Re: [PATCH] PCI/ASPM: Enable ASPM on external PCIe devices

[Sathyanarayanan Kuppuswamy]

On 6/15/23 12:04 AM, Kai-Heng Feng wrote:
> When a PCIe device is hotplugged to a Thunderbolt port, ASPM is not
> enabled for that device. However, when the device is plugged preboot,
> ASPM is enabled by default.
> 
> The disparity happens because BIOS doesn't have the ability to program
> ASPM on hotplugged devices.
> 
> So enable ASPM by default for external connected PCIe devices so ASPM
> settings are consitent between preboot and hotplugged.

Why it has to be consistent? Can you add info about what it solves?

> 
> On HP Thunderbolt Dock G4, enable ASPM can also fix BadDLLP error:
> pcieport 0000:00:1d.0: AER: Corrected error received: 0000:07:04.0
> pcieport 0000:07:04.0: PCIe Bus Error: severity=Corrected, type=Data Link Layer, (Receiver ID)
> pcieport 0000:07:04.0:   device [8086:0b26] error status/mask=00000080/00002000
> pcieport 0000:07:04.0:    [ 7] BadDLLP
> 
> The root cause is still unclear, but quite likely because the I225 on
> the dock supports PTM, where ASPM timing is precalculated for the PTM.
> 
> Cc: Mario Limonciello <mario.limonciello@xxxxxxx>
> Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217557
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
> ---
>  drivers/pci/pcie/aspm.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 66d7514ca111..613b0754c9bb 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -119,7 +119,9 @@ static int policy_to_aspm_state(struct pcie_link_state *link)
>  		/* Enable Everything */
>  		return ASPM_STATE_ALL;
>  	case POLICY_DEFAULT:
> -		return link->aspm_default;
> +		return dev_is_removable(&link->downstream->dev) ?
> +			link->aspm_capable :
> +			link->aspm_default;
>  	}
>  	return 0;
>  }

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer