Linux Virtualization - Jul 2015 - [PATCH v2] arm: change vendor ID for virtio-mmio

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 at redhat.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)));
 
         Aml *crs = aml_resource_template();
-- 
MST

On 2015/7/30 3:16, Michael S. Tsirkin wrote:
> ACPI spec 5.0 allows the use of PCI vendor IDs.
> 
But virtio-mmio is not a PCI device, it's a platform device.
Why do we drop the previous way using "QEMUXXXX"? Something I missed?
> 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 at redhat.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)));
>  
>          Aml *crs = aml_resource_template();
> 
-- 
Shannon

On Thu, Jul 30, 2015 at 09:23:20AM +0800, Shannon Zhao
wrote:
> 
> 
> On 2015/7/30 3:16, Michael S. Tsirkin wrote:
> > ACPI spec 5.0 allows the use of PCI vendor IDs.
> > 
> But virtio-mmio is not a PCI device, it's a platform device.
Yes. ACPI spec 5.0 says:

	A valid PNP ID must be of the form "AAA####" where A is an uppercase
	letter and # is a hex digit. A valid ACPI ID must be of the form
	"NNNN####" where N is an uppercase letter or a digit
('0'-'9') and # is
	a hex digit. This specification reserves the string "ACPI" for use
only
	with devices defined herein.

	It further reserves all strings representing 4 HEX digits for
	exclusive use with PCI-assigned Vendor IDs.

The second paragraph means if PCI SIG assigned you an ID, you
can use that without need to register it with ASWG.

> Why do we drop the previous way using "QEMUXXXX"? Something I
missed?
So that guests that bind to this interface will work fine with non QEMU
implementations of virtio-mmio.

It's just playing nice with others.

We could have done something similar to pvpanic as well, except we
didn't and guests using the QEMU prefix have been released,
so we have to keep using that.
> > 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 at redhat.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)));
> >  
> >          Aml *crs = aml_resource_template();
> > 
> 
> -- 
> Shannon

On 29 July 2015 at 20:16, Michael S. Tsirkin <mst at redhat.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 at redhat.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

On Fri, Jul 31, 2015 at 01:37:44PM +0100, Peter Maydell
wrote:
> On 29 July 2015 at 20:16, Michael S. Tsirkin <mst at redhat.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 at redhat.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.
Yes, we have https://lkml.org/lkml/2015/7/28/216 in the RHELSA kernel.
Although, while that kernel is floating around already, it hasn't
really been released, particularly not for virt use cases. So we could
change it (although that change needs to be soon).
> 
> 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...
I'll remain abstained on this debate, but if the consensus is to
change it, then let me know, and I'll handle the changes on the
RHELSA side.

Thanks,
drew
> 
> [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
>