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

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Message-Id: <2C20385C-4BA4-4D6D-935A-AFDB97FAB5ED@canonical.com>
Date:   Thu, 12 Mar 2020 12:23:46 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.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 Mar 11, 2020, at 18:28, Mika Westerberg <mika.westerberg@...ux.intel.com> wrote:
> 
> 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.

As someone who doesn't have access to the PCI spec...
Questions below.

> 
>> 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.

Do we need to wait for d3cold_delay here?
Or we can also skip that as long as pci_acpi_dsm_guid and FUNCTION_DELAY_DSM present?

Kai-Heng

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