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serial: stm32x7: simplify baud rate register calculation

Simplify baud rate register formula and use the oversampling
uart feature.
This code is aligned with what is implemented in kernel driver
drivers/tty/serial/stm32-usart.c since kernel v4.9.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Christophe KERELLO <christophe.kerello@st.com>
Reviewed-by: Patrick DELAUNAY <patrick.delaunay@st.com>
Acked-by: Vikas MANOCHA <vikas.manocha@st.com>
tags/2020-06-01
Patrice Chotard 4 years ago
committed by Tom Rini
parent
commit
1afcf9cb25
2 changed files with 17 additions and 7 deletions
  1. +15
    -6
      drivers/serial/serial_stm32x7.c
  2. +2
    -1
      drivers/serial/serial_stm32x7.h

+ 15
- 6
drivers/serial/serial_stm32x7.c View File

@@ -20,7 +20,7 @@ static int stm32_serial_setbrg(struct udevice *dev, int baudrate)
{
struct stm32x7_serial_platdata *plat = dev->platdata;
struct stm32_usart *const usart = plat->base;
u32 clock, int_div, frac_div, tmp;
u32 clock, int_div, mantissa, fraction, oversampling;

if (((u32)usart & STM32_BUS_MASK) == APB1_PERIPH_BASE)
clock = clock_get(CLOCK_APB1);
@@ -29,11 +29,20 @@ static int stm32_serial_setbrg(struct udevice *dev, int baudrate)
else
return -EINVAL;

int_div = (25 * clock) / (4 * baudrate);
tmp = ((int_div / 100) << USART_BRR_M_SHIFT) & USART_BRR_M_MASK;
frac_div = int_div - (100 * (tmp >> USART_BRR_M_SHIFT));
tmp |= (((frac_div * 16) + 50) / 100) & USART_BRR_F_MASK;
writel(tmp, &usart->brr);
int_div = DIV_ROUND_CLOSEST(clock, baudrate);

if (int_div < 16) {
oversampling = 8;
setbits_le32(&usart->cr1, USART_CR1_OVER8);
} else {
oversampling = 16;
clrbits_le32(&usart->cr1, USART_CR1_OVER8);
}

mantissa = (int_div / oversampling) << USART_BRR_M_SHIFT;
fraction = int_div % oversampling;

writel(mantissa | fraction, &usart->brr);

return 0;
}


+ 2
- 1
drivers/serial/serial_stm32x7.h View File

@@ -23,8 +23,9 @@ struct stm32_usart {
};


#define USART_CR1_RE (1 << 2)
#define USART_CR1_OVER8 (1 << 15)
#define USART_CR1_TE (1 << 3)
#define USART_CR1_RE (1 << 2)
#define USART_CR1_UE (1 << 0)

#define USART_CR3_OVRDIS (1 << 12)