netdev - Re: [PATCH V3 1/6] vDPA/ifcvf: get_vendor_id returns a device specific vendor id

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Date:   Thu, 11 Mar 2021 14:13:20 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Zhu Lingshan <lingshan.zhu@...ux.intel.com>,
        Zhu Lingshan <lingshan.zhu@...el.com>, mst@...hat.com,
        lulu@...hat.com, leonro@...dia.com
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 1/6] vDPA/ifcvf: get_vendor_id returns a device
 specific vendor id


On 2021/3/11 12:21 下午, Zhu Lingshan wrote:
>
>
> On 3/11/2021 11:23 AM, Jason Wang wrote:
>>
>> On 2021/3/10 5:00 下午, Zhu Lingshan wrote:
>>> In this commit, ifcvf_get_vendor_id() will return
>>> a device specific vendor id of the probed pci device
>>> than a hard code.
>>>
>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
>>> ---
>>>   drivers/vdpa/ifcvf/ifcvf_main.c | 5 ++++-
>>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/vdpa/ifcvf/ifcvf_main.c 
>>> b/drivers/vdpa/ifcvf/ifcvf_main.c
>>> index fa1af301cf55..e501ee07de17 100644
>>> --- a/drivers/vdpa/ifcvf/ifcvf_main.c
>>> +++ b/drivers/vdpa/ifcvf/ifcvf_main.c
>>> @@ -324,7 +324,10 @@ static u32 ifcvf_vdpa_get_device_id(struct 
>>> vdpa_device *vdpa_dev)
>>>     static u32 ifcvf_vdpa_get_vendor_id(struct vdpa_device *vdpa_dev)
>>>   {
>>> -    return IFCVF_SUBSYS_VENDOR_ID;
>>> +    struct ifcvf_adapter *adapter = vdpa_to_adapter(vdpa_dev);
>>> +    struct pci_dev *pdev = adapter->pdev;
>>> +
>>> +    return pdev->subsystem_vendor;
>>>   }
>>
>>
>> While at this, I wonder if we can do something similar in 
>> get_device_id() if it could be simple deduced from some simple math 
>> from the pci device id?
>>
>> Thanks
> Hi Jason,
>
> IMHO, this implementation is just some memory read ops, I think other 
> implementations may not save many cpu cycles, an if cost at least 
> three cpu cycles.
>
> Thanks!


Well, I meant whehter you can deduce virtio device id from 
pdev->subsystem_device.

Thanks


>>
>>
>>>     static u32 ifcvf_vdpa_get_vq_align(struct vdpa_device *vdpa_dev)
>>
>