[v2] bus: mhi: host: Enable SRIOV support in MHI driver

[PATCH v2 2/5] bus: mhi: host: pci_generic: Read SUBSYSTEM_VENDOR_ID for VF's to check status

Posted by Vivek.Pernamitta@quicinc.com 2 months, 4 weeks ago

From: Vivek Pernamitta <quic_vpernami@quicinc.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@quicinc.com>
Reviewed-by: Krishna Chaitanya Chundru <krishna.chundru@oss.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);
 
 	if (vendor == (u16) ~0 || vendor == 0)
 		return false;

-- 
2.34.1

Re: [PATCH v2 2/5] bus: mhi: host: pci_generic: Read SUBSYSTEM_VENDOR_ID for VF's to check status

Posted by Manivannan Sadhasivam 2 months ago

On Thu, Jul 10, 2025 at 02:28:33PM GMT, Vivek.Pernamitta@quicinc.com wrote:
> From: Vivek Pernamitta <quic_vpernami@quicinc.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@quicinc.com>
> Reviewed-by: Krishna Chaitanya Chundru <krishna.chundru@oss.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.

- Mani

-- 
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Re: [PATCH v2 2/5] bus: mhi: host: pci_generic: Read SUBSYSTEM_VENDOR_ID for VF's to check status

Posted by Krishna Chaitanya Chundru 2 months ago


On 8/6/2025 10:29 PM, Manivannan Sadhasivam wrote:
> On Thu, Jul 10, 2025 at 02:28:33PM GMT, Vivek.Pernamitta@quicinc.com wrote:
>> From: Vivek Pernamitta <quic_vpernami@quicinc.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@quicinc.com>
>> Reviewed-by: Krishna Chaitanya Chundru <krishna.chundru@oss.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.

- Krishna Chaitanya.
> - Mani
>

Re: [PATCH v2 2/5] bus: mhi: host: pci_generic: Read SUBSYSTEM_VENDOR_ID for VF's to check status

Posted by Manivannan Sadhasivam 2 months ago

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@quicinc.com wrote:
> > > From: Vivek Pernamitta <quic_vpernami@quicinc.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@quicinc.com>
> > > Reviewed-by: Krishna Chaitanya Chundru <krishna.chundru@oss.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.

- Mani

-- 
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Re: [PATCH v2 2/5] bus: mhi: host: pci_generic: Read SUBSYSTEM_VENDOR_ID for VF's to check status

Posted by Krishna Chaitanya Chundru 2 months ago


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@quicinc.com wrote:
>>>> From: Vivek Pernamitta <quic_vpernami@quicinc.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@quicinc.com>
>>>> Reviewed-by: Krishna Chaitanya Chundru <krishna.chundru@oss.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
>

Re: [PATCH v2 2/5] bus: mhi: host: pci_generic: Read SUBSYSTEM_VENDOR_ID for VF's to check status

Posted by Manivannan Sadhasivam 2 months ago

On Thu, Aug 07, 2025 at 01:45:42PM GMT, Krishna Chaitanya Chundru wrote:
> 
> 
> 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@quicinc.com wrote:
> > > > > From: Vivek Pernamitta <quic_vpernami@quicinc.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@quicinc.com>
> > > > > Reviewed-by: Krishna Chaitanya Chundru <krishna.chundru@oss.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.
> 

Oh well yes. Otherwise, we will end up with 'num_vfs' number of health monitor
threads eating up the CPU time for no good reason.

- Mani

-- 
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