linux-kernel - Re: [PATCH 2/2] PCI: vmd: Let OS control ASPM for devices under VMD domain

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Message-ID: <20240802000414.GA127813@bhelgaas>
Date: Thu, 1 Aug 2024 19:04:14 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc: bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, nirmal.patel@...ux.intel.com,
	jonathan.derrick@...ux.dev, ilpo.jarvinen@...ux.intel.com,
	david.e.box@...ux.intel.com
Subject: Re: [PATCH 2/2] PCI: vmd: Let OS control ASPM for devices under VMD
 domain

On Thu, May 30, 2024 at 04:52:27PM +0800, Kai-Heng Feng wrote:
> Intel SoC cannot reach lower power states when mapped VMD PCIe bridges
> and NVMe devices don't have ASPM configured.
> 
> So set aspm_os_control attribute to let OS really enable ASPM for those
> devices.
> 
> Fixes: f492edb40b54 ("PCI: vmd: Add quirk to configure PCIe ASPM and LTR")

I assume f492edb40b54 was tested and worked at the time.  Is the
implication that newer Intel SoCs have added more requirements for
getting to low power states, since __pci_enable_link_state() would
have warned and done nothing even then?

Or maybe this is a new system that sets ACPI_FADT_NO_ASPM, and
f492edb40b54 was tested on systems that did *not* set
ACPI_FADT_NO_ASPM?

> Link: https://lore.kernel.org/linux-pm/218aa81f-9c6-5929-578d-8dc15f83dd48@panix.com/
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>  drivers/pci/controller/vmd.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index 87b7856f375a..1dbc525c473f 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -751,6 +751,8 @@ static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
>  	if (!(features & VMD_FEAT_BIOS_PM_QUIRK))
>  		return 0;
>  
> +	pdev->aspm_os_control = 1;
> +
>  	pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);
>  
>  	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_LTR);
> -- 
> 2.43.0
>