linux-kernel - Re: [PATCH 1/3] irqchip/GIC: Add workaround for aliased GIC400

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Date:	Fri, 22 Jan 2016 15:25:23 -0800
From:	Duc Dang <dhdang@....com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Pavel Fedin <p.fedin@...sung.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Stuart Yoder <stuart.yoder@...escale.com>,
	Julien Grall <julien.grall@...rix.com>,
	linux-arm <linux-arm-kernel@...ts.infradead.org>,
	patches <patches@....com>
Subject: Re: [PATCH 1/3] irqchip/GIC: Add workaround for aliased GIC400

On Wed, Jan 20, 2016 at 1:06 AM, Marc Zyngier <marc.zyngier@....com> wrote:
> Hi Duc,
>
> On Tue, 19 Jan 2016 11:12:15 -0800
> Duc Dang <dhdang@....com> wrote:
>
>> On Sun, Sep 13, 2015 at 4:14 AM, Marc Zyngier <marc.zyngier@....com> wrote:
>> >
>> > The GICv2 architecture mandates that the two 4kB GIC regions are
>> > contiguous, and on two separate physical pages (so that access to
>> > the second page can be trapped by a hypervisor). This doesn't work
>> > very well when PAGE_SIZE is 64kB.
>> >
>> > A relatively common hack^Wway to work around this is to alias each
>> > 4kB region over its own 64kB page. Of course in this case, the base
>> > address you want to use is not really the begining of the region,
>> > but base + 60kB (so that you get a contiguous 8kB region over two
>> > distinct pages).
>> >
>> > Normally, this would be described in DT with a new property, but
>> > some HW is already out there, and the firmware makes sure that
>> > it will override whatever you put in the GIC node. Duh. And of course,
>> > said firmware source code is not available, despite being based
>> > on u-boot.
>> >
>> > The workaround is to detect the case where the CPU interface size
>> > is set to 128kB, and verify the aliasing by checking that the ID
>> > register for GIC400 (which is the only GIC wired this way so far)
>> > is the same at base and base + 0xF000. In this case, we update
>> > the GIC base address and let it roll.
>>
>> Hi Marc,
>>
>> When booting ACPI with X-Gene Mustang, I saw it hangs when EOI mode is
>> enabled, should we have ACPI version for gic_check_eoimode as well?
>
> ACPI doesn't provide the size of the CPU interface, so you cannot
> perform the same kind of check and bug workaround. I'm afraid you have
> to fix your ACPI tables (which shouldn't be a problem since nobody is
> using ACPI in production so far...).
>
Thanks, Marc.

We will go with your suggestion.

Regards,
Duc Dang.
> Thanks,
>
>         M.
> --
> Jazz is not dead. It just smells funny.