On Wed, May 17, 2017 at 10:35:43AM -0700, Stefan Agner wrote:

On 2017-05-16 20:47, Dong Aisheng wrote:

quoted

On Mon, May 15, 2017 at 10:06:41AM -0700, Stefan Agner wrote:

quoted

On 2017-05-15 00:48, Dong Aisheng wrote:

quoted

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@linuxfoundation.org>
Cc: Jiri Slaby <redacted>
Cc: Stefan Agner <stefan@agner.ch>
Cc: Mingkai Hu <Mingkai.Hu@nxp.com>
Cc: Yangbo Lu <yangbo.lu@nxp.com>
Acked-by: Fugang Duan <redacted>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
---
 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...?

The original purpose is that this is a temporary code and supposed will
be deleted later once LS platforms confirmed the new baud setting API
works for them as well.

That's why i did not make it a property, as i stated in the cover letter.

Ok, I see that is a good reason to not define a new feature property
now... 

But, if you are reasonable sure it should work, I am inclined to say
just enable it for LS1021a so it also really gets tested...

Okay, i'll take this suggestion to get things started.

Thanks

Regards
Dong Aisheng