Re: [Qemu-devel] [PATCH v2] arm: change vendor ID for virtio-mmio

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Jul 30, 2015 at 05:21:51PM +0800, Shannon Zhao wrote:
> 
> 
> On 2015/7/30 16:04, Michael S. Tsirkin wrote:
> > 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.
> > 
> 
> I think kernel driver supports multiple IDs. If they don't want to
> "QEMUXXXX" as ACPI ID, it's free to add a new one like below.
> 
> +static const struct acpi_device_id virtio_mmio_acpi_match[] = {
> +       { "QEMU0005", },
> +       { "1AF4103F", },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(acpi, virtio_mmio_acpi_match);

Yes but that won't work with existing disto kernels.

> > 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@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
> > 
> > .
> > 
> 
> -- 
> Shannon