linux-kernel - Re: [PATCH v2] arm: change vendor ID for virtio-mmio

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Date:	Fri, 31 Jul 2015 13:37:44 +0100
From:	Peter Maydell <peter.maydell@...aro.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	QEMU Developers <qemu-devel@...gnu.org>,
	Shannon Zhao <zhaoshenglong@...wei.com>,
	Igor Mammedov <imammedo@...hat.com>,
	Graeme Gregory <graeme.gregory@...aro.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alex Bennée <alex.bennee@...aro.org>
Subject: Re: [PATCH v2] arm: change vendor ID for virtio-mmio

On 29 July 2015 at 20:16, Michael S. Tsirkin <mst@...hat.com> wrote:
> ACPI spec 5.0 allows the use of PCI vendor IDs.
>
> Since we have one for virtio, it seems neater to use that
> rather than LNRO. For the device ID, use 103F which is a legacy ID that
> isn't used in virtio PCI spec - seems to make sense since virtio-mmio is
> a legacy device but we don't know the correct device type.
>
> Guests should probably match everything in the range 1000-103F
> (just like legacy pci drivers do) which will allow us to pass in the
> actual ID in the future if we want to.
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  hw/arm/virt-acpi-build.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index f365140..dea61ba 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -145,7 +145,7 @@ static void acpi_dsdt_add_virtio(Aml *scope,
>
>      for (i = 0; i < num; i++) {
>          Aml *dev = aml_device("VR%02u", i);
> -        aml_append(dev, aml_name_decl("_HID", aml_string("LNRO0005")));
> +        aml_append(dev, aml_name_decl("_HID", aml_string("1AF4103F")));
>          aml_append(dev, aml_name_decl("_UID", aml_int(i)));

So, I've just checked, and I believe that the kernel that RedHat
are shipping in their RHEL7 dev preview for AArch64 (and probably
thus also the Fedora/Centos one) includes a patch which adds
ACPI support to the virtio-mmio driver using the LNRO0005 ID string.

This to me suggests that we should just stick with that ID,
rather than changing to QEMUxxxx, the hex one based on the PCI
vendor ID, or anything else.

We're obviously under no obligation to make life easy for people
who ship kernels full of patches that haven't gone upstream yet,
but in this case there doesn't seem to me to be any benefit to
QEMU from picking an ID string that would break compatibility...

[The kernel I checked was the one in
https://git.centos.org/sources/kernel-aarch64/c7-aarch64/c589ab77889df6d93dbe817c373080631ab3275b
which despite the filename is actually an 80MB .tar.xz archive,
as pointed to by
https://git.centos.org/blob/rpms!kernel-aarch64/910dbce5f13419d68002f58e67ee6e762a93a425/.kernel-aarch64.metadata
]

thanks
-- PMM
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