PCI/portdrv: Do not setup up IRQs if there are no users

From: Jan Kiszka <jan.kiszka@siemens.com>

Avoid registering service IRQs if there is no service that offers them
or no driver to register a handler against them. This saves IRQ vectors
when they are limited (e.g. on x86) and also avoids that spurious events
could hit a missing handler. Such spurious events need to be generated
by the Jailhouse hypervisor for active MSI vectors when enabling or
disabling itself.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 drivers/pci/pcie/portdrv_core.c | 40 ++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 13 deletions(-)

On Fri, Aug 20, 2021 at 03:52:18PM +0200, Jan Kiszka wrote:
> --- a/drivers/pci/pcie/portdrv_core.c
> +++ b/drivers/pci/pcie/portdrv_core.c
> @@ -312,7 +312,7 @@ static int pcie_device_init(struct pci_dev *pdev, int service, int irq)
>   */
>  int pcie_port_device_register(struct pci_dev *dev)
>  {
> -	int status, capabilities, i, nr_service;
> +	int status, capabilities, irq_services, i, nr_service;
>  	int irqs[PCIE_PORT_DEVICE_MAXSERVICES];
>  
>  	/* Enable PCI Express port device */
> @@ -326,18 +326,32 @@ int pcie_port_device_register(struct pci_dev *dev)
>  		return 0;
>  
>  	pci_set_master(dev);
> -	/*
> -	 * Initialize service irqs. Don't use service devices that
> -	 * require interrupts if there is no way to generate them.
> -	 * However, some drivers may have a polling mode (e.g. pciehp_poll_mode)
> -	 * that can be used in the absence of irqs.  Allow them to determine
> -	 * if that is to be used.
> -	 */
> -	status = pcie_init_service_irqs(dev, irqs, capabilities);
> -	if (status) {
> -		capabilities &= PCIE_PORT_SERVICE_HP;
> -		if (!capabilities)
> -			goto error_disable;
> +
> +	irq_services = 0;
> +	if (IS_ENABLED(CONFIG_PCIE_PME))
> +		irq_services |= PCIE_PORT_SERVICE_PME;
> +	if (IS_ENABLED(CONFIG_PCIEAER))
> +		irq_services |= PCIE_PORT_SERVICE_AER;
> +	if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE))
> +		irq_services |= PCIE_PORT_SERVICE_HP;
> +	if (IS_ENABLED(CONFIG_PCIE_DPC))
> +		irq_services |= PCIE_PORT_SERVICE_DPC;
> +	irq_services &= capabilities;

get_port_device_capability() would seem like a more natural place
to put these checks.

Note that your check for CONFIG_PCIEAER is superfluous due to
the "#ifdef CONFIG_PCIEAER" in get_port_device_capability().

Thanks,

Lukas

On 20.08.21 16:45, Lukas Wunner wrote:
> On Fri, Aug 20, 2021 at 03:52:18PM +0200, Jan Kiszka wrote:
>> --- a/drivers/pci/pcie/portdrv_core.c
>> +++ b/drivers/pci/pcie/portdrv_core.c
>> @@ -312,7 +312,7 @@ static int pcie_device_init(struct pci_dev *pdev, int service, int irq)
>>   */
>>  int pcie_port_device_register(struct pci_dev *dev)
>>  {
>> -	int status, capabilities, i, nr_service;
>> +	int status, capabilities, irq_services, i, nr_service;
>>  	int irqs[PCIE_PORT_DEVICE_MAXSERVICES];
>>  
>>  	/* Enable PCI Express port device */
>> @@ -326,18 +326,32 @@ int pcie_port_device_register(struct pci_dev *dev)
>>  		return 0;
>>  
>>  	pci_set_master(dev);
>> -	/*
>> -	 * Initialize service irqs. Don't use service devices that
>> -	 * require interrupts if there is no way to generate them.
>> -	 * However, some drivers may have a polling mode (e.g. pciehp_poll_mode)
>> -	 * that can be used in the absence of irqs.  Allow them to determine
>> -	 * if that is to be used.
>> -	 */
>> -	status = pcie_init_service_irqs(dev, irqs, capabilities);
>> -	if (status) {
>> -		capabilities &= PCIE_PORT_SERVICE_HP;
>> -		if (!capabilities)
>> -			goto error_disable;
>> +
>> +	irq_services = 0;
>> +	if (IS_ENABLED(CONFIG_PCIE_PME))
>> +		irq_services |= PCIE_PORT_SERVICE_PME;
>> +	if (IS_ENABLED(CONFIG_PCIEAER))
>> +		irq_services |= PCIE_PORT_SERVICE_AER;
>> +	if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE))
>> +		irq_services |= PCIE_PORT_SERVICE_HP;
>> +	if (IS_ENABLED(CONFIG_PCIE_DPC))
>> +		irq_services |= PCIE_PORT_SERVICE_DPC;
>> +	irq_services &= capabilities;
> 
> get_port_device_capability() would seem like a more natural place
> to put these checks.
> 
> Note that your check for CONFIG_PCIEAER is superfluous due to
> the "#ifdef CONFIG_PCIEAER" in get_port_device_capability().
> 

Not all service drivers need IRQs. That's why the test is separate. See
also the comment I shuffled around.

Jan