clk: microchip: mpfs: add RTCREF clock control

The reference clock used by the PolarFire SoC's onboard rtc was missing
from the clock driver. Add this clock at the "config" clock level, with
the external reference clock as its parent.

Fixes: 635e5e7 ("clk: microchip: Add driver for Microchip PolarFire SoC")
Reviewed-by: Daire McNamara <daire.mcnamara@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20220413075835.3354193-9-conor.dooley@microchip.com
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/microchip/clk-mpfs.c

@@ -15,6 +15,7 @@
 #define REG_MSSPLL_POSTDIV_CR	0x10u
 #define REG_MSSPLL_SSCG_2_CR	0x2Cu
 #define REG_CLOCK_CONFIG_CR	0x08u
+#define REG_RTC_CLOCK_CR	0x0Cu
 #define REG_SUBBLK_CLOCK_CR	0x84u
 #define REG_SUBBLK_RESET_CR	0x88u
 
@@ -96,6 +97,17 @@ static const struct clk_div_table mpfs_div_ahb_table[] = {
 	{ 0, 0 }
 };
 
+/*
+ * The only two supported reference clock frequencies for the PolarFire SoC are
+ * 100 and 125 MHz, as the rtc reference is required to be 1 MHz.
+ * It therefore only needs to have divider table entries corresponding to
+ * divide by 100 and 125.
+ */
+static const struct clk_div_table mpfs_div_rtcref_table[] = {
+	{ 100, 100 }, { 125, 125 },
+	{ 0, 0 }
+};
+
 static unsigned long mpfs_clk_msspll_recalc_rate(struct clk_hw *hw, unsigned long prate)
 {
 	struct mpfs_msspll_hw_clock *msspll_hw = to_mpfs_msspll_clk(hw);
@@ -234,6 +246,16 @@ static struct mpfs_cfg_hw_clock mpfs_cfg_clks[] = {
 		REG_CLOCK_CONFIG_CR),
 	CLK_CFG(CLK_AHB, "clk_ahb", "clk_msspll", 4, 2, mpfs_div_ahb_table, 0,
 		REG_CLOCK_CONFIG_CR),
+	{
+		.cfg.id = CLK_RTCREF,
+		.cfg.shift = 0,
+		.cfg.width = 12,
+		.cfg.table = mpfs_div_rtcref_table,
+		.cfg.reg_offset = REG_RTC_CLOCK_CR,
+		.cfg.flags = CLK_DIVIDER_ONE_BASED,
+		.hw.init =
+			CLK_HW_INIT_PARENTS_DATA("clk_rtcref", mpfs_ext_ref, &mpfs_clk_cfg_ops, 0),
+	}
 };
 
 static int mpfs_clk_register_cfg(struct device *dev, struct mpfs_cfg_hw_clock *cfg_hw,
@@ -359,7 +381,7 @@ static struct mpfs_periph_hw_clock mpfs_periph_clks[] = {
 	CLK_PERIPH(CLK_MAC0, "clk_periph_mac0", PARENT_CLK(AHB), 1, 0),
 	CLK_PERIPH(CLK_MAC1, "clk_periph_mac1", PARENT_CLK(AHB), 2, 0),
 	CLK_PERIPH(CLK_MMC, "clk_periph_mmc", PARENT_CLK(AHB), 3, 0),
-	CLK_PERIPH(CLK_TIMER, "clk_periph_timer", PARENT_CLK(AHB), 4, 0),
+	CLK_PERIPH(CLK_TIMER, "clk_periph_timer", PARENT_CLK(RTCREF), 4, 0),
 	CLK_PERIPH(CLK_MMUART0, "clk_periph_mmuart0", PARENT_CLK(AHB), 5, CLK_IS_CRITICAL),
 	CLK_PERIPH(CLK_MMUART1, "clk_periph_mmuart1", PARENT_CLK(AHB), 6, 0),
 	CLK_PERIPH(CLK_MMUART2, "clk_periph_mmuart2", PARENT_CLK(AHB), 7, 0),