Date:   Mon, 23 Nov 2020 14:54:19 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     "Limonciello, Mario" <Mario.Limonciello@...l.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Bastien Nocera <hadess@...ess.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>
Subject: Re: How to enable auto-suspend by default

Hi,

On 11/11/20 3:31 PM, Mika Westerberg wrote:
> On Wed, Nov 11, 2020 at 12:27:32PM +0100, Hans de Goede wrote:
>> Hi,
>>
>> On 11/10/20 6:25 PM, Mika Westerberg wrote:
>>> On Tue, Nov 10, 2020 at 04:02:33PM +0000, Limonciello, Mario wrote:
>>>>>
>>>>> On Tue, Nov 10, 2020 at 11:57:07AM +0100, Bastien Nocera wrote:
>>>>>> Hey,
>>>>>>
>>>>>> systemd has been shipping this script to enable auto-suspend on a
>>>>>> number of USB and PCI devices:
>>>>>>
>>>>> https://github.com/systemd/systemd/blob/master/tools/chromiumos/gen_autosuspen
>>>>> d_rules.py
>>>>>>
>>>>>> The problem here is twofold. First, the list of devices is updated from
>>>>>> ChromeOS, and the original list obviously won't be updated by ChromeOS
>>>>>> developers unless a device listed exists in a ChromeBook computer,
>>>>>> which means a number of devices that do support autosuspend aren't
>>>>>> listed.
>>>>>>
>>>>>> The other problem is that this list needs to exist at all, and that it
>>>>>> doesn't seem possible for device driver developers (at various levels
>>>>>> of the stack) to opt-in to auto-suspend when all the variants of the
>>>>>> device (or at least detectable ones) support auto-suspend.
>>>>>
>>>>> A driver can say they support autosuspend today, but I think you are
>>>>> concerned about the devices that are controlled by class-compliant
>>>>> drivers, right?  And for those, no, we can't do this in the kernel as
>>>>> there are just too many broken devices out there.
>>>>>
>>>>
>>>> I guess what Bastien is getting at is for newer devices supported by class
>>>> drivers rather than having to store an allowlist in udev rules, can we set
>>>> the allowlist in the kernel instead.  Then distributions that either don't
>>>> use systemd or don't regularly update udev rules from systemd can take
>>>> advantage of better defaults on modern hardware.
>>>>
>>>> The one item that stood out to me in that rules file was 8086:a0ed.
>>>> It's listed as "Volteer XHCI", but that same device ID is actually present
>>>> in an XPS 9310 in front of me as well and used by the xhci-pci kernel module.
>>>>
>>>> Given we're effectively ending up with the combination of runtime PM turned
>>>> on by udev rules, do we need something like this for that ID:
>>>>
>>>> https://github.com/torvalds/linux/commit/6a7c533d4a1854f54901a065d8c672e890400d8a
>>>>
>>>> @Mika Westerberg should 8086:a0ed be quirked like the TCSS xHCI too?
>>>
>>> I think this one is the TGL PCH xHCI. The quirk currently for xHCI
>>> controllers that are part of the TCSS (Type-C SubSystem) where it is
>>> important to put all devices into low power mode whenever possible,
>>> otherwise it keeps the whole block on.
>>
>> Note that there are currently some IDs missing from the xHCIs which
>> are part of the TCSS too. At least the id for the xHCI in the thunderbolt
>> controller on the Lenovo T14 gen 1 is missing. I started a discussion
>> about extending the kernel quirk list for this vs switching to hwdb
>> a while a go:
>>
>> https://lore.kernel.org/linux-usb/b8b21ba3-0a8a-ff54-5e12-cf8960651086@redhat.com/
>>
>> The conclusion back then was to switch to hwdb, but I never got around to this.
> 
> The reason I've added these to the xHCI driver is that it works even if
> you are running some really small userspace (like busybox). Also for the
> xHCI in TCSS we know for sure that it fully supports D3cold.
> 
> (The one you refer above is actually mistake from my side as I never
>  tested Alpine Ridge LP controller which I think this is).

Ok, so I'll submit a patch adding the 15c1 product-id for the
INTEL_ALPINE_RIDGE_LP_2C_XHCI controller to the list of ids for which we
set the XHCI_DEFAULT_PM_RUNTIME_ALLOW quirk. To fix the much too high
idle-power consumption problem on devices with this Alpine Ridge variant.

>>> Typically we haven't done that for PCH side xHCI controllers though, but
>>> I don't see why not if it works that is. Adding Mathias to comment more
>>> on that since he is the xHCI maintainer.
>>
>> If we are also going to enable this for the non TCSS Intel XHCI controllers,
>> maybe just uncondtionally enable it for all Intel XHCI controllers, or
>> if necessary do a deny-list for some older models and enable it for anything
>> not on the deny-list (so all newer models). That should avoid the game of
>> whack-a-mole which we will have with this otherwise.
> 
> This is really up to Mathias to decide. I'm fine either way :)

Ok, Matthias what do you think about this?

Regards,

Hans

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