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Subject: Re: How to enable auto-suspend by default
To:     Mika Westerberg <mika.westerberg@linux.intel.com>,
        "Limonciello, Mario" <Mario.Limonciello@dell.com>
Cc:     Greg KH <gregkh@linuxfoundation.org>,
        Bastien Nocera <hadess@hadess.net>,
        Linux PM <linux-pm@vger.kernel.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
        Mathias Nyman <mathias.nyman@linux.intel.com>
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 <20201110172517.GC2495@lahna.fi.intel.com>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <30957f1a-1fe5-5d9a-101b-25f12fb93907@redhat.com>
Date:   Wed, 11 Nov 2020 12:27:32 +0100
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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.

> 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.

Note the deny-list + enable anything not on it approach could be done
either in the kernel or in a udev-rule + hwdb combo.

Regards,

Hans