Date:   Sun, 10 Apr 2022 11:16:50 +0200
From:   Thorsten Leemhuis <regressions@...mhuis.info>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     Linux PCI <linux-pci@...r.kernel.org>,
        Stefan Gottwald <gottwald@...l.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI: PM: Quirk bridge D3 on Elo i2

On 09.04.22 15:35, Rafael J. Wysocki wrote:
> On Fri, Apr 8, 2022 at 9:53 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>>
>> On Mon, Apr 04, 2022 at 04:46:14PM +0200, Rafael J. Wysocki wrote:
>>> On Fri, Apr 1, 2022 at 1:34 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>>>> On Thu, Mar 31, 2022 at 11:57 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>>>>> On Thu, Mar 31, 2022 at 07:38:51PM +0200, Rafael J. Wysocki wrote:
>>>>>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>>>>>
>>>>>> If one of the PCIe root ports on Elo i2 is put into D3cold and then
>>>>>> back into D0, the downstream device becomes permanently inaccessible,
>>>>>> so add a bridge D3 DMI quirk for that system.
>>>>>>
>>>>>> This was exposed by commit 14858dcc3b35 ("PCI: Use
>>>>>> pci_update_current_state() in pci_enable_device_flags()"), but before
>>>>>> that commit the root port in question had never been put into D3cold
>>>>>> for real due to a mismatch between its power state retrieved from the
>>>>>> PCI_PM_CTRL register (which was accessible even though the platform
>>>>>> firmware indicated that the port was in D3cold) and the state of an
>>>>>> ACPI power resource involved in its power management.
>>>>>
>>>>> In the bug report you suspect a firmware issue.  Any idea what that
>>>>> might be?  It looks like a Gemini Lake Root Port, so I wouldn't think
>>>>> it would be a hardware issue.
>>>>
>>>> The _ON method of the ACPI power resource associated with the root
>>>> port doesn't work correctly.
>>>>
>>>>> Weird how things come in clumps.  Was just looking at Mario's patch,
>>>>> which also has to do with bridges and D3.
>>>>>
>>>>> Do we need a Fixes line?  E.g.,
>>>>>
>>>>>   Fixes: 14858dcc3b35 ("PCI: Use pci_update_current_state() in pci_enable_device_flags()")
>>>>
>>>> Strictly speaking, it is not a fix for the above commit.
>>>>
>>>> It is a workaround for a firmware issue uncovered by it which wasn't
>>>> visible, because power management was not used correctly on the
>>>> affected system because of another firmware problem addressed by
>>>> 14858dcc3b35.  It wouldn't have worked anyway had it been attempted
>>>> AFAICS.
>>>>
>>>> I was thinking about CCing this change to -stable instead.
>>
>> Makes sense, thanks.
>>
>>>>>> BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=215715
>>>>>> Reported-by: Stefan Gottwald <gottwald@...l.com>
>>>>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>>>>> ---
>>>>>>  drivers/pci/pci.c |   10 ++++++++++
>>>>>>  1 file changed, 10 insertions(+)
>>>>>>
>>>>>> Index: linux-pm/drivers/pci/pci.c
>>>>>> ===================================================================
>>>>>> --- linux-pm.orig/drivers/pci/pci.c
>>>>>> +++ linux-pm/drivers/pci/pci.c
>>>>>> @@ -2920,6 +2920,16 @@ static const struct dmi_system_id bridge
>>>>>>                       DMI_MATCH(DMI_BOARD_VENDOR, "Gigabyte Technology Co., Ltd."),
>>>>>>                       DMI_MATCH(DMI_BOARD_NAME, "X299 DESIGNARE EX-CF"),
>>>>>>               },
>>>>>> +             /*
>>>>>> +              * Downstream device is not accessible after putting a root port
>>>>>> +              * into D3cold and back into D0 on Elo i2.
>>>>>> +              */
>>>>>> +             .ident = "Elo i2",
>>>>>> +             .matches = {
