clk: Add Baikal-T1 CCU PLLs driver

Baikal-T1 is supposed to be supplied with a high-frequency external
oscillator. But in order to create signals suitable for each IP-block
embedded into the SoC the oscillator output is primarily connected to
a set of CCU PLLs. There are five of them to create clocks for the MIPS
P5600 cores, an embedded DDR controller, SATA, Ethernet and PCIe domains.
The last three domains though named by the biggest system interfaces in
fact include nearly all of the rest SoC peripherals. Each of the PLLs is
based on True Circuits TSMC CLN28HPM IP-core with an interface wrapper
(so called safe PLL' clocks switcher) to simplify the PLL configuration
procedure.

This driver creates the of-based hardware clocks to use them then in
the corresponding subsystems. In order to simplify the driver code we
split the functionality up into the PLLs clocks operations and hardware
clocks declaration/registration procedures.

Even though the PLLs are based on the same IP-core, they may have some
differences. In particular, some CCU PLLs support the output clock change
without gating them (like CPU or PCIe PLLs), while the others don't, some
CCU PLLs are critical and aren't supposed to be gated. In order to cover
all of these cases the hardware clocks driver is designed with an
info-descriptor pattern. So there are special static descriptors declared
for each PLL, which is then used to create a hardware clock with proper
operations. Additionally debugfs-files are provided for each PLL' field
to make sure the implemented rate-PLLs-dividers calculation algorithm is
correct.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: devicetree@vger.kernel.org
Link: https://lore.kernel.org/r/20200526222056.18072-4-Sergey.Semin@baikalelectronics.ru
[sboyd@kernel.org: Silence sparse warning about initializing structs
with NULL vs. integer]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

1 files changed, 30 insertions, 0 deletions

diff --git a/drivers/clk/baikal-t1/Kconfig b/drivers/clk/baikal-t1/Kconfig
new file mode 100644
index 000000000000..00398ee916dc
--- /dev/null
+++ b/drivers/clk/baikal-t1/Kconfig
@@ -0,0 +1,30 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config CLK_BAIKAL_T1
+	bool "Baikal-T1 Clocks Control Unit interface"
+	depends on (MIPS_BAIKAL_T1 && OF) || COMPILE_TEST
+	default MIPS_BAIKAL_T1
+	help
+	  Clocks Control Unit is the core of Baikal-T1 SoC System Controller
+	  responsible for the chip subsystems clocking and resetting. It
+	  consists of multiple global clock domains, which can be reset by
+	  means of the CCU control registers. These domains and devices placed
+	  in them are fed with clocks generated by a hierarchy of PLLs,
+	  configurable and fixed clock dividers. Enable this option to be able
+	  to select Baikal-T1 CCU PLLs and Dividers drivers.
+
+if CLK_BAIKAL_T1
+
+config CLK_BT1_CCU_PLL
+	bool "Baikal-T1 CCU PLLs support"
+	select MFD_SYSCON
+	default MIPS_BAIKAL_T1
+	help
+	  Enable this to support the PLLs embedded into the Baikal-T1 SoC
+	  System Controller. These are five PLLs placed at the root of the
+	  clocks hierarchy, right after an external reference oscillator
+	  (normally of 25MHz). They are used to generate high frequency
+	  signals, which are either directly wired to the consumers (like
+	  CPUs, DDR, etc.) or passed over the clock dividers to be only
+	  then used as an individual reference clock of a target device.
+
+endif