drm/i915: Fix DDI PHY init if it was already on

drm/i915: Fix DDI PHY init if it was already on

The common lane power down flag of a DPIO PHY has a funky semantic:
after the initial enabling of the PHY (so from a disabled state) this
flag will be clear. It will be set only after the PHY will be used for
the first time (for instance due to enabling the corresponding pipe) and
then become unused (due to disabling the pipe). During the initial PHY
enablement we don't know which of the above phases we are in, so move
the check for the flag where this is known, the HW readout code. This is
where the rest of lane power down status checks are done anyway.

This fixes at least a problem on GLK where after module reloading, the
common lane power down flag of PHY1 is set, but the PHY is actually
powered-on and properly set up. The GRC readout code for other PHYs will
hence think that PHY1 is not powered initially and disable it after the
GRC readout. This will cause the AUX power well related to PHY1 to get
disabled in a stuck state, timing out when we try to enable it later.

Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Fixes: e93da0a0137b ("drm/i915/bxt: Sanitiy check the PHY lane power down status")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102777
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171002135307.26117-1-imre.deak@intel.com