Re: [PATCH v2 1/2] PCI/ACPI: Move _OSC test for native services to top

[Bjorn Helgaas <helgaas@kernel.org>]

Hi Aaron,

On Thu, Oct 25, 2018 at 11:01:31AM -0500, Aaron Sierra wrote:
> Move the simple test for when PCIe native services are disabled
> closer to the top, prior to where things get more complicated.
> 
> Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
> ---
>  drivers/acpi/pci_root.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index 707aafc..eb9f14e 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -441,6 +441,12 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
>  		return;
>  	}
>  
> +	if (pcie_ports_disabled) {
> +		dev_info(&device->dev,
> +			 "PCIe port services disabled; not requesting _OSC control\n");
> +		return;
> +	}

Today we always set "*no_aspm = 1" if _OSC fails, which means we later
call pcie_no_aspm().

After this patch, when pcie_ports_disabled is "true", we don't even try to
evaluate _OSC, and we will never set *no_aspm, so we will never call
pcie_no_aspm() when pcie_ports_disabled is "true", which happens in these
cases:

  1) CONFIG_PCIEPORTBUS is unset, or
  2) CONFIG_PCIEPORTBUS=y and we booted with "pcie_ports=compat"

Case 1) isn't a problem because pcie_no_aspm() is only implemented when
CONFIG_PCIEASPM=y, and CONFIG_PCIEASPM depends on CONFIG_PCIEPORTBUS, so in
this case today we only call the empty stub pcie_no_aspm() function.

But case 2) is a behavior change that seems unintended.

Even though CONFIG_PCIEASPM depends on CONFIG_PCIEPORTBUS, ASPM doesn't
actually *use* anything provided by PCIEPORTBUS, so I think the ASPM code
is still active and useful even when we boot with "pcie_ports=compat".

Whether CONFIG_PCIEASPM should depend on CONFIG_PCIEPORTBUS is another
question.  I tend to think maybe it should not, but that's an orthogonal
question.

>  	/*
>  	 * All supported architectures that use ACPI have support for
>  	 * PCI domains, so we indicate this in _OSC support capabilities.
> @@ -468,11 +474,6 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
>  		return;
>  	}
>  
> -	if (pcie_ports_disabled) {
> -		dev_info(&device->dev, "PCIe port services disabled; not requesting _OSC control\n");
> -		return;
> -	}
> -
>  	if ((support & ACPI_PCIE_REQ_SUPPORT) != ACPI_PCIE_REQ_SUPPORT) {
>  		decode_osc_support(root, "not requesting OS control; OS requires",
>  				   ACPI_PCIE_REQ_SUPPORT);
> -- 
> 2.7.4
>