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 15:34:34 +0800
From:   "Zhu, Lingshan" <lingshan.zhu@...el.com>
To:     Jason Wang <jasowang@...hat.com>,
        Zhu Lingshan <lingshan.zhu@...ux.intel.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 3/11/2021 2:13 PM, Jason Wang wrote:
>
> 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
Oh, sure, I get you
>
>
>>>
>>>
>>>>     static u32 ifcvf_vdpa_get_vq_align(struct vdpa_device *vdpa_dev)
>>>
>>
>