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From:   Tom Cook <tom.k.cook@gmail.com>
Date:   Mon, 4 Nov 2019 14:32:30 +0000
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Subject: Re: Power management - HP 15-ds0502na
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On Mon, Nov 4, 2019 at 1:51 PM Theodore Y. Ts'o <tytso@mit.edu> wrote:
> This is actually the laptop's ACPI and/or EC not supporting
> suspend-to-ram at all.  Suspend to idle is the new hotness, because it
> gives the OS much more control (but also gives the OS much more
> opportunity to screw up).  The Dell XPS 13 (models 9370 and 9380)
> supports both s2idle and s2ram, but s2idle doesn't work well at all on
> Linux.  (Well, at least not the upstream kernels; the official Dell
> Ubuntu kernel and userspace apparently has enough tweaks that it works
> well.)

s2idle sort of works - the thing appears to go to sleep and wake up
okay - but the power savings are not really enough to make it
worthwhile.  Putting it into s2idle state and putting it in a bag
results in a very hot laptop - and of course that makes battery life
not great.  I'm guessing this is the Ryzen 7 CPU idle states not being
very well supported?

> > * There are a few devices that appear to be on I2C buses and declared
> > in the ACPI tables (eg the fingerprint sensor) which don't show up
> > under Linux.  They did under Windows, until I blew the Windows
> > installation away to install Linux, and I'm assuming that Windows
> > found them through the ACPI DSDT.  Now thinking it may have been handy
> > to keep Windows around for debugging, but that's regrets for you.
>
> Even if they showed up, it's unclear the device driver would exist for
> Linux.  Most fingerprint readers have proprietary interfaces and
> aren't well supported by Linux in general.

Yes, understood.  But the first step would be enumerating them through
the ACPI tables (if indeed that is how they are announced).

> > Is this the right place to raise this?  If there's some other place
> > that Linux ACPI issues are dealt with, please point me there as I've
> > not had any luck googling.
>
> There is the linux-acpi@vger.kernel.org mailing list and the
> linux-pm@vger.kernel.org (pm --> "power management") where you might
> try asking about the s2idle.  A lot of the issues with s2idle appear
> to be very device driver specific, and not about the power management
> core, so it's unclear folks on those lists will be able to help.  But
> it's worth a try...

Thanks.

Tom