[Bug 68451] [byt dsi] Baytrail/T DSI display not supported on ASUS T100TA

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=68451

--- Comment #45 from Robert R. Howell <rhowell at uwyo.edu> ---
(In reply to Jani Nikula from comment #44)
> The final DSI patches have been posted this week [1], not reviewed yet due
> to travel, but you're welcome to give them a go. Should apply on top of
> drm-intel-nightly of [2].
> 
> [1]
> http://mid.gmane.org/1397454507-10273-1-git-send-email-shobhit.kumar@intel.
> com
> 
> [2] http://cgit.freedesktop.org/drm-intel/

Thanks very much for providing the patches.  I have compiled and tested a new
x86_64 kernel using them, combined with the most recent 3.15 code.  That is
working reasonably well on an ASUS T100TA and also a Toshiba Encore 8.  With
these driver patches I can turn off and on the video on the tablet panels, and
the HDMI output works fine too.  

With the new patches xrandr reports the panel as device "UNKNOWN1" rather than
the former VGA1, which it now lists as unconnected.  So scripts which rely on
VGA1 need to be modified slightly.  With the the patches I no longer need the
kernel boot options "video=VGA-1..." and "drm_kms_helper.edid_firmware=..." and
I also no longer need to specify the resolution in the
/etc/X11/xorg.conf.d/50-monitor.conf file.  Although I haven't tried a system
install from scratch, that should required far less hand configuration than
before.

There are a few minor problems on the x86_64 systems.  For example dmesg shows
a moderate number of i915 warnings about "vblank_wait_timed_out", "pipe_off
wait timed out",  "pipe state doesn't match!", and a few others.  Earlier in
the boot process I also see a few errors like "drm:dpi_send_cmd] *ERROR*
Timeout waiting for DPI FIFO empty."  However at least on the x86_64 systems
they don't seem to cause problems.

I also tried installing a 32 bit (i386) kernel with the new patches on a T100TA
system and the results were quite different.  While the patches seem to restore
the functionality mentioned above, the system very quickly bogs down to an
unusably slow state and eventually freezes.  I think it is getting overwhelmed
by a larger number of warnings like those mentioned above.  Whatever is doing
it is clearly i915 related, as booting the system with nomodeset eliminates the
problem.

So in summary, despite a few glitches, on x86_64 kernels, for both T100TA's and
Toshiba Encore 8's, the patches work well and vastly simplify the special
configuration which otherwise needs to be done.

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