linux-kernel - Re: [PATCH v2 2/5] bus: mhi: host: pci_generic: Read SUBSYSTEM_VENDOR

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Message-ID: <7118392a-2a19-44a4-97c0-d5e8a3190c08@oss.qualcomm.com>
Date: Thu, 7 Aug 2025 13:45:42 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: Vivek.Pernamitta@...cinc.com, mhi@...ts.linux.dev,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vivek Pernamitta <quic_vpernami@...cinc.com>
Subject: Re: [PATCH v2 2/5] bus: mhi: host: pci_generic: Read
 SUBSYSTEM_VENDOR_ID for VF's to check status



On 8/7/2025 1:43 PM, Manivannan Sadhasivam wrote:
> On Thu, Aug 07, 2025 at 12:39:26PM GMT, Krishna Chaitanya Chundru wrote:
>>
>>
>> On 8/6/2025 10:29 PM, Manivannan Sadhasivam wrote:
>>> On Thu, Jul 10, 2025 at 02:28:33PM GMT, Vivek.Pernamitta@...cinc.com wrote:
>>>> From: Vivek Pernamitta <quic_vpernami@...cinc.com>
>>>>
>>>> In SRIOV enabled devices, the VF DEVICE/VENDOR ID register returns FFFFh
>>>> when read (PCIe SRIOV spec-3.4.1.1). Therefore, read the PCIe
>>>> SUBSYSTEM_VENDOR_ID to check if the device is active.
>>>>
>>>> Signed-off-by: Vivek Pernamitta <quic_vpernami@...cinc.com>
>>>> Reviewed-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
>>>> ---
>>>>    drivers/bus/mhi/host/pci_generic.c | 6 ++++--
>>>>    1 file changed, 4 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/bus/mhi/host/pci_generic.c b/drivers/bus/mhi/host/pci_generic.c
>>>> index 7d0ac1c34ddf95ace2a85e5f08884f51604d9b0f..4bafe93b56c54e2b091786e7fcd68a36c8247b8e 100644
>>>> --- a/drivers/bus/mhi/host/pci_generic.c
>>>> +++ b/drivers/bus/mhi/host/pci_generic.c
>>>> @@ -1025,8 +1025,10 @@ static bool mhi_pci_is_alive(struct mhi_controller *mhi_cntrl)
>>>>    	struct pci_dev *pdev = to_pci_dev(mhi_cntrl->cntrl_dev);
>>>>    	u16 vendor = 0;
>>>> -	if (pci_read_config_word(pdev, PCI_VENDOR_ID, &vendor))
>>>> -		return false;
>>>> +	if (pdev->is_virtfn)
>>>> +		pci_read_config_word(pdev, PCI_SUBSYSTEM_VENDOR_ID, &vendor);
>>>> +	else
>>>> +		pci_read_config_word(pdev, PCI_VENDOR_ID, &vendor);
>>>
>>> You should not read the sub Vendor ID for VF. PCIe spec suggests reading the PF
>>> Vendor ID for VF. So you should just use pci_physfn() API as below:
>>>
>>> 	pci_read_config_word(pci_physfn(pdev), PCI_VENDOR_ID, &vendor);
>>>
>>> This will work for both PF and VF.
>>>
>> This will defeat the purpose of having health check monitor for VF,
>> as we are always reading PF vendor ID and will not know VF status at all.
> 
> Do we really have a usecase to perform health check for VFs? Health check is
> supposed to happen for devices that can fail abruptly.
> 
yeah as VF is not a physical link we can disable health check monitor
for VF's in the probe itself.

- Krishna Chaitanya.
> - Mani
>