On 2017-05-15 00:48, Dong Aisheng wrote:
> 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.
>
> Currently only i.MX7ULP is using it.
>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Jiri Slaby <jslaby@xxxxxxxx>
> Cc: Stefan Agner <stefan@xxxxxxxx>
> Cc: Mingkai Hu <Mingkai.Hu@xxxxxxx>
> Cc: Yangbo Lu <yangbo.lu@xxxxxxx>
> Acked-by: Fugang Duan <fugang.duan@xxxxxxx>
> Signed-off-by: Dong Aisheng <aisheng.dong@xxxxxxx>
> ---
> drivers/tty/serial/fsl_lpuart.c | 85 ++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 79 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
> index 107d0911..bda4b0c 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
> @@ -1506,6 +1508,72 @@ lpuart_set_termios(struct uart_port *port,
> struct ktermios *termios,
> }
>
> 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;
> + }
> + }
> +
> + /* 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.membase + 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(tmp, sport->port.membase + UARTBAUD);
> +}
> +
> +static void
> lpuart32_set_termios(struct uart_port *port, struct ktermios *termios,
> struct ktermios *old)
> {
> @@ -1611,12 +1679,17 @@ lpuart32_set_termios(struct uart_port *port,
> struct ktermios *termios,
> lpuart32_write(old_ctrl & ~(UARTCTRL_TE | UARTCTRL_RE),
> sport->port.membase + 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(bd, sport->port.membase + UARTBAUD);
> + if (of_device_is_compatible(port->dev->of_node, "fsl,imx7ulp-lpuart")) {
Shouldn't we be consequent here and also use a flag in the soc data
instead of of_device_is_compatible...?
Btw, instead of using 3 bools, I would prefer using a single flags like
your patchset is proposing for the GPIO driver, what do you think?
--
Stefan
> + lpuart32_serial_setbrg(sport, baud);
> + } else {
> + 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(bd, sport->port.membase + UARTBAUD);
> + }
> +
> lpuart32_write(modem, sport->port.membase + UARTMODIR);
> lpuart32_write(ctrl, sport->port.membase + UARTCTRL);
> /* restore control register */
--
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