Re: [PATCH v7 12/17] ARM64: ACPI: Check if it runs on Xen to enable or disable ACPI

From: Shannon Zhao <zhaoshenglong@huawei.com>
To: Mark Rutland <mark.rutland@arm.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Huangpeng (Peter)" <peter.huangpeng@huawei.com>,
	julien.grall@arm.com,
	Stefano Stabellini <stefano.stabellini@citrix.com>,
	Shannon Zhao <shannon.zhao@linaro.org>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	David Vrabel <david.vrabel@citrix.com>
Subject: Re: [PATCH v7 12/17] ARM64: ACPI: Check if it runs on Xen to enable or disable ACPI
Date: Fri, 1 Apr 2016 17:25:25 +0800	[thread overview]
Message-ID: <56FE3E85.60403__37117.4120381058$1459506339$gmane$org@huawei.com> (raw)
In-Reply-To: <20160331124216.GE26532@leverpostej>

On 2016/3/31 20:42, Mark Rutland wrote:
> On Thu, Mar 31, 2016 at 01:44:08PM +0200, Ard Biesheuvel wrote:
>> > The heuristic is there to decide whether some DTB image contains a
>> > complete description of the platform, or only some data handed over by
>> > the bootloader. Arguably, a DT containing both /chosen and /hypervisor
>> > but nothing else can still not describe an actual platform, and
>> > whether we execute under Xen or not is completely irrelevant.
> I disagree somewhat.
> 
> In general, a /hypervisor node may not be a Xen node, and could
> potentially imply some platform description. As /hypervisor is a generic
> name up for grabs by any hypervisor, we simply cannot make assumptions
> about it.
> 
> As /chosen is a special reserved path that implies a particular binding
> and has no compatible string, so checking its path alone is correct.
> 
> While we do check that the /hypervisor node is "xen,xen" compatible
> elsewhere, the canonical mechanism of checking for a Xen node (as
> opposed to any hypervisor's node) is to check the compatible string.
> 
> If we are going to handle nodes for other hypervisors while treating the
> DTB as empty, we need code and discussion regarding said hypervisor.
> 
> Hence, for checking for a Xen /hypervisor node, I would prefer we
> checked the compatible string rather than the path.
> 
> An is_xen_node() helper (which could also check that the path is
> "/hypervisor") would avoid having redundant, subtly distinct ways of
> checking, and would explicitly document precisely what we are checking
> for.

So if we use is_xen_node(), do we need to call xen_initial_domain()
again? I still think here is_xen_node() and xen_initial_domain() have
same meaning. Why do we need that?

If it really needs is_xen_node(), I will not factor
fdt_find_hyper_node() in patch 11 since it uses flat DT while here it's
going to use unflatten DT.

Thanks,
-- 
Shannon

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