linux-kernel - Re: [RFC PATCH 3/9] irqchip: GIC: Convert to EOImode == 1

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Date:	Wed, 25 Jun 2014 09:08:27 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Anup Patel <anup@...infault.org>
Cc:	Marc Zyngier <marc.zyngier@....com>,
	Ian Campbell <ian.campbell@...rix.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 3/9] irqchip: GIC: Convert to EOImode == 1

On Wed, Jun 25, 2014 at 8:56 AM, Anup Patel <anup@...infault.org> wrote:
> Hi Marc,
>
> On Wed, Jun 25, 2014 at 2:58 PM, Marc Zyngier <marc.zyngier@....com> wrote:
>> So far, GICv2 has been used in with EOImode == 0. The effect of this
>> mode is to perform the priority drop and the deactivation of the
>> interrupt at the same time.
>>
>> While this works perfectly for Linux (we only have a single priority),
>> it causes issues when an interrupt is forwarded to a guest, and when
>> we want the guest to perform the EOI itself.
>>
>> For this case, the GIC architecture provides EOImode == 1, where:
>> - A write to the EOI register drops the priority of the interrupt and leaves
>> it active. Other interrupts at the same priority level can now be taken,
>> but the active interrupt cannot be taken again
>> - A write to the DIR marks the interrupt as inactive, meaning it can
>> now be taken again.
>>
>> We only enable this feature when booted in HYP mode. Also, as most device
>> trees are broken (they report the CPU interface size to be 4kB, while
>> the GICv2 CPU interface size is 8kB), output a warning if we're booted
>> in HYP mode, and disable the feature.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
>> ---

[...]

>> +               if (resource_size(&cpu_res) >= SZ_8K)
>> +                       supports_deactivate = true;
>> +               else
>> +                       pr_warn("GIC: CPU interface size is %x, DT is probably wrong\n", (int)resource_size(&cpu_res));
>
> This will not work on APM X-Gene because, for
> X-Gene first CPU page is at 0x78020000 and
> second CPU page is at 0x78030000.

Does 0x7802f000 for the cpu address not work? It should if X-Gene is
"SBSA compliant" for whatever that is worth.

Rob
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