From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Agner Subject: Re: [PATCH V2 6/6] tty: serial: lpuart: add a more accurate baud rate calculation method Date: Mon, 15 May 2017 10:06:41 -0700 Message-ID: <73a70b856adf28b34c793f03c4db43a9@agner.ch> References: <1494834539-17523-1-git-send-email-aisheng.dong@nxp.com> <1494834539-17523-7-git-send-email-aisheng.dong@nxp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <1494834539-17523-7-git-send-email-aisheng.dong@nxp.com> Sender: linux-kernel-owner@vger.kernel.org To: Dong Aisheng Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, gregkh@linuxfoundation.org, jslaby@suse.com, fugang.duan@nxp.com, dongas86@gmail.com, Mingkai.Hu@nxp.com, yangbo.lu@nxp.com List-Id: linux-serial@vger.kernel.org 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 > Cc: Jiri Slaby > Cc: Stefan Agner > Cc: Mingkai Hu > Cc: Yangbo Lu > Acked-by: Fugang Duan > Signed-off-by: Dong Aisheng > --- > 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 */