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Subject: Re: [PATCH V3 1/6] vDPA/ifcvf: get_vendor_id returns a device
 specific vendor id
To:     Jason Wang <jasowang@redhat.com>,
        Zhu Lingshan <lingshan.zhu@intel.com>, mst@redhat.com,
        lulu@redhat.com, leonro@nvidia.com
Cc:     virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210310090052.4762-1-lingshan.zhu@intel.com>
 <20210310090052.4762-2-lingshan.zhu@intel.com>
 <ff5fc8f9-f886-bd2a-60cc-771c628c6c4b@redhat.com>
From:   Zhu Lingshan <lingshan.zhu@linux.intel.com>
Message-ID: <5f2d915f-e1b0-c9eb-9fc8-4b64f5d8cd0f@linux.intel.com>
Date:   Thu, 11 Mar 2021 12:21:45 +0800
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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@intel.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!
>
>
>>     static u32 ifcvf_vdpa_get_vq_align(struct vdpa_device *vdpa_dev)
>