Re: [PATCH v2] PCI/portdrv: Do not require an interrupt for all AER capable ports

[Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@linux.intel.com>]

On 12/9/22 9:07 AM, Bjorn Helgaas wrote:
> On Wed, Dec 07, 2022 at 10:41:05AM +0200, Mika Westerberg wrote:
>> Only Root Ports and Event Collectors use MSI for AER. PCIe Switch ports
>> or endpoints on the other hand only send messages (that get collected by
>> the former). For this reason do not require PCIe switch ports and
>> endpoints to use interrupt if they support AER.
>>
>> This allows portdrv to attach PCIe switch ports of Intel DG1 and DG2
>> discrete graphics cards. These do not declare MSI or legacy interrupts.
>>
>> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> 
> Thanks for the additional info!  This seems like something we should
> definitely do.
> 
> I'm wondering whether we should check for this in
> get_port_device_capability().  It already has similar checks for
> device type for other services.  This would skip pci_set_master() for
> these non-RP, non-RCEC devices, which is probably harmless, since I
> assume we only need that to make sure MSI works.

Currently, we only have high level (cap or enable/disable) checks in 
get_port_device_capability(). Why bring in more AER specific checks
there and make it complicated? Is there any benefit in doing this?

> 
> It would also prevent allocation of the AER service for non-RP,
> non-RCEC devices.  That's also probably harmless, since aer_probe()
> ignores those devices anyway.
> 
> What do you think of something like this?  (This is based on my
> pci/portdrv branch which squashed everything into portdrv.c:
> https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/log/?h=pci/portdrv)
> 
> 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

If you want to do it, will you remove the relevant check in AER driver
probe?


-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer