[PATCH] pci: Do not read INTx PIN and LINE registers for virtual functions

[PATCH] pci: Do not read INTx PIN and LINE registers for virtual functions

[KarimAllah Ahmed]

... since INTx is not supported by-spec for virtual functions.

Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-pci@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
---
 drivers/pci/probe.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 65099d0..61002fb 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1232,6 +1232,13 @@ static void pci_read_irq(struct pci_dev *dev)
 {
 	unsigned char irq;
 
+	/* Virtual functions do not have INTx support */
+	if (dev->is_virtfn) {
+		dev->pin = 0;
+		dev->irq = 0;
+		return;
+	}
+
 	pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &irq);
 	dev->pin = irq;
 	if (irq)
-- 
2.7.4

Re: [PATCH] pci: Do not read INTx PIN and LINE registers for virtual functions

[Alex Williamson]

On Wed, 17 Jan 2018 19:30:29 +0100
KarimAllah Ahmed <karahmed@amazon.de> wrote:

> ... since INTx is not supported by-spec for virtual functions.

But the spec also states that VFs must implement the interrupt pin
register as read-only zero, so either this is redundant or it's a
workaround for VFs that aren't quite compliant?  Thanks,

Alex

> 
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: linux-pci@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
> Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
> ---
>  drivers/pci/probe.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 65099d0..61002fb 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1232,6 +1232,13 @@ static void pci_read_irq(struct pci_dev *dev)
>  {
>  	unsigned char irq;
>  
> +	/* Virtual functions do not have INTx support */
> +	if (dev->is_virtfn) {
> +		dev->pin = 0;
> +		dev->irq = 0;
> +		return;
> +	}
> +
>  	pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &irq);
>  	dev->pin = irq;
>  	if (irq)

Re: [PATCH] pci: Do not read INTx PIN and LINE registers for virtual functions

[KarimAllah Ahmed]

On 01/17/2018 07:49 PM, Alex Williamson wrote:
> On Wed, 17 Jan 2018 19:30:29 +0100
> KarimAllah Ahmed <karahmed@amazon.de> wrote:
>
>> ... since INTx is not supported by-spec for virtual functions.
> But the spec also states that VFs must implement the interrupt pin
> register as read-only zero, so either this is redundant or it's a
> workaround for VFs that aren't quite compliant?  Thanks,

The end goal for me is just to NOT do the read across the PCI bus for no 
good reason. We have devices with thousands of virtual functions and 
this read is simply not useful in this case and can be optimized as I 
did. So from a functionality point of view probably the patch does not 
add any value as you mentioned, but it is really useful as a 
micro-optimization.

>
> Alex
>
>> Cc: Bjorn Helgaas <bhelgaas@google.com>
>> Cc: linux-pci@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
>> Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
>> ---
>>   drivers/pci/probe.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>> index 65099d0..61002fb 100644
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -1232,6 +1232,13 @@ static void pci_read_irq(struct pci_dev *dev)
>>   {
>>   	unsigned char irq;
>>   
>> +	/* Virtual functions do not have INTx support */
>> +	if (dev->is_virtfn) {
>> +		dev->pin = 0;
>> +		dev->irq = 0;
>> +		return;
>> +	}
>> +
>>   	pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &irq);
>>   	dev->pin = irq;
>>   	if (irq)
>

Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B

Re: [PATCH] pci: Do not read INTx PIN and LINE registers for virtual functions

[KarimAllah Ahmed]
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Re: [PATCH] pci: Do not read INTx PIN and LINE registers for virtual functions

[Alex Williamson]

On Wed, 17 Jan 2018 20:02:44 +0100
KarimAllah Ahmed <karahmed@amazon.com> wrote:

> On 01/17/2018 07:49 PM, Alex Williamson wrote:
> > On Wed, 17 Jan 2018 19:30:29 +0100
> > KarimAllah Ahmed <karahmed@amazon.de> wrote:
> >  
> >> ... since INTx is not supported by-spec for virtual functions.  
> > But the spec also states that VFs must implement the interrupt pin
> > register as read-only zero, so either this is redundant or it's a
> > workaround for VFs that aren't quite compliant?  Thanks,  
> 
> The end goal for me is just to NOT do the read across the PCI bus for no 
> good reason. We have devices with thousands of virtual functions and 
> this read is simply not useful in this case and can be optimized as I 
> did. So from a functionality point of view probably the patch does not 
> add any value as you mentioned, but it is really useful as a 
> micro-optimization.

Thanks for the clarification, it's helpful to understand the motivation
for a patch that otherwise seems unnecessary.

Alex

> >> Cc: Bjorn Helgaas <bhelgaas@google.com>
> >> Cc: linux-pci@vger.kernel.org
> >> Cc: linux-kernel@vger.kernel.org
> >> Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
> >> Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
> >> ---
> >>   drivers/pci/probe.c | 7 +++++++
> >>   1 file changed, 7 insertions(+)
> >>
> >> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> >> index 65099d0..61002fb 100644
> >> --- a/drivers/pci/probe.c
> >> +++ b/drivers/pci/probe.c
> >> @@ -1232,6 +1232,13 @@ static void pci_read_irq(struct pci_dev *dev)
> >>   {
> >>   	unsigned char irq;
> >>   
> >> +	/* Virtual functions do not have INTx support */
> >> +	if (dev->is_virtfn) {
> >> +		dev->pin = 0;
> >> +		dev->irq = 0;
> >> +		return;
> >> +	}
> >> +
> >>   	pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &irq);
> >>   	dev->pin = irq;
> >>   	if (irq)  
> >  
> 
> Amazon Development Center Germany GmbH
> Berlin - Dresden - Aachen
> main office: Krausenstr. 38, 10117 Berlin
> Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
> Ust-ID: DE289237879
> Eingetragen am Amtsgericht Charlottenburg HRB 149173 B

Re: [PATCH] pci: Do not read INTx PIN and LINE registers for virtual functions

[Bjorn Helgaas]

On Wed, Jan 17, 2018 at 07:30:29PM +0100, KarimAllah Ahmed wrote:
> ... since INTx is not supported by-spec for virtual functions.
> 
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: linux-pci@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
> Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>

Applied to pci/virtualization for v4.17, thanks!

I tweaked the changelog to include the motivation:

commit 16edf1c6345ab177ccf1e8b5ba3324ee01a50eb7
Author: KarimAllah Ahmed <karahmed@amazon.de>
Date:   Wed Jan 17 19:30:29 2018 +0100

    PCI/IOV: Skip INTx config reads for VFs
    
    Per PCIe r4.0, sec 9.2.1.4, VFs can not implement INTX, and their Interrupt
    Line and Interrupt Pin registers must be RO Zero.  Some devices have
    thousands of VFs, so skip reading the registers as an optimization.
    
    Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
    Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
    [bhelgaas: changelog, comment]
    Signed-off-by: Bjorn Helgaas <helgaas@kernel.org>

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 489660d0d384..a1cddca37793 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1230,6 +1230,13 @@ static void pci_read_irq(struct pci_dev *dev)
 {
 	unsigned char irq;
 
+	/* VFs are not allowed to use INTx, so skip the config reads */
+	if (dev->is_virtfn) {
+		dev->pin = 0;
+		dev->irq = 0;
+		return;
+	}
+
 	pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &irq);
 	dev->pin = irq;
 	if (irq)