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Message-ID: <CALszF6BWuUYRh+3rWnSQLApkAHA5dQXw=6x6D_evRtb+5B_ukA@mail.gmail.com>
Date: Tue, 17 Mar 2015 18:32:24 +0100
From: Maxime Coquelin <mcoquelin.stm32@...il.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>,
Andreas Färber <afaerber@...e.de>,
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Subject: Re: [PATCH v3 10/15] serial: stm32-usart: Add STM32 USART Driver
2015-03-13 15:19 GMT+01:00 Andy Shevchenko <andy.shevchenko@...il.com>:
> On Thu, Mar 12, 2015 at 11:55 PM, Maxime Coquelin
> <mcoquelin.stm32@...il.com> wrote:
>> From: Maxime Coquelin <mcoquelin.stm32@...il.com>
>>
>> This drivers adds support to the STM32 USART controller, which is a
>> standard serial driver.
>
> My comment below.
>
>>
>> Signed-off-by: Maxime Coquelin <mcoquelin.stm32@...il.com>
>> ---
>> drivers/tty/serial/Kconfig | 17 +
>> drivers/tty/serial/Makefile | 1 +
>> drivers/tty/serial/stm32-usart.c | 695 +++++++++++++++++++++++++++++++++++++++
>> include/uapi/linux/serial_core.h | 3 +
>> 4 files changed, 716 insertions(+)
>> create mode 100644 drivers/tty/serial/stm32-usart.c
>>
>> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
>> index d2501f0..880cb4f 100644
>> --- a/drivers/tty/serial/Kconfig
>> +++ b/drivers/tty/serial/Kconfig
>> @@ -1611,6 +1611,23 @@ config SERIAL_SPRD_CONSOLE
>> with "earlycon" on the kernel command line. The console is
>> enabled when early_param is processed.
>>
>> +config SERIAL_STM32
>> + tristate "STMicroelectronics STM32 serial port support"
>> + select SERIAL_CORE
>> + depends on ARM || COMPILE_TEST
>> + help
>> + This driver is for the on-chip Serial Controller on
>> + STMicroelectronics STM32 MCUs.
>> + USART supports Rx & Tx functionality.
>> + It support all industry standard baud rates.
>> +
>> + If unsure, say N.
>> +
>> +config SERIAL_STM32_CONSOLE
>> + bool "Support for console on STM32"
>> + depends on SERIAL_STM32=y
>> + select SERIAL_CORE_CONSOLE
>> +
>> endmenu
>>
>> config SERIAL_MCTRL_GPIO
>> diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
>> index 599be4b..67c5023 100644
>> --- a/drivers/tty/serial/Makefile
>> +++ b/drivers/tty/serial/Makefile
>> @@ -95,6 +95,7 @@ obj-$(CONFIG_SERIAL_FSL_LPUART) += fsl_lpuart.o
>> obj-$(CONFIG_SERIAL_CONEXANT_DIGICOLOR) += digicolor-usart.o
>> obj-$(CONFIG_SERIAL_MEN_Z135) += men_z135_uart.o
>> obj-$(CONFIG_SERIAL_SPRD) += sprd_serial.o
>> +obj-$(CONFIG_SERIAL_STM32) += stm32-usart.o
>>
>> # GPIOLIB helpers for modem control lines
>> obj-$(CONFIG_SERIAL_MCTRL_GPIO) += serial_mctrl_gpio.o
>> diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
>> new file mode 100644
>> index 0000000..61bb065
>> --- /dev/null
>> +++ b/drivers/tty/serial/stm32-usart.c
>> @@ -0,0 +1,695 @@
<snip>
>> +
>> +static void stm32_set_termios(struct uart_port *port, struct ktermios *termios,
>> + struct ktermios *old)
>> +{
>> + unsigned int baud;
>> + u32 usardiv, mantissa, fraction;
>> + tcflag_t cflag;
>> + u32 cr1, cr2, cr3;
>> + unsigned long flags;
>> +
>> + baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk / 16);
>> + cflag = termios->c_cflag;
>> +
>> + spin_lock_irqsave(&port->lock, flags);
>> +
>> + /* Stop serial port and reset value */
>> + writel_relaxed(0, port->membase + USART_CR1);
>> +
>> + cr1 = USART_CR1_TE | USART_CR1_RE | USART_CR1_UE | USART_CR1_RXNEIE;
>> +
>> + if (cflag & CSTOPB)
>> + cr2 = USART_CR2_STOP_2B;
>> +
>> + if (cflag & PARENB) {
>> + cr1 |= USART_CR1_PCE;
>> + if ((cflag & CSIZE) == CS8)
>> + cr1 |= USART_CR1_M;
>> + }
>> +
>> + if (cflag & PARODD)
>> + cr1 |= USART_CR1_PS;
>> +
>> + if (cflag & CRTSCTS)
>> + cr3 = USART_CR3_RTSE | USART_CR3_CTSE;
>> +
>> + usardiv = (port->uartclk * 25) / (baud * 4);
>> + mantissa = (usardiv / 100) << USART_BRR_DIV_M_SHIFT;
>> + fraction = DIV_ROUND_CLOSEST((usardiv % 100) * 16, 100);
>> + if (fraction & ~USART_BRR_DIV_F_MASK) {
>> + fraction = 0;
>> + mantissa += (1 << USART_BRR_DIV_M_SHIFT);
>> + }
>
> So, it's a fractional divider. right? Could it be then fractional
> divider clock in this first place (see
> drivers/clk/clk-fractional-divider.c)?
>
I'm not sure it makes sense to represent this baudrate divider within
the UART IP as a clock.
What would be the gain?
Kind regards,
Maxime
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