tty: serial: lpuart: add a more accurate baud rate calculation method (a6d7514b) · Commits · 戴 / test

drivers/tty/serial/fsl_lpuart.c

+72 −7

Original line number	Diff line number	Diff line
		@@ -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 */

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