rob.herring at calxeda.com>
>> ---
>> v2:
>>  - make irq_start signed
> 
> Hi Rob,
> 
> [Added Paul Mundt as CC]
> 
> Thanks for your work on improving the GIC code. I tested latest 3.2-rc
> on some of our GIC platforms without DT earlier today and I ran into
> some issues that I believe are related to the following commit:
> 
> f37a53c ARM: gic: fix irq_alloc_descs handling for sparse irq
> 
> With this patch included I get the following warning on SH-Mobile
> AG5EVM and Kota2:
> 
> NR_IRQS:1024 nr_irqs:1024 1024
> ------------[ cut here ]------------
> WARNING: at arch/arm/common/gic.c:607 gic_init+0x90/0x2e4()
> Cannot allocate irq_descs @ IRQ16, assuming pre-allocated
> [<c000c868>] (unwind_backtrace+0x0/0xe0) from [<c001857c>] (warn_slowpath_commo)
> [<c001857c>] (warn_slowpath_common+0x48/0x60) from [<c00185d8>] (warn_slowpath_)
> [<c00185d8>] (warn_slowpath_fmt+0x2c/0x3c) from [<c029ee08>] (gic_init+0x90/0x2)
> [<c029ee08>] (gic_init+0x90/0x2e4) from [<c029f278>] (sh73a0_init_irq+0x30/0x18)
> [<c029f278>] (sh73a0_init_irq+0x30/0x184) from [<c029c0b4>] (init_IRQ+0x14/0x1c)
> [<c029c0b4>] (init_IRQ+0x14/0x1c) from [<c029a5cc>] (start_kernel+0x15c/0x2b8)
> [<c029a5cc>] (start_kernel+0x15c/0x2b8) from [<4000803c>] (0x4000803c)
> ---[ end trace 1b75b31a2719ed1c ]---
> 
> The sh73a0 used on the AG5EVM board has a bunch of interrupt
> controllers, but the GIC is initialized first.
> 
> As you can see by the printout above "nr_irqs" is set to 1024, but I
> believe this may be a misconfiguration on my side. Or perhaps it's the
> ARM default that needs to be adjusted, because it's certainly not
> behaving like other architectures such as x86 and SH.
> 
> The x86 and SH implementations of sparse IRQ seem to return
> NR_IRQS_LEGACY from arch_probe_nr_irqs(), but on ARM we default to
> NR_IRQS unless the machine descriptor gives a different hint.
> 

Yes, the ARM version definitely seems wrong to me.

> I could easily "fix" my platform by making it behave like x86 and SH:
> --- 0001/arch/arm/mach-shmobile/board-ag5evm.c
> +++ work/arch/arm/mach-shmobile/board-ag5evm.c	2011-11-14
> 21:45:24.000000000 +0900
> @@ -607,6 +607,7 @@ struct sys_timer ag5evm_timer = {
> 
>  MACHINE_START(AG5EVM, "ag5evm")
>  	.map_io		= ag5evm_map_io,
> +	.nr_irqs	= NR_IRQS_LEGACY,
>  	.init_irq	= sh73a0_init_irq,
>  	.handle_irq	= shmobile_handle_irq_gic,
>  	.init_machine	= ag5evm_init,
> 
> The above code makes sure that only 16 interrupts are reserved early
> on, so the warning disappears and the nr_irqs is different:
> NR_IRQS:1024 nr_irqs:16 16
> 

For now, this is the correct fix. shmobile is the only platform that
uses sparse irqs and correctly calls irq_alloc_descs.

> I do however wonder if the ARM default is sane. Perhaps it is, but
> just to experiment I decided to modify the common ARM code like this:
> --- 0001/arch/arm/kernel/irq.c
> +++ work/arch/arm/kernel/irq.c	2011-11-14 22:06:02.000000000 +0900
> @@ -130,7 +130,7 @@ void __init init_IRQ(void)
>  int __init arch_probe_nr_irqs(void)
>  {
>  	nr_irqs = machine_desc->nr_irqs ? machine_desc->nr_irqs : NR_IRQS;
> -	return nr_irqs;
> +	return NR_IRQS_LEGACY;
>  }
>  #endif
> 
> With the patch above the warning printout is disappeared and the
> nr_irqs message is slightly different:
> NR_IRQS:1024 nr_irqs:1024 16

Something like this was my initial fix, but that would pretty much break
sparse irq on every platform except shmobile. All the irq_chip
implementations need to be converted to use irqdomains and call have
calls to irq_alloc_descs (or perhaps we move that into irqdomain code).
There's around 50 implementations in arch/arm...

> 
> I don't really have any strong feelings exactly how to fix this, but I
> suspect that other non-DT GIC-enabled platforms will run into the same
> problem unless they set .nr_irqs in their machine descriptor table.
> 

I think shmobile is the only platform with sparse irq on by default with
a GIC.

Rob