linux-kernel - Re: [PATCH 2/3] arm64: dts: add the Alpine v2 EVP

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Date:	Tue, 9 Feb 2016 09:30:29 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Tsahee Zidenberg <tsahee@...apurnalabs.com>
Cc:	Antoine Tenart <antoine.tenart@...e-electrons.com>,
	catalin.marinas@....com, will.deacon@....com,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Ronen Shitrit <rshitrit@...apurnalabs.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Barak Wasserstrom <barak@...apurnalabs.com>
Subject: Re: [PATCH 2/3] arm64: dts: add the Alpine v2 EVP

On 09/02/16 09:14, Tsahee Zidenberg wrote:
> 
> 
> On 9 February 2016 at 11:09, Marc Zyngier <marc.zyngier@....com
> <mailto:marc.zyngier@....com>> wrote:
> 
>     On 09/02/16 09:01, Antoine Tenart wrote:
>     > On Tue, Feb 09, 2016 at 09:56:33AM +0100, Antoine Tenart wrote:
>     >> Hi Marc,
>     >>
>     >> On Mon, Feb 08, 2016 at 03:29:33PM +0000, Marc Zyngier wrote:
>     >>> On 08/02/16 09:11, Antoine Tenart wrote:
>     >>>
>     >>>> +          gic: gic@...00000 {
>     >>>> +                  compatible = "arm,gic-v3";
>     >>>> +                  reg = <0x0 0xf0200000 0x0 0x10000>,     /* GIC Dist */
>     >>>> +                        <0x0 0xf0280000 0x0 0x200000>,    /* GICR */
>     >>>> +                        <0x0 0xf0100000 0x0 0x2000>;      /* GICC */
>     >>>> +                  interrupt-controller;
>     >>>> +                  #interrupt-cells = <3>;
>     >>>> +          };
>     >>>
>     >>> Something is wrong here. Either you are missing GICH and GICV (assuming
>     >>> you have legacy support), or you have an extra GICC region (which
>     >>> doesn't make sense on its own).
>     >>
>     >> I'll add the missing regions.
>     >
>     > Hmm, in fact the GICC region shouldn't be there. I'll make some tests
>     > and remove it.
> 
>     If you have a GICv3 with legacy support, you will probably have GICC,
>     GICH and GICV. Linux itself will only use GICD and GICR, but it needs at
>     least GICV to be able to virtualize GICv2 guests. And GICV is not
>     allowed to exist without GICC and GICH, so I really recommend that you
>     keep GICC around.
> 
> 
> We use the GIC without legacy support (we disable it in early boot
> stages), so I think removing the GICC region is the better solution.

Disabling legacy support doesn't mean that:
- the HW isn't present
- the associated regions are not useful

Here, we describe the HW, not the usage you make of it.

And unless you think that having working virtualization is completely
useless, I strongly suggest that you properly document the HW in the
device tree.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...