2015-03-13 15:19 GMT+01:00 Andy Shevchenko [off-list ref]:

On Thu, Mar 12, 2015 at 11:55 PM, Maxime Coquelin
[off-list ref] wrote:

quoted

From: Maxime Coquelin <mcoquelin.stm32@gmail.com>

This drivers adds support to the STM32 USART controller, which is a
standard serial driver.

My comment below.

quoted

Signed-off-by: Maxime Coquelin <mcoquelin.stm32@gmail.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>

quoted

+
+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