Re: [PATCH v3] PCI/portdrv: Allow AER service only for Root Ports & RCECs

["Gupta, Anshuman" <anshuman.gupta@intel.com>]

On 12/10/2022 5:59 AM, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@google.com>
> 
> Previously portdrv allowed the AER service for any device with an AER
> capability (assuming Linux had control of AER) even though the AER service
> driver only attaches to Root Port and RCECs.
> 
> Because get_port_device_capability() included AER for non-RP, non-RCEC
> devices, we tried to initialize the AER IRQ even though these devices
> don't generate AER interrupts.
> 
> Intel DG1 and DG2 discrete graphics cards contain a switch leading to a
> GPU.  The switch supports AER but not MSI, so initializing an AER IRQ
> failed, and portdrv failed to claim the switch port at all.  The GPU itself
> could be suspended, but the switch could not be put in a low-power state
> because it had no driver.
Tested with Intel DG2 Card, virtual switch ports bind with pcieport 
driver and enters to lower power state.
Tested-by: Anshuman Gupta <anshuman.gupta@intel.com>

> 
> Don't allow the AER service on non-Root Port, non-Root Complex Event
> Collector devices.  This means we won't enable Bus Mastering if the device
> doesn't require MSI, the AER service will not appear in sysfs, and the AER
> service driver will not bind to the device.
> 
> Link: https://lore.kernel.org/r/20221207084105.84947-1-mika.westerberg@linux.intel.com
> Based-on-patch-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
> 
> This is a v3 based on Mika's patch at
> https://lore.kernel.org/r/20221207084105.84947-1-mika.westerberg@linux.intel.com
> 
> I wouldn't normally kibbitz like this, but I'm hoping to squeeze this into
> the v6.2 merge window.
> 
> Changes from v2:
> 
>    * Test the device type in get_port_device_capability() instead of
>      pcie_init_service_irqs().  The benefits are to keep the device type
>      checking together (this is similar to the PME test), avoid enabling Bus
>      Mastering unnecessarily, avoid exposing the portdrv AER service in
>      sysfs, and preventing the AER service driver from binding to devices it
>      doesn't need to.
> 
>   drivers/pci/pcie/portdrv.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c
> index a6c4225505d5..8b16e96ec15c 100644
> --- a/drivers/pci/pcie/portdrv.c
> +++ b/drivers/pci/pcie/portdrv.c
> @@ -232,7 +232,9 @@ static int get_port_device_capability(struct pci_dev *dev)
>   	}
>   
>   #ifdef CONFIG_PCIEAER
> -	if (dev->aer_cap && pci_aer_available() &&
> +	if ((pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
> +             pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC) &&
> +	    dev->aer_cap && pci_aer_available() &&
>   	    (pcie_ports_native || host->native_aer))
>   		services |= PCIE_PORT_SERVICE_AER;
>   #endif