From a6d7514b14a6ea2a3868bdcb2fca7b2410738595 Mon Sep 17 00:00:00 2001 From: Dong Aisheng Date: Tue, 13 Jun 2017 10:55:54 +0800 Subject: [PATCH] tty: serial: lpuart: add a more accurate baud rate calculation method On new LPUART versions, the oversampling ratio for the receiver can be changed from 4x (00011) to 32x (11111) which could help us get a more accurate baud rate divider. The idea is to use the best OSR (over-sampling rate) possible. Note, OSR is typically hard-set to 16 in other LPUART instantiations. Loop to find the best OSR value possible, one that generates minimum baud diff iterate through the rest of the supported values of OSR. Cc: Greg Kroah-Hartman Cc: Jiri Slaby Cc: Stefan Agner Cc: Mingkai Hu Cc: Yangbo Lu Acked-by: Fugang Duan Signed-off-by: Dong Aisheng Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/fsl_lpuart.c | 79 ++++++++++++++++++++++++++++++--- 1 file changed, 72 insertions(+), 7 deletions(-) diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c index a0f2666d30cf..343de8c384b0 100644 --- a/drivers/tty/serial/fsl_lpuart.c +++ b/drivers/tty/serial/fsl_lpuart.c @@ -140,6 +140,8 @@ #define UARTBAUD_SBNS 0x00002000 #define UARTBAUD_SBR 0x00000000 #define UARTBAUD_SBR_MASK 0x1fff +#define UARTBAUD_OSR_MASK 0x1f +#define UARTBAUD_OSR_SHIFT 24 #define UARTSTAT_LBKDIF 0x80000000 #define UARTSTAT_RXEDGIF 0x40000000 @@ -1510,6 +1512,75 @@ lpuart_set_termios(struct uart_port *port, struct ktermios *termios, spin_unlock_irqrestore(&sport->port.lock, flags); } +static void +lpuart32_serial_setbrg(struct lpuart_port *sport, unsigned int baudrate) +{ + u32 sbr, osr, baud_diff, tmp_osr, tmp_sbr, tmp_diff, tmp; + u32 clk = sport->port.uartclk; + + /* + * The idea is to use the best OSR (over-sampling rate) possible. + * Note, OSR is typically hard-set to 16 in other LPUART instantiations. + * Loop to find the best OSR value possible, one that generates minimum + * baud_diff iterate through the rest of the supported values of OSR. + * + * Calculation Formula: + * Baud Rate = baud clock / ((OSR+1) × SBR) + */ + baud_diff = baudrate; + osr = 0; + sbr = 0; + + for (tmp_osr = 4; tmp_osr <= 32; tmp_osr++) { + /* calculate the temporary sbr value */ + tmp_sbr = (clk / (baudrate * tmp_osr)); + if (tmp_sbr == 0) + tmp_sbr = 1; + + /* + * calculate the baud rate difference based on the temporary + * osr and sbr values + */ + tmp_diff = clk / (tmp_osr * tmp_sbr) - baudrate; + + /* select best values between sbr and sbr+1 */ + tmp = clk / (tmp_osr * (tmp_sbr + 1)); + if (tmp_diff > (baudrate - tmp)) { + tmp_diff = baudrate - tmp; + tmp_sbr++; + } + + if (tmp_diff <= baud_diff) { + baud_diff = tmp_diff; + osr = tmp_osr; + sbr = tmp_sbr; + + if (!baud_diff) + break; + } + } + + /* handle buadrate outside acceptable rate */ + if (baud_diff > ((baudrate / 100) * 3)) + dev_warn(sport->port.dev, + "unacceptable baud rate difference of more than 3%%\n"); + + tmp = lpuart32_read(&sport->port, UARTBAUD); + + if ((osr > 3) && (osr < 8)) + tmp |= UARTBAUD_BOTHEDGE; + + tmp &= ~(UARTBAUD_OSR_MASK << UARTBAUD_OSR_SHIFT); + tmp |= (((osr-1) & UARTBAUD_OSR_MASK) << UARTBAUD_OSR_SHIFT); + + tmp &= ~UARTBAUD_SBR_MASK; + tmp |= sbr & UARTBAUD_SBR_MASK; + + tmp &= ~(UARTBAUD_TDMAE | UARTBAUD_RDMAE); + + lpuart32_write(&sport->port, tmp, UARTBAUD); +} + static void lpuart32_set_termios(struct uart_port *port, struct ktermios *termios, struct ktermios *old) @@ -1519,7 +1590,6 @@ lpuart32_set_termios(struct uart_port *port, struct ktermios *termios, unsigned long ctrl, old_ctrl, bd, modem; unsigned int baud; unsigned int old_csize = old ? old->c_cflag & CSIZE : CS8; - unsigned int sbr; ctrl = old_ctrl = lpuart32_read(&sport->port, UARTCTRL); bd = lpuart32_read(&sport->port, UARTBAUD); @@ -1616,12 +1686,7 @@ lpuart32_set_termios(struct uart_port *port, struct ktermios *termios, lpuart32_write(&sport->port, old_ctrl & ~(UARTCTRL_TE | UARTCTRL_RE), UARTCTRL); - sbr = sport->port.uartclk / (16 * baud); - bd &= ~UARTBAUD_SBR_MASK; - bd |= sbr & UARTBAUD_SBR_MASK; - bd |= UARTBAUD_BOTHEDGE; - bd &= ~(UARTBAUD_TDMAE | UARTBAUD_RDMAE); - lpuart32_write(&sport->port, bd, UARTBAUD); + lpuart32_serial_setbrg(sport, baud); lpuart32_write(&sport->port, modem, UARTMODIR); lpuart32_write(&sport->port, ctrl, UARTCTRL); /* restore control register */ -- 2.20.1