On Tue, Mar 17, 2015 at 7:32 PM, Maxime Coquelin
[off-list ref] wrote:

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

quoted

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.

You have it already. I mean it should be fractional divider clock.

stm32port->clk = devm_clk_get(&pdev->dev, NULL);
+
+       if (WARN_ON(IS_ERR(stm32port->clk)))
+               return -EINVAL;
+
+       /* ensure that clk rate is correct by enabling the clk */
+       clk_prepare_enable(stm32port->clk);
+       stm32port->port.uartclk = clk_get_rate(stm32port->clk);

What would be the gain?

Remove custom implementation of the calculations. It will be just one
line to refresh the baud rate. I think we have a lot of duplicates
here and there in the kernel. It would be nice not to bring another
one.

-- 
With Best Regards,
Andy Shevchenko