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

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Message-Id: <ABD5242B-E118-4811-AA8A-DF7C2A3B2E8B@canonical.com>
Date:   Thu, 12 Mar 2020 17:45:32 +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



> On Mar 12, 2020, at 16:04, Mika Westerberg <mika.westerberg@...ux.intel.com> wrote:
> 
> On Thu, Mar 12, 2020 at 12:23:46PM +0800, Kai-Heng Feng wrote:
>> 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?
> 
> Actually I think pci_bridge_wait_for_secondary_bus() already takes it
> into account. Have you checked if the BIOS has this _DSM implemented in
> the first place?

-[0000:00]-+-00.0  Intel Corporation Device 9b44
           +-1c.0-[03-3b]----00.0-[04-3b]--+-00.0-[05]----00.0  Intel Corporation JHL7540 Thunderbolt 3 NHI [Titan Ridge 2C 2018]
           |                               +-01.0-[06-3a]--
           |                               \-02.0-[3b]----00.0  Intel Corporation JHL7540 Thunderbolt 3 USB Controller [Titan Ridge 2C 2018]

00:1c.0 has _DSM implemented.
How do I check for the Thunderbolt device?
It doesn't seem to have a fixed _ADR so I don't know how to locate it in DSDT/SSDT table.

Log with additional debug message:
[  948.813025] ACPI: EC: interrupt unblocked
[  948.925017] pcieport 0000:00:01.0: pcie_wait_for_link_delay sleep 1100ms
[  949.065466] pcieport 0000:04:00.0: pcie_wait_for_link_delay sleep 1100ms
[  949.065468] pcieport 0000:04:02.0: pcie_wait_for_link_delay sleep 1100ms

00:01.0 is the port for discrete graphics.

Kai-Heng