stm32g4:rcc: add uart peripheral clock source helpers

Required so that the common uart infrastructure can be updated. This was
the last family to receive this implementation.

Signed-off-by: Karl Palsson <karlp@tweak.au>

include/libopencm3/stm32/g4/rcc.h

@@ -1032,6 +1032,11 @@ uint32_t rcc_system_clock_source(void);
 void rcc_clock_setup_pll(const struct rcc_clock_scale *clock);
 void __attribute__((deprecated("Use rcc_clock_setup_pll as direct replacement"))) rcc_clock_setup_hse_3v3(const struct rcc_clock_scale *clock);
 void rcc_set_clock48_source(uint32_t clksel);
+/**
+ * Get the peripheral clock speed for the specified (LP)UxART
+ * @param usart Base address of USART to get clock frequency for.
+ */
+uint32_t rcc_get_usart_clk_freq(uint32_t usart);
 
 END_DECLS
 

lib/stm32/g4/rcc.c

@@ -763,4 +763,39 @@ void rcc_set_clock48_source(uint32_t clksel)
 	RCC_CCIPR |= (clksel << RCC_CCIPR_CLK48SEL_SHIFT);
 }
 
+static uint32_t rcc_get_clksel_freq(uint8_t shift) {
+	uint8_t clksel = (RCC_CCIPR >> shift) & RCC_CCIPR_SEL_MASK;
+	uint8_t hpre = (RCC_CFGR >> RCC_CFGR_HPRE_SHIFT) & RCC_CFGR_HPRE_MASK;
+	switch (clksel) {
+	case RCC_CCIPR_USARTxSEL_PCLK:
+		return rcc_apb1_frequency;
+	case RCC_CCIPR_USARTxSEL_SYSCLK:
+		return rcc_ahb_frequency * rcc_get_div_from_hpre(hpre);
+	case RCC_CCIPR_USARTxSEL_LSE:
+		return 32768;
+	case RCC_CCIPR_USARTxSEL_HSI16:
+		return 16000000U;
+	}
+	cm3_assert_not_reached();
+}
+
+
+uint32_t rcc_get_usart_clk_freq(uint32_t usart)
+{
+	if (usart == USART1_BASE) {
+		return rcc_get_clksel_freq(RCC_CCIPR_USART1SEL_SHIFT);
+	} else if (usart == USART2_BASE) {
+		return rcc_get_clksel_freq(RCC_CCIPR_USART2SEL_SHIFT);
+	} else if (usart == USART3_BASE) {
+		return rcc_get_clksel_freq(RCC_CCIPR_USART3SEL_SHIFT);
+	} else if (usart == UART4_BASE) {
+		return rcc_get_clksel_freq(RCC_CCIPR_UART4SEL_SHIFT);
+	} else if (usart == UART5_BASE) {
+		return rcc_get_clksel_freq(RCC_CCIPR_UART5SEL_SHIFT);
+	} else if (usart == LPUART1_BASE) {
+		return rcc_get_clksel_freq(RCC_CCIPR_LPUART1SEL_SHIFT);
+	}
+	cm3_assert_not_reached();
+}
+
 /**@}*/