ARM: at91: spl: Add mck function to lower rate while switching

Refer to the commit 70f8c8316ad(PMC: add new mck function to lower
rate while switching) from AT91Bootstrap.

While switching to a lower clock source, we must switch the clock
source first instead of last. Otherwise, we could end up with
too high frequency on internal bus and peripherals.
This happens on SAMA5D2 as exitting from the ROM code.

Add a function pmc_mck_init_down() to allow this sequence.

Signed-off-by: Wenyou Yang <wenyou.yang@microchip.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/arm/mach-at91/armv7/clock.c

@@ -150,6 +150,48 @@ void at91_mck_init(u32 mckr)
 		;
 }
 
+/*
+ * For the Master Clock Controller Register(MCKR), while switching
+ * to a lower clock source, we must switch the clock source first
+ * instead of last. Otherwise, we could end up with too high frequency
+ * on the internal bus and peripherals.
+ */
+void at91_mck_init_down(u32 mckr)
+{
+	struct at91_pmc *pmc = (struct at91_pmc *)ATMEL_BASE_PMC;
+	u32 tmp;
+
+	tmp = readl(&pmc->mckr);
+	tmp &= (~AT91_PMC_MCKR_CSS_MASK);
+	tmp |= (mckr & AT91_PMC_MCKR_CSS_MASK);
+	writel(tmp, &pmc->mckr);
+
+	while (!(readl(&pmc->sr) & AT91_PMC_MCKRDY))
+		;
+
+#ifdef CPU_HAS_H32MXDIV
+	tmp = readl(&pmc->mckr);
+	tmp &= (~AT91_PMC_MCKR_H32MXDIV);
+	tmp |= (mckr & AT91_PMC_MCKR_H32MXDIV);
+	writel(tmp, &pmc->mckr);
+#endif
+
+	tmp = readl(&pmc->mckr);
+	tmp &= (~AT91_PMC_MCKR_PLLADIV_MASK);
+	tmp |= (mckr & AT91_PMC_MCKR_PLLADIV_MASK);
+	writel(tmp, &pmc->mckr);
+
+	tmp = readl(&pmc->mckr);
+	tmp &= (~AT91_PMC_MCKR_MDIV_MASK);
+	tmp |= (mckr & AT91_PMC_MCKR_MDIV_MASK);
+	writel(tmp, &pmc->mckr);
+
+	tmp = readl(&pmc->mckr);
+	tmp &= (~AT91_PMC_MCKR_PRES_MASK);
+	tmp |= (mckr & AT91_PMC_MCKR_PRES_MASK);
+	writel(tmp, &pmc->mckr);
+}
+
 int at91_enable_periph_generated_clk(u32 id, u32 clk_source, u32 div)
 {
 	struct at91_pmc *pmc = (struct at91_pmc *)ATMEL_BASE_PMC;

arch/arm/mach-at91/include/mach/at91_common.h

@@ -25,6 +25,7 @@ void at91_lcd_hw_init(void);
 void at91_plla_init(u32 pllar);
 void at91_pllb_init(u32 pllar);
 void at91_mck_init(u32 mckr);
+void at91_mck_init_down(u32 mckr);
 void at91_pmc_init(void);
 void mem_init(void);
 void at91_phy_reset(void);