linux-kernel - Re: [PATCH] PCI/PM: Skip link training delay for S3 resume

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Message-ID: <20200311102811.GA2540@lahna.fi.intel.com>
Date:   Wed, 11 Mar 2020 12:28:11 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI/PM: Skip link training delay for S3 resume

Hi,

On Wed, Mar 11, 2020 at 12:52:49PM +0800, Kai-Heng Feng wrote:
> Commit ad9001f2f411 ("PCI/PM: Add missing link delays required by the
> PCIe spec") added a 1100ms delay on resume for bridges that don't
> support Link Active Reporting.
> 
> The commit also states that the delay can be skipped for S3, as the
> firmware should already handled the case for us.

Delay can be skipped if the firmware provides _DSM with function 8
implemented according to PCI firmwre spec 3.2 sec 4.6.8.

> So let's skip the link training delay for S3, to save 1100ms resume
> time.
> 
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>  drivers/pci/pci-driver.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 0454ca0e4e3f..3050375bad04 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -916,7 +916,8 @@ static int pci_pm_resume_noirq(struct device *dev)
>  	pci_fixup_device(pci_fixup_resume_early, pci_dev);
>  	pcie_pme_root_status_cleanup(pci_dev);
>  
> -	if (!skip_bus_pm && prev_state == PCI_D3cold)
> +	if (!skip_bus_pm && prev_state == PCI_D3cold
> +	    && !pm_resume_via_firmware())

So this would need to check for the _DSM result as well. We do evaluate
it in pci_acpi_optimize_delay() (drivers/pci/pci-acpi.c) and that ends
up lowering ->d3cold_delay so maybe check that here.

>  		pci_bridge_wait_for_secondary_bus(pci_dev);
>  
>  	if (pci_has_legacy_pm_support(pci_dev))
> -- 
> 2.17.1