clk: sifive: add a driver for the SiFive FU540 PRCI IP block

Add driver code for the SiFive FU540 PRCI IP block.  This IP block
handles reset and clock control for the SiFive FU540 device and
implements SoC-level clock tree controls and dividers.

Based on code written by Wesley Terpstra <wesley@sifive.com>:
https://github.com/riscv/riscv-linux/commit/999529edf517ed75b56659d456d221b2ee56bb60

Boot and PLL rate change were tested on a SiFive HiFive Unleashed
board.

This version includes several changes requested by Stephen Boyd
<sboyd@kernel.org>.

Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Wesley W. Terpstra <wesley@sifive.com>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Megan Wachs <megan@sifive.com>
Cc: linux-riscv@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-clk@vger.kernel.org
[sboyd@kernel.org: Fix some const and ARRAY_SIZE() issues, make makefile
only descend if CLK_SIFIVE=y]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/Kconfig

@@ -311,6 +311,7 @@ source "drivers/clk/mvebu/Kconfig"
 source "drivers/clk/qcom/Kconfig"
 source "drivers/clk/renesas/Kconfig"
 source "drivers/clk/samsung/Kconfig"
+source "drivers/clk/sifive/Kconfig"
 source "drivers/clk/sprd/Kconfig"
 source "drivers/clk/sunxi-ng/Kconfig"
 source "drivers/clk/tegra/Kconfig"

drivers/clk/Makefile

@@ -94,6 +94,7 @@ obj-$(CONFIG_COMMON_CLK_QCOM)		+= qcom/
 obj-y					+= renesas/
 obj-$(CONFIG_ARCH_ROCKCHIP)		+= rockchip/
 obj-$(CONFIG_COMMON_CLK_SAMSUNG)	+= samsung/
+obj-$(CONFIG_CLK_SIFIVE)		+= sifive/
 obj-$(CONFIG_ARCH_SIRF)			+= sirf/
 obj-$(CONFIG_ARCH_SOCFPGA)		+= socfpga/
 obj-$(CONFIG_PLAT_SPEAR)		+= spear/

drivers/clk/sifive/Kconfig

@@ -0,0 +1,18 @@
+# SPDX-License-Identifier: GPL-2.0
+
+menuconfig CLK_SIFIVE
+	bool "SiFive SoC driver support"
+	help
+	  SoC drivers for SiFive Linux-capable SoCs.
+
+if CLK_SIFIVE
+
+config CLK_SIFIVE_FU540_PRCI
+	bool "PRCI driver for SiFive FU540 SoCs"
+	select CLK_ANALOGBITS_WRPLL_CLN28HPC
+	help
+	  Supports the Power Reset Clock interface (PRCI) IP block found in
+	  FU540 SoCs.  If this kernel is meant to run on a SiFive FU540 SoC,
+	  enable this driver.
+
+endif

drivers/clk/sifive/Makefile

@@ -0,0 +1 @@
+obj-$(CONFIG_CLK_SIFIVE_FU540_PRCI)	+= fu540-prci.o