platform/x86: intel_pmc_core: Ignore GBE LTR on Tiger Lake platforms

platform/x86: intel_pmc_core: Ignore GBE LTR on Tiger Lake platforms

[ Upstream commit d1635448f1105e549b4041aab930dbc6945fc635 ]

Due to a HW limitation, the Latency Tolerance Reporting (LTR) value
programmed in the Tiger Lake GBE controller is not large enough to allow
the platform to enter Package C10, which in turn prevents the platform from
achieving its low power target during suspend-to-idle.  Ignore the GBE LTR
value on Tiger Lake. LTR ignore functionality is currently performed solely
by a debugfs write call. Split out the LTR code into its own function that
can be called by both the debugfs writer and by this work around.

Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Reviewed-by: Sasha Neftin <sasha.neftin@intel.com>
Cc: intel-wired-lan@lists.osuosl.org
Reviewed-by: Rajneesh Bhardwaj <irenic.rajneesh@gmail.com>
Link: https://lore.kernel.org/r/20210319201844.3305399-2-david.e.box@linux.intel.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>