linux-kernel - Re: [PATCH] PCI/ASPM: Allow drivers to disable ASPM even without OS ASPM control

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Date:   Fri, 10 Feb 2017 16:47:28 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     linux-pci@...r.kernel.org,
        Mathias Koehrer <mathias.koehrer@...s.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        Sebastian Andrzej Siewior <sebastian.siewior@...utronix.de>,
        Julia Cartwright <julia@...com>,
        Joe Lawrence <joe.lawrence@...atus.com>,
        linux-kernel@...r.kernel.org, Matthew Garrett <mjg59@...eos.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Colin Ian King <colin.king@...onical.com>,
        Myron Stowe <myron.stowe@...hat.com>
Subject: Re: [PATCH] PCI/ASPM: Allow drivers to disable ASPM even without OS
 ASPM control

On Tue, Jan 24, 2017 at 02:23:01PM -0600, Bjorn Helgaas wrote:
> The ACPI FADT has a "PCIe ASPM Controls" bit (ACPI 5.0, sec 5.2.9.3), which
> means "If set, indicates to OSPM that it must not enable ASPM control on
> this platform."  We have historically interpreted that to mean that the OS
> should not touch ASPM configuration at all: we leave it as the firmware
> configured it.
> 
> However, a driver may know that its device has issues with ASPM and should
> not have it enabled.  The platform firmware, which cannot be expected to
> know this, may have enabled ASPM.  The driver should be able to use
> pci_disable_link_state() to disable ASPM for its device, even if the
> firmware set the ACPI_FADT_NO_ASPM bit.
> 
> Remove the check that prevents pci_disable_link_state() from disabling ASPM
> for a device.
> 
> In cases where we previously emitted a message like this and did nothing:
> 
>   e1000e 0000:03:00.0: can't disable ASPM; OS doesn't have ASPM control
> 
> we'll instead actually disable ASPM on the device.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=189951
> Reported-by: Mathias Koehrer <mathias.koehrer@...s.com>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> CC: Matthew Garrett <mjg59@...eos.com>
> CC: stable@...r.kernel.org

I think this is the right thing to do, but I haven't applied this yet
because I don't think it's quite enough in its current form.

Even if I applied this, it would only allow a driver to disable ASPM
if CONFIG_PCIEASPM is enabled.  Without CONFIG_PCIEASPM, we don't
compile aspm.c and pci_disable_link_state() is a stub that does
nothing.

I think we need to make pci_disable_link_state() work even when
CONFIG_PCIEASPM is not enabled.  If we did that, we could clean up
callers like __e1000e_disable_aspm(), which contains code to disable
ASPM manually if pci_disable_link_state() doesn't work.

There are other drivers that try to disable ASPM because of device
errata, and currently that only works when CONFIG_PCIEASPM is enabled.
If we add a pci_disable_link_state() that works when CONFIG_PCIEASPM
is not enabled, it should make those drivers work better.

> ---
>  drivers/pci/pcie/aspm.c |   16 ++++------------
>  1 file changed, 4 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 17ac1dce3286..9253ae48d777 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -736,18 +736,10 @@ static void __pci_disable_link_state(struct pci_dev *pdev, int state, bool sem)
>  	if (!parent || !parent->link_state)
>  		return;
>  
> -	/*
> -	 * A driver requested that ASPM be disabled on this device, but
> -	 * if we don't have permission to manage ASPM (e.g., on ACPI
> -	 * systems we have to observe the FADT ACPI_FADT_NO_ASPM bit and
> -	 * the _OSC method), we can't honor that request.  Windows has
> -	 * a similar mechanism using "PciASPMOptOut", which is also
> -	 * ignored in this situation.
> -	 */
> -	if (aspm_disabled) {
> -		dev_warn(&pdev->dev, "can't disable ASPM; OS doesn't have ASPM control\n");
> -		return;
> -	}
> +	dev_info(&pdev->dev, "disabling %sASPM%s%s\n",
> +		 (state & PCIE_LINK_STATE_CLKPM) ? "Clock PM " : "",
> +		 (state & PCIE_LINK_STATE_L0S) ? " L0s" : "",
> +		 (state & PCIE_LINK_STATE_L1) ? " L1" : "");
>  
>  	if (sem)
>  		down_read(&pci_bus_sem);
>