[GTALUG] beware CherryTrail and BayTrail systems

[D. Hugh Redelmeier]

Over the last few years, Intel has been improving the Atom line of 
processors.  Device manufacturers have been using these improved SoCs to 
create interesting low-end boxes.  There are two marketing pushes: Android 
and Windows.  Linux get a bit-part mention.

All these processors are 64 bits but some have only 32-bit firmware 
(UEFI).  None has a conventional old-style BIOS.

Examples that I have some experience with:

- Asus ZenPhone II cellphone (Android) (I think that later ZenPhones use 
  ARM)

- google nexus player (Android)

- Asus transformer T100TAF (32-bit Windows) (convertible tablet/netbook)

- Kangaroo little computer (64-bit Windows)

- Dell Venue 8 Pro (5830) (32-bit Windows)

- Acer Aspire E11 (ES1-11M-c0fq) notebook (64-bit Windows)

- HP Pro Tablet 608 G1 (64-bit Windows)

- for contrast: HP Stream Mini (64-bit Windows) (Haswell-based Celeron, 
  not Atom)

All these were about $200 or less -- kind of appealing.

Good Linux experiences:

- The Acer Aspire just worked under Linux.  I don't know why.  I have not 
  tried HDMI-out: sound may not work under Linux.  Sleep and all the 
  other goodies do.  I use it a lot.

- The Kangaroo will boot Fedora easily.  But I haven't tested much with 
  it -- I use it in Windows 10 because of Netflix + Shomi mess.

- HP Stream Mini just works.  It is even possible to add RAM up to
  16G and a 2.5 inch drive (with a magic cable that can be purchased
  from Hong Kong sellers).  But it is Haswell, not *Trail.

Bad Linux experiences:

I don't really know an easy way of installing a normal Linux distro on
an Android device.  So I haven't tried.

It takes hacking to get most Linux distros to boot under 32-bit UEFI.
Now Ubuntu multiarch supports it out-of-the-box, things are starting
to get better (as far as I'm concerned).  There had already been
projects to work around this limitation:
  <https://wiki.debian.org/InstallingDebianOn/Asus/T100TA>
  <https://www.happyassassin.net/fedlet-a-fedora-remix-for-bay-trail-tablets/>
  <https://plus.google.com/communities/117853703024346186936>
and more.

Even with that, there are plenty of problems with driver and power
management support.  The first link gives a nice scorecard.

There is a kernel bug in handling cstates (compute states for power
management) with BayTrail and CherryTrail.  This has been around for
over a year with no fix (initially it was thought to be a GPU driver
bug).  The bug appears to have been introduced by Intel.  For the life
of me, I don't know why they have not fixed it.
  <https://bugzilla.kernel.org/show_bug.cgi?id=109051>
I haven't experienced this bug on my Acer notebook, possibly because I
never watch videos on it.

Intel created a driver to handle sound over HDMI but never upstreamed
it so it no longer works.
<https://01.org/ubuntu-hdmi>

Most of these devices have 2G of RAM, 32G of eMMC (disk).  This
appears to be due to Microsoft licensing prices (free up to this
size, expensive above).  So there isn't really room for a dual-boot
Windows/Linux setup.  Before I install Linux, I want to try it to find
if it works well enough on this hardware.

On the T100TAF, there is a MicroSD drive.  I thought that I could
install Linux on that instead of replacing Windows on the eMMC.
Amazingly, there is no UEFI driver for the MicroSD so the machine won't boot
off MicroSD!  debian 8.4.0's install disk doesn't see it either so I cannot
install with most filesystems (except /boot) on the MicroSD.  Incredible.

CherryTrail is reputed to be very demanding of cooling and thus many
systems suffer badly from thermal throttling (the chip slows down to
cool off).  This is true in Windows.  I wonder how this works with
Linux when cstates are constrained to avoid the bug mentioned above.

The HP Pro Tablet 608 G1 was made for a much higher price-point (I
lucked into a cheap unit from Factory Direct).  It has 4G of RAM and
64G of eMMC.  But it has it's own bugs under Windows that HP has been
slow to fix.  For my purposes, one problem is that there is only one USB C
connector for power and for extra peripherals and HP won't let it act
for more than one role at once (the whole point of USB C).  They want
me to buy a dock that connects to a proprietary POGO plug, for $200.
No thanks.

Summary: beware when buying a *Trail device thinking that you can just
drop a normal Linux distro on it.

Bonus warning: There are some problems with Linux support for Skylake,
Intel's  most recent generation of mainstream processors.
I'm confident that they are being ironed out (Linus has a Skylake desktop).