From 139d081384c2f613ac74b372cb7afe2386d556e4 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Pali=20Roh=C3=A1r?= Date: Tue, 25 May 2021 19:42:38 +0200 Subject: [PATCH] serial: a37xx: Fix parent clock rate value and divider calculation MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit UART parent clock is by default the platform's xtal clock, which is 25 MHz. The value defined in the driver, though, is 25.8048 MHz. This is a hack for the suboptimal divisor calculation Divisor = UART clock / (16 * baudrate) which does not use rounding division, resulting in a suboptimal value for divisor if the correct parent clock rate was used. Change the code for divisor calculation to round to closest value, i.e. Divisor = Round(UART clock / (16 * baudrate)) and change the parent clock rate value to that returned by get_ref_clk(). This makes A3720 UART stable at standard UART baudrates between 1800 and 230400. Signed-off-by: Pali Rohár Reviewed-by: Marek Behún Reviewed-by: Stefan Roese --- drivers/serial/serial_mvebu_a3700.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/drivers/serial/serial_mvebu_a3700.c b/drivers/serial/serial_mvebu_a3700.c index 8f404879a5..9e7e479f80 100644 --- a/drivers/serial/serial_mvebu_a3700.c +++ b/drivers/serial/serial_mvebu_a3700.c @@ -7,6 +7,7 @@ #include #include #include +#include struct mvebu_plat { void __iomem *base; @@ -29,8 +30,6 @@ struct mvebu_plat { #define UART_CTRL_RXFIFO_RESET 0x4000 #define UART_CTRL_TXFIFO_RESET 0x8000 -#define CONFIG_UART_BASE_CLOCK 25804800 - static int mvebu_serial_putc(struct udevice *dev, const char ch) { struct mvebu_plat *plat = dev_get_plat(dev); @@ -75,12 +74,15 @@ static int mvebu_serial_setbrg(struct udevice *dev, int baudrate) { struct mvebu_plat *plat = dev_get_plat(dev); void __iomem *base = plat->base; + u32 parent_rate, divider; /* * Calculate divider * baudrate = clock / 16 / divider */ - writel(CONFIG_UART_BASE_CLOCK / baudrate / 16, base + UART_BAUD_REG); + parent_rate = get_ref_clk() * 1000000; + divider = DIV_ROUND_CLOSEST(parent_rate, baudrate * 16); + writel(divider, base + UART_BAUD_REG); /* * Set Programmable Oversampling Stack to 0, @@ -144,6 +146,7 @@ U_BOOT_DRIVER(serial_mvebu) = { static inline void _debug_uart_init(void) { void __iomem *base = (void __iomem *)CONFIG_DEBUG_UART_BASE; + u32 baudrate, parent_rate, divider; /* reset FIFOs */ writel(UART_CTRL_RXFIFO_RESET | UART_CTRL_TXFIFO_RESET, @@ -156,7 +159,10 @@ static inline void _debug_uart_init(void) * Calculate divider * baudrate = clock / 16 / divider */ - writel(CONFIG_UART_BASE_CLOCK / 115200 / 16, base + UART_BAUD_REG); + baudrate = 115200; + parent_rate = get_ref_clk() * 1000000; + divider = DIV_ROUND_CLOSEST(parent_rate, baudrate * 16); + writel(divider, base + UART_BAUD_REG); /* * Set Programmable Oversampling Stack to 0, -- 2.39.5