linux-kernel - Re: [PATCH] pci: completely disable aspm if it's unsupported

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Message-ID: <20151203164007.GA16669@localhost>
Date:	Thu, 3 Dec 2015 10:40:07 -0600
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Josef Bacik <jbacik@...com>
Cc:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, bhelgaas@...gle.com, shli@...com,
	kernel-team@...com
Subject: Re: [PATCH] pci: completely disable aspm if it's unsupported

On Wed, Nov 18, 2015 at 09:25:03AM -0500, Josef Bacik wrote:
> We have some hardware that takes about 30 seconds to setup common clocks for
> ASPM, but our bios'es don't actually allow ASPM.  It seems we had this thing in
> place where we would disable ASPM after the pci bus probe so that we would make
> sure that pre pcie 1.1 devices would be properly skipped during initialization.
> This is because the mechanism to disable ASPM doesn't actually disable the
> setting up of the link state stuff, it just keeps us from changing the link
> state after the fact.  So instead make it so that when we call pcie_no_aspm()
> that we disable ASPM completley, that is we skip setting up the link state and
> everything.  This way we avoid the costly setup for a feature we cannot support
> in the first place and we also make sure we are safe from future tampering with
> the ASPM link state.  Thanks,

> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 317e355..5f84af2 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -954,6 +954,7 @@ void pcie_no_aspm(void)
>  	if (!aspm_force) {
>  		aspm_policy = POLICY_DEFAULT;
>  		aspm_disabled = 1;
> +		aspm_support_enabled = false;

After this patch, I think aspm_disabled and aspm_support_enabled are
equivalent.  If that's the case, we should get rid of one of them.

>  	}
>  }
>  
> -- 
> 2.1.0
> 
> --
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