During state readout we first read out the pipe src size, store
that information in the user mode h/vdisplay, but later on we overwrite
that with the actual crtc timings. That makes our read out crtc state
inconsistent with itself when the BIOS has enabled the panel fitter to
scale the pipe contents. Let's preserve the pipe src size based
information in the user mode to make things consistent again.

This fixes a problem introduced by commit a2936e3d ("drm/i915:
Use drm_mode_get_hv_timing() to populate plane clip rectangle")
where the inconsistent state is now leading the plane clipping code
to report a failure on account the plane dst coordinates not matching
the user mode size. Previously we did the plane clipping based on
the pipe src size instead and thus never noticed the inconsistency.

The failure manifests as a WARN:
[    0.762117] [drm:intel_dump_pipe_config [i915]] requested mode:
[    0.762142] [drm:drm_mode_debug_printmodeline [drm]] Modeline 0:"1366x768" 60 72143 1366 1414 1446 1526 768 771 777 784 0x40 0xa
...
[    0.762327] [drm:intel_dump_pipe_config [i915]] port clock: 72143, pipe src size: 1024x768, pixel rate 72143
...
[    0.764666] [drm:drm_atomic_helper_check_plane_state [drm_kms_helper]] Plane must cover entire CRTC
[    0.764690] [drm:drm_rect_debug_print [drm]] dst: 1024x768+0+0
[    0.764711] [drm:drm_rect_debug_print [drm]] clip: 1366x768+0+0
[    0.764713] ------------[ cut here ]------------
[    0.764714] Could not determine valid watermarks for inherited state
[    0.764792] WARNING: CPU: 4 PID: 159 at drivers/gpu/drm/i915/intel_display.c:14584 intel_modeset_init+0x3ce/0x19d0 [i915]
...

Cc: FadeMind <fademind@gmail.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reported-by: FadeMind <fademind@gmail.com>
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Tested-by: Dave Jones <davej@codemonkey.org.uk>
References: https://lists.freedesktop.org/archives/intel-gfx/2018-April/163186.html
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105992
Fixes: a2936e3d ("drm/i915: Use drm_mode_get_hv_timing() to populate plane clip rectangle")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180426163015.14232-1-ville.syrjala@linux.intel.comReviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Larry Finger <Larry.Finger@lwfinger.net>
Tested-by: FadeMind <fademind@gmail.com>