linux-kernel - Re: [PATCH V2 03/10] irqchip,GICv3,ACPI: Add redistributor support via GICC structures.

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Message-ID: <56953471.5000505@semihalf.com>
Date:	Tue, 12 Jan 2016 18:14:25 +0100
From:	Tomasz Nowicki <tn@...ihalf.com>
To:	Marc Zyngier <marc.zyngier@....com>,
	Hanjun Guo <hanjun.guo@...aro.org>, tglx@...utronix.de,
	jason@...edaemon.net, rjw@...ysocki.net, lorenzo.pieralisi@....com,
	robert.richter@...iumnetworks.com, shijie.huang@....com,
	guohanjun@...wei.com, Suravee.Suthikulpanit@....com,
	"Chalamarla, Tirumalesh" <Tirumalesh.Chalamarla@...iumnetworks.com>
Cc:	mw@...ihalf.com, graeme.gregory@...aro.org,
	Catalin.Marinas@....com, will.deacon@....com,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, ddaney.cavm@...il.com
Subject: Re: [PATCH V2 03/10] irqchip,GICv3,ACPI: Add redistributor support
 via GICC structures.

On 12.01.2016 17:16, Marc Zyngier wrote:
>>> >>Also, the spec says:
>>> >>
>>> >>"On systems supporting GICv3 and above, this field holds the 64-bit
>>> >>physical address of the associated Redistributor. If all of the GIC
>>> >>Redistributors are in the always-on power domain, GICR structures should
>>> >>be used to describe the Redistributors instead, and this field must be
>>> >>set to 0."
>>> >>
>>> >>which triggers two questions:
>>> >>- Can you access always the GICR_TYPER register without waking the
>>> >>redistributor up?
>> >
>> >I missed this part, can you suggest how can we do that? accessing some
>> >register before access to redistributor?
> This redistributor may be in a power-domain that is off. Are you
> guaranteed that you can access GICR_TYPER even when it is off?
>
>> >
>>> >>- How do you cope with situations where some redistributors are in the
>>> >>always-on domain, and some are not?
>> >
>> >I'm not sure if there is such hardware, if yes, do we need to fix
>> >the spec first?
> It is something that should definitely be clarified. Can we end-up in a
> situation where some redistributors are described via the GICR
> structure, and some via the GICC structure? The spec is a bit ambiguous.
>

To recap:
1. GICR and GICC subtables should be mutually exclusive, but ACPI spec 
should be clear about this.
2. We need to know if we can access GICR_TYPER without waking the 
redistributor up.

Tirumalesh, can you please advice?

Tomasz