linux-kernel - Re: [PATCH] MIPS: Fix broken malta qemu

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Date:	Sat, 2 Apr 2016 13:19:03 +0100
From:	Qais Yousef <qsyousef@...il.com>
To:	Paul Burton <paul.burton@...tec.com>, ralf@...ux-mips.org
Cc:	Guenter Roeck <linux@...ck-us.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: Fix broken malta qemu

Hi Paul,

On 01/04/2016 13:48, Paul Burton wrote:
> On Thu, Mar 17, 2016 at 09:08:09PM +0000, Qais Yousef wrote:
>> Malta defconfig compiles with GIC on. Hence when compiling for SMP it causes the
>> new IPI code to be activated. But on qemu malta there's no GIC causing a
>> BUG_ON(!ipidomain) to be hit in mips_smp_ipi_init().
>>
>> Since in that configuration one can only run a single core SMP (!), skip IPI
>> initialisation if we detect that this is the case. It is a sensible behaviour
>> to introduce and should keep such possible configuration to run rather than die
>> hard unnecessarily.
> Hi Qais/Ralf,
>
> This patch is insufficient I'm afraid. It's entirely possible to use SMP
> with multiple VPEs in a single core on Malta boards that don't have a
> GIC - we have code handling IPIs in that case guarded by #ifdef
> CONFIG_MIPS_MT_SMP in arch/mips/mti-malta/malta-int.c. I think the
> BUG_ON needs to be removed entirely, unless that single-core multi-VPE
> IPI code is also converted to use an IPI irqdomain.
>

I was under the impression that SMP is only supported under GIC and 
older forms of SMP are deprecated.

I think the problem you're describing is different to the one this is 
trying to fix. The right fix for your issue is to make 
CONFIG_GENERIC_IRQ_IPI selected when CONFIG_MIPS_GIC && !CONFIG_MIPS_MT_SMP.

Would it be easy for you to create such a patch and test it?

Thanks,
Qais