arm smp support patch

[Scott Valentine]

> On Tue, Nov 09, 2010 at 01:33:20PM -1000, Scott Valentine wrote:
>> On arm multi-core platforms that have a gic, the secondary cores fail to
>> wake if they are booted in WFI mode, as the gic_dist_init disables all
>> interrupts including IPI. I've included a simple patch to the
>> gic_dist_init function that enables interrupts 0-15 on SMP enabled
>> systems. This patch was made against linux-2.6-HEAD-151f52f.
>>
>>
>> diff -uNr a/arch/arm/common/gic.c b/arch/arm/common/gic.c
>> --- a/arch/arm/common/gic.c     2010-11-05 15:57:04.000000000 -1000
>> +++ b/arch/arm/common/gic.c     2010-11-09 13:08:33.000000000 -1000
>> @@ -262,6 +262,13 @@
>>         for (i = 0; i < max_irq; i += 32)
>>                 writel(0xffffffff, base + GIC_DIST_ENABLE_CLEAR + i * 4
>> /
>> 32);
>>
>> +#ifdef CONFIG_SMP
>> +       /*
>> +        * Enable IPI interrupts on SMP systems so we can wake secondary
>> cores
>> +        */
>> +       writel(0x0000ffff, base + GIC_DIST_ENABLE_SET);
>
> The ARM11 MPCore TRM [1] states "Interrupts 0-15 fields are read as one,
> that is, always enabled, and write to these fields have no effect."  So
> it seems odd that this is needed.  Errata?  FWIW, I've peeked and poked
> at GIC_DIST_ENABLE_SET and GIC_DIST_ENABLE_CLEAR via a debugger and the
> 16 LSBs of both of these registers are stuck-at-one on my ARM11 MPCore
> r1p0.

Okay, so I was wondering why this "bug" would be sitting around with so
many mpcore systems out in the field. It must be specific to the econa
3xxx processor (I'm working with a cns3420), as I can verify that the
second core fails to boot without the patch, but successfully boots with
it. The second core never gets past the wfi state in u-boot without this
patch.

Perhaps it the section should be wrapped with:

#if defined(MACH_CNS3XXX) && defined(SMP)

Can anyone else verify the behavior on the econa processor?

Thanks,
Scott V.

>
> --
> Regards,
> George
>
> [1]
> http://infocenter.arm.com/help/topic/com.arm.doc.ddi0360f/CCHGFFFA.html
>
>> +#endif
>> +
>>         /*
>>          * Setup the Linux IRQ subsystem.
>>          */
>>
>>
>>
>>
>>
>> NOTES:
>>
>> After browsing through the Kconfigs, I am confident that this will only
>> affect the following platforms (which have ARM_GIC and SMP):
>> MACH_REALVIEW, ARCH_OMAP4, ARCH_S5PV310, ARCH_VEXPRESS_CA9X4,
>> ARCH_U8500,
>> and ARCH_TEGRA_2x_SOC. The TEGRA_2x appears to use a diffent smp-boot
>> mechanism, however. The patch was tested successfully on MACH_CNS3XXX
>> using the bsp for the gateworks laguna platform
>> (http://svn.gateworks.com/bsp/laguna/trunk/openwrt_patches).
>>
>>
>> Scott Valentine
>>
>> Concentris Systems LLC
>> Manoa Innovation Center, Suite #238
>> 2800 Woodlawn Drive
>> Honolulu, HI  96822
>>
>> http://www.Concentris-Systems.com
>>
>> (808) 988-6100
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel at lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>


Scott Valentine

Concentris Systems LLC
Manoa Innovation Center, Suite #238
2800 Woodlawn Drive
Honolulu, HI  96822

http://www.Concentris-Systems.com

(808) 988-6100