Devices on the Intel Lynxpoint Low Power Subsystem (LPSS) have some
common features that aren't shared with any other platform devices,
including the clock and LTR (Latency Tolerance Reporting) registers.
It is better to handle those features in common code than to bother
device drivers with doing that (I/O functionality-wise the LPSS
devices are generally compatible with other devices that don't
have those special registers and may be handled by the same drivers).

The clock registers of the LPSS devices are now taken care of by
the special clk-x86-lpss driver, but the MMIO mappings used for
accessing those registers can also be used for accessing the LTR
registers on those devices (LTR support for the Lynxpoint LPSS is
going to be added by a subsequent patch).  Thus it is convenient
to add a special ACPI scan handler for the Lynxpoint LPSS devices
that will create the MMIO mappings for accessing the clock (and
LTR in the future) registers and will register the LPSS devices'
clocks, so the clk-x86-lpss driver will only need to take care of
the main Lynxpoint LPSS clock.

Introduce a special ACPI scan handler for Intel Lynxpoint LPSS
devices as described above.  This also reduces overhead related to
browsing the ACPI namespace in search of the LPSS devices before the
registration of their clocks, removes some LPSS-specific (and
somewhat ugly) code from acpi_platform.c and shrinks the overall code
size slightly.
Signed-off-by: NMika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NMike Turquette <mturquette@linaro.org>

Intel Lynxpoint Low Power Subsystem hosts peripherals like UART, I2C and
SPI controllers. For most of these there is a configuration register that
allows software to enable and disable the functional clock. Disabling the
clock while the peripheral is not used saves power.

In order to take advantage of this we add a new clock gate of type
lpss_gate that just re-uses the ordinary clk_gate but in addition is able
to enumerate the base address register of the device using ACPI.

We then create a clock tree that models the Lynxpoint LPSS clocks using
these gates and fixed clocks so that we can pass clock rate to the drivers
as well.
Signed-off-by: NHeikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: NMika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: NMike Turquette <mturquette@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>