netdev - Re: [PATCH v3 virtio 1/8] virtio: allow caller to override device id and DMA mask

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Date:   Fri, 24 Mar 2023 17:26:28 -0700
From:   Shannon Nelson <shannon.nelson@....com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, virtualization@...ts.linux-foundation.org,
        brett.creeley@....com, davem@...emloft.net, netdev@...r.kernel.org,
        kuba@...nel.org, drivers@...sando.io
Subject: Re: [PATCH v3 virtio 1/8] virtio: allow caller to override device id
 and DMA mask

On 3/22/23 9:05 PM, Jason Wang wrote:
> On Thu, Mar 23, 2023 at 3:11 AM Shannon Nelson <shannon.nelson@....com> wrote:
>>
>> To allow a bit of flexibility with various virtio based devices, allow
>> the caller to specify a different device id and DMA mask.  This adds
>> fields to struct XXX to specify an override device id check and a DMA mask.
>>
>> Signed-off-by: Shannon Nelson <shannon.nelson@....com>
>> ---
>>   drivers/virtio/virtio_pci_modern_dev.c | 36 +++++++++++++++++---------
>>   include/linux/virtio_pci_modern.h      |  6 +++++
>>   2 files changed, 30 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_pci_modern_dev.c b/drivers/virtio/virtio_pci_modern_dev.c
>> index 869cb46bef96..6ad1bb9ae8fa 100644
>> --- a/drivers/virtio/virtio_pci_modern_dev.c
>> +++ b/drivers/virtio/virtio_pci_modern_dev.c
>> @@ -221,18 +221,25 @@ int vp_modern_probe(struct virtio_pci_modern_device *mdev)
>>
>>          check_offsets();
>>
>> -       /* We only own devices >= 0x1000 and <= 0x107f: leave the rest. */
>> -       if (pci_dev->device < 0x1000 || pci_dev->device > 0x107f)
>> -               return -ENODEV;
>> -
>> -       if (pci_dev->device < 0x1040) {
>> -               /* Transitional devices: use the PCI subsystem device id as
>> -                * virtio device id, same as legacy driver always did.
>> -                */
>> -               mdev->id.device = pci_dev->subsystem_device;
>> +       if (mdev->device_id_check_override) {
>> +               err = mdev->device_id_check_override(pci_dev);
>> +               if (err)
>> +                       return err;
>> +               mdev->id.device = pci_dev->device;
> 
> While at this, would it be better to let the device_id_check_override
> to return the mdev->id.device ?

Good idea - I'll add that.
sln


> 
> Others look good.
> 
> Thanks
> 
>>          } else {
>> -               /* Modern devices: simply use PCI device id, but start from 0x1040. */
>> -               mdev->id.device = pci_dev->device - 0x1040;
>> +               /* We only own devices >= 0x1000 and <= 0x107f: leave the rest. */
>> +               if (pci_dev->device < 0x1000 || pci_dev->device > 0x107f)
>> +                       return -ENODEV;
>> +
>> +               if (pci_dev->device < 0x1040) {
>> +                       /* Transitional devices: use the PCI subsystem device id as
>> +                        * virtio device id, same as legacy driver always did.
>> +                        */
>> +                       mdev->id.device = pci_dev->subsystem_device;
>> +               } else {
>> +                       /* Modern devices: simply use PCI device id, but start from 0x1040. */
>> +                       mdev->id.device = pci_dev->device - 0x1040;
>> +               }
>>          }
>>          mdev->id.vendor = pci_dev->subsystem_vendor;
>>
>> @@ -260,7 +267,12 @@ int vp_modern_probe(struct virtio_pci_modern_device *mdev)
>>                  return -EINVAL;
>>          }
>>
>> -       err = dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(64));
>> +       if (mdev->dma_mask_override)
>> +               err = dma_set_mask_and_coherent(&pci_dev->dev,
>> +                                               mdev->dma_mask_override);
>> +       else
>> +               err = dma_set_mask_and_coherent(&pci_dev->dev,
>> +                                               DMA_BIT_MASK(64));
>>          if (err)
>>                  err = dma_set_mask_and_coherent(&pci_dev->dev,
>>                                                  DMA_BIT_MASK(32));
>> diff --git a/include/linux/virtio_pci_modern.h b/include/linux/virtio_pci_modern.h
>> index c4eeb79b0139..84765bbd8dc5 100644
>> --- a/include/linux/virtio_pci_modern.h
>> +++ b/include/linux/virtio_pci_modern.h
>> @@ -38,6 +38,12 @@ struct virtio_pci_modern_device {
>>          int modern_bars;
>>
>>          struct virtio_device_id id;
>> +
>> +       /* alt. check for vendor virtio device, return 0 or -ERRNO */
>> +       int (*device_id_check_override)(struct pci_dev *pdev);
>> +
>> +       /* alt. mask for devices with limited DMA space */
>> +       u64 dma_mask_override;
>>   };
>>
>>   /*
>> --
>> 2.17.1
>>
>