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

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Message-ID: <56FFD191.70606@roeck-us.net>
Date:	Sat, 2 Apr 2016 07:05:05 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Qais Yousef <qsyousef@...il.com>,
	Paul Burton <paul.burton@...tec.com>, ralf@...ux-mips.org
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: Fix broken malta qemu

On 04/02/2016 05:19 AM, Qais Yousef wrote:
> 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.
>
Didn't Paul say that his system doesn't have a GIC ? Are you saying that he can not
(or no longer) run an image built for SMP on his system ?

Guenter