Re: [PATCH v3 RESEND] drivers/pci: Decouple DPC from AER service

[Darshit Shah]

Hi Bjorn,
Can you please pick this patch up in the PCI tree for the next version?
Anything I can do to help expedite the process?

* Darshit Shah <darnshah@xxxxxxxxx> [251211 16:43]:
> According to PCIe r7.0, sec. 6.2.11, "Implementation Note: Determination
> of DPC Control", it is recommended that the Operating System link the
> enablement of Downstream Port Containment (DPC) to the enablement of
> Advanced Error Reporting (AER).
> 
> However, AER is advertised only on Root Port (RP) or Root Complex Event
> Collector (RCEC) devices. On the other hand, DPC may be advertised on
> any PCIe device in the hierarchy. In fact, since the main usecase of DPC
> is for the switch upstream of an endpoint device to trigger a signal to
> the host-bridge, it is imperative that it be supported on non-RP,
> non-RCEC devices.
> 
> Previously portdrv has interpreted the spec to mean that the AER service
> must be available on the same device in order for DPC to be available.
> This is not what the implementation note meant to imply. If the firmware
> hands Linux control of AER via _OSC on the host bridge upstream of the
> device, then Linux should be allowed to assume control of DPC on the device.
> 
> The comment above this check alludes to this, by saying:
>   > With dpc-native, allow Linux to use DPC even if it doesn't have
>   > permission to use AER.
> 
> However, permission to use AER is negotiated at the host bridge, not
> per-device. So we should not link DPC to enabling AER at the device.
> Instead, DPC should be enabled if the OS has control of AER for the
> host bridge that is upstream of the device in question, or if dpc-native
> was set on the command line.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Darshit Shah <darnshah@xxxxxxxxx>
> Reviewed-by: Lukas Wunner <lukas@xxxxxxxxx>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> ---
> Changes from v2:
>   * + stable@xxxxxxxxxxxxxxx since moving to v6.2+ breaks DPC on our systems
>   * Minor stylistic changes to commit message
>   * NO functional changes
> 
>  drivers/pci/pcie/portdrv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c
> index 38a41ccf79b9..8db2fa140ae2 100644
> --- a/drivers/pci/pcie/portdrv.c
> +++ b/drivers/pci/pcie/portdrv.c
> @@ -264,7 +264,7 @@ static int get_port_device_capability(struct pci_dev *dev)
>  	 */
>  	if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DPC) &&
>  	    pci_aer_available() &&
> -	    (pcie_ports_dpc_native || (services & PCIE_PORT_SERVICE_AER)))
> +	    (host->native_aer || pcie_ports_dpc_native))
>  		services |= PCIE_PORT_SERVICE_DPC;
>  
>  	/* Enable bandwidth control if more than one speed is supported. */
> -- 
> 2.47.3
> 
> 
> 
> 
> Amazon Web Services Development Center Germany GmbH
> Tamara-Danz-Str. 13
> 10243 Berlin
> Geschaeftsfuehrung: Christof Hellmis, Andreas Stieger
> Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B
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> Ust-ID: DE 365 538 597



Amazon Web Services Development Center Germany GmbH
Tamara-Danz-Str. 13
10243 Berlin
Geschaeftsfuehrung: Christof Hellmis, Andreas Stieger
Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B
Sitz: Berlin
Ust-ID: DE 365 538 597