>>>>>> +                     DMI_MATCH(DMI_SYS_VENDOR, "Elo Touch Solutions"),
>>>>>> +                     DMI_MATCH(DMI_PRODUCT_NAME, "Elo i2"),
>>>>>> +                     DMI_MATCH(DMI_PRODUCT_VERSION, "RevB"),
>>>>>> +             },
>>>>>
>>>>> Is this bridge_d3_blacklist[] similar to the PCI_DEV_FLAGS_NO_D3 bit?
>>>>
>>>> Not really.  The former applies to the entire platform and not to an
>>>> individual device.
>>>>
>>>>> Could they be folded together?  We have a lot of bits that seem
>>>>> similar but maybe not exactly the same (dev->bridge_d3,
>>>>> dev->no_d3cold, dev->d3cold_allowed, dev->runtime_d3cold,
>>>>> PCI_DEV_FLAGS_NO_D3, pci_bridge_d3_force, etc.)  Ugh.
>>>>
>>>> Yes, I agree that this needs to be cleaned up.
>>>>
>>>>> bridge_d3_blacklist[] itself was added by 85b0cae89d52 ("PCI:
>>>>> Blacklist power management of Gigabyte X299 DESIGNARE EX PCIe ports"),
>>>>> which honestly looks kind of random, i.e., it doesn't seem to be
>>>>> working around a hardware or even a firmware defect.
>>>>>
>>>>> Apparently the X299 issue is that 00:1c.4 is connected to a
>>>>> Thunderbolt controller, and the BIOS keeps the Thunderbolt controller
>>>>> powered off unless something is attached to it?  At least, 00:1c.4
>>>>> leads to bus 05, and in the dmesg log attached to [1] shows no devices
>>>>> on bus 05.
>>>>>
>>>>> It also says the platform doesn't support PCIe native hotplug, which
>>>>> matches what Mika said about it using ACPI hotplug.  If a system is
>>>>> using ACPI hotplug, it seems like maybe *that* should prevent us from
>>>>> putting things in D3cold?  How can we know whether ACPI hotplug
>>>>> depends on a certain power state?
>>>>
>>>> We have this check in pci_bridge_d3_possible():
>>>>
>>>> if (bridge->is_hotplug_bridge && !pciehp_is_native(bridge))
>>>>             return false;
>>>>
>>>> but this only applies to the case when the particular bridge itself is
>>>> a hotplug one using ACPI hotplug.
>>>>
>>>> If ACPI hotplug is used, it generally is unsafe to put PCIe ports into
>>>> D3cold, because in that case it is unclear what the platform
>>>> firmware's assumptions regarding control of the config space are.
>>>>
>>>> However, I'm not sure how this is related to the patch at hand.
>>>
>>> So I'm not sure how you want to proceed here.
>>>
>>> The platform is quirky, so the quirk for it will need to be added this
>>> way or another.  The $subject patch adds it using the existing
>>> mechanism, which is the least intrusive way.
>>>
>>> You seem to be thinking that the existing mechanism may not be
>>> adequate, but I'm not sure for what reason and anyway I think that it
>>> can be adjusted after adding the quirk.
>>>
>>> Please let me know what you think.
>>
>> I don't understand all that's going on here, but I applied it to
>> pci/pm for v5.19, thanks!
> Thank you!

Sorry, but this made me wonder: why v5.19? It's a regression exposed in
v5.15, so it afaics would be good to get this in this cycle -- and also
backported to v5.15.y, but it seem a tag to take care of that is
missing. :-/

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)

P.S.: As the Linux kernel's regression tracker I'm getting a lot of
reports on my table. I can only look briefly into most of them and lack
knowledge about most of the areas they concern. I thus unfortunately
will sometimes get things wrong or miss something important. I hope
that's not the case here; if you think it is, don't hesitate to tell me
in a public reply, it's in everyone's interest to set the public record
straight.

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