linux-kernel - Re: [PATCH v7 1/3] irqchip/gic-v3-its: add ability to save/restore ITS state

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Message-ID: <20180301114144.nmwu4qtslvj7ogj5@lakrids.cambridge.arm.com>
Date:   Thu, 1 Mar 2018 11:41:45 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Derek Basehore <dbasehore@...omium.org>
Cc:     linux-kernel@...r.kernel.org, Soby.Mathew@....com,
        sudeep.holla@....com, devicetree@...r.kernel.org,
        robh+dt@...nel.org, linux-pm@...r.kernel.org,
        rafael.j.wysocki@...el.com, tglx@...utronix.de,
        briannorris@...omium.org, marc.zyngier@....com
Subject: Re: [PATCH v7 1/3] irqchip/gic-v3-its: add ability to save/restore
 ITS state

On Wed, Feb 28, 2018 at 09:48:18PM -0800, Derek Basehore wrote:
> Some platforms power off GIC logic in suspend, so we need to
> save/restore state. The distributor and redistributor registers need
> to be handled in platform code due to access permissions on those
> registers, but the ITS registers can be restored in the kernel.
> 
> Signed-off-by: Derek Basehore <dbasehore@...omium.org>

How much state do we have to save/restore?

Given we can apparently read all this state, couldn't we *always* save
the state, then upon resume detect if the state has been lost, restoring
it if so?

That way, we don't need a property in FW tables for DT or ACPI.

[...]

> @@ -3261,6 +3363,9 @@ static int __init its_probe_one(struct resource *res,
>  		ctlr |= GITS_CTLR_ImDe;
>  	writel_relaxed(ctlr, its->base + GITS_CTLR);
>  
> +	if (fwnode_property_present(handle, "reset-on-suspend"))
> +		its->flags |= ITS_FLAGS_SAVE_SUSPEND_STATE;

Does this allow this property on an ACPI system?

If we need this on ACPI, we need a spec update to handle this properly,
and shouldn't use device properties like this.

Thanks,
Mark.