Re: [Minios-devel] [UNIKRAFT PATCH] plat/virtio: Update off-by-one device id

[Sharan Santhanam <sharan.santhanam@xxxxxxxxx>]

Hey Cristian Banu,

The original idea of subtracting the 0x0FFF is flawed as there is 
mismatch in following the device(s) [1], [2].
* network device (legacy)
* block device (legacy)
* SCSI host bus adapter device
* entropy generator device

Instead of this solution what we could do is:

@@ -364,8 +363,7 @@ static int virtio_pci_legacy_add_dev(struct 
pci_device *pci_dev,
                   pci_dev->id.device_id);

        /* Mapping the virtio device identifier */
-       virtio_device_id_add(&vpci_dev->vdev, pci_dev->id.device_id,
-                            VIRTIO_PCI_LEGACY_DEVICEID_START);
+       vpci_dev->vdev.id.virtio_device_id = 
pci_dev->id.subsystem_device_id;
In qemu they set this value as per patch series [3]


[1] https://lists.oasis-open.org/archives/virtio/201406/msg00007.html
[2] 
https://virtio-dev.oasis-open.narkive.com/ZJpUKtPi/patch-pci-switch-from-subsystem-id-to-device-id
[3] https://patchwork.kernel.org/patch/10038753/

Thanks & Regards
Sharan

On 12/05/2018 04:15 PM, Cristian Banu wrote:
> The virtio_device_id is computed as the difference between pci_dev_id
> and VIRTIO_PCI_LEGACY_DEVICEID_START. Considering the values for device
> ids given in virtio_ids.h, the previous value of 0x0FFF would have
> created an off-by-one error in virtio_device_id.
>
> For example, a 9P device has pci_dev_id = 0x1009, thus virtio_device_id
> would've been 0xA instead of 0x9, as required by virtio_ids.h.
>
> Signed-off-by: Cristian Banu <cristb@xxxxxxxxx>
> ---
>   plat/drivers/virtio/virtio_pci.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/plat/drivers/virtio/virtio_pci.c b/plat/drivers/virtio/virtio_pci.c
> index 8503b534d054..44b1fc8e7f12 100644
> --- a/plat/drivers/virtio/virtio_pci.c
> +++ b/plat/drivers/virtio/virtio_pci.c
> @@ -46,7 +46,7 @@
>   #include <virtio/virtio_pci.h>
>   
>   #define VENDOR_QUMRANET_VIRTIO           (0x1AF4)
> -#define VIRTIO_PCI_LEGACY_DEVICEID_START (0x0FFF)
> +#define VIRTIO_PCI_LEGACY_DEVICEID_START (0x1000)
>   #define VIRTIO_PCI_MODERN_DEVICEID_START (0x1040)
>   
>   static struct uk_alloc *a;
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