Bug#797949: linux: CONFIG_PINCTRL_BAYTRAIL=y needed for microSD slot to function on Intel Compute Stick

[Henry Hallam <deb@pericynthion.org>]

Source: linux
Version: 4.2-1~exp1
Severity: normal

Dear Maintainer,

   * What led up to the situation?
   Installing Debian jessie or sid on an Intel Compute Stick (STCK1A32WFC),
   a miniature amd64 system based on the Atom Z3735F system-on-chip
   
   * What exactly did you do (or not do) that was effective (or
     ineffective)?
   Tried to use the external Micro SDXC socket, which should appear as
   /dev/mmcblk1
   
   * What was the outcome of this action?
   /dev/mmcblk1 does not exist, only /dev/mmcblk0 (the internal eMMC)
   
   * What outcome did you expect instead?
   /dev/mmcblk1 exists and is usable.

I tried the following kernel packages which all present the same problem:
linux-image-3.16.0-4-amd64
linux-image-4.0.0-2-amd64
linux-image-4.1.0-2-amd64
linux-image-4.2.0-trunk-amd64

Suggested fix:

After some research into similar platforms I tried rebuilding the
kernel package with the CONFIG_PINCTRL_BAYTRAIL option enabled.  This
resolved the issue.  It appears to enable some kind of memory-mapped
GPIO that is required to set up or use the external MicroSD socket.

I have successfully tried this fix on the 4.0.0 and 4.1.0 kernel
packages from the unstable repository and 4.2.0 from the experimental
repository.  It does not work on 3.16.0 as the config option was
introduced in kernel version 3.19. 

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'stable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 4.2.0-2+baytrail.1-amd64
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Thanks,
Henry Hallam