ARM: 6158/2: PL011 baudrate extension for ST-Ericssons derivative

Implementation of the ST-Ericsson baudrate extension in the PL011
block. In this modified variant it is possible to change the
sampling factor from 16 to 8, and thanks to this we can get higher
baudrates while still using the same peripheral clock.

Also replace the simple division to determine the baud divisor
with DIV_ROUND_CLOSEST() rather than a simple integer division.

Cc: Alessandro Rubini <rubini@unipv.it>
Cc: Jerzy Kasenberg <jerzy.kasenberg@tieto.com>
Signed-off-by: Marcin Mielczarczyk <marcin.mielczarczyk@tieto.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

2 files changed, 26 insertions, 2 deletions

diff --git a/drivers/serial/amba-pl011.c b/drivers/serial/amba-pl011.c
index 5644cf2385bb..f67e09da6d33 100644
--- a/drivers/serial/amba-pl011.c
+++ b/drivers/serial/amba-pl011.c
@@ -74,6 +74,7 @@ struct uart_amba_port {
         unsigned int            ifls;           /* vendor-specific */
         unsigned int            lcrh_tx;        /* vendor-specific */
         unsigned int            lcrh_rx;        /* vendor-specific */
+        bool                    oversampling;   /* vendor-specific */
         bool                    autorts;
 };
 
@@ -83,6 +84,7 @@ struct vendor_data {
         unsigned int            fifosize;
         unsigned int            lcrh_tx;
         unsigned int            lcrh_rx;
+        bool                    oversampling;
 };
 
 static struct vendor_data vendor_arm = {
@@ -90,6 +92,7 @@ static struct vendor_data vendor_arm = {
         .fifosize               = 16,
         .lcrh_tx                = UART011_LCRH,
         .lcrh_rx                = UART011_LCRH,
+        .oversampling           = false,
 };
 
 static struct vendor_data vendor_st = {
@@ -97,6 +100,7 @@ static struct vendor_data vendor_st = {
         .fifosize               = 64,
         .lcrh_tx                = ST_UART011_LCRH_TX,
         .lcrh_rx                = ST_UART011_LCRH_RX,
+        .oversampling           = true,
 };
 
 static void pl011_stop_tx(struct uart_port *port)
@@ -499,8 +503,13 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
         /*
          * Ask the core to calculate the divisor for us.
          */
-        baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16);
-        quot = port->uartclk * 4 / baud;
+        baud = uart_get_baud_rate(port, termios, old, 0,
+                                  port->uartclk/(uap->oversampling ? 8 : 16));
+
+        if (baud > port->uartclk/16)
+                quot = DIV_ROUND_CLOSEST(port->uartclk * 8, baud);
+        else
+                quot = DIV_ROUND_CLOSEST(port->uartclk * 4, baud);
 
         switch (termios->c_cflag & CSIZE) {
         case CS5:
@@ -579,6 +588,13 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
                 uap->autorts = false;
         }
 
+        if (uap->oversampling) {
+                if (baud > port->uartclk/16)
+                        old_cr |= ST_UART011_CR_OVSFACT;
+                else
+                        old_cr &= ~ST_UART011_CR_OVSFACT;
+        }
+
         /* Set baud rate */
         writew(quot & 0x3f, port->membase + UART011_FBRD);
         writew(quot >> 6, port->membase + UART011_IBRD);
@@ -744,6 +760,12 @@ pl011_console_get_options(struct uart_amba_port *uap, int *baud,
                 fbrd = readw(uap->port.membase + UART011_FBRD);
 
                 *baud = uap->port.uartclk * 4 / (64 * ibrd + fbrd);
+
+                if (uap->oversampling) {
+                        if (readw(uap->port.membase + UART011_CR)
+                                  & ST_UART011_CR_OVSFACT)
+                                *baud *= 2;
+                }
         }
 }
 
@@ -839,6 +861,7 @@ static int pl011_probe(struct amba_device *dev, struct amba_id *id)
         uap->ifls = vendor->ifls;
         uap->lcrh_rx = vendor->lcrh_rx;
         uap->lcrh_tx = vendor->lcrh_tx;
+        uap->oversampling = vendor->oversampling;
         uap->port.dev = &dev->dev;
         uap->port.mapbase = dev->res.start;
         uap->port.membase = base;
diff --git a/include/linux/amba/serial.h b/include/linux/amba/serial.h
index 93c96a66c518..e1b634b635f2 100644
--- a/include/linux/amba/serial.h
+++ b/include/linux/amba/serial.h
@@ -86,6 +86,7 @@
 #define UART010_CR_TIE          0x0020
 #define UART010_CR_RIE          0x0010
 #define UART010_CR_MSIE         0x0008
+#define ST_UART011_CR_OVSFACT   0x0008  /* Oversampling factor */
 #define UART01x_CR_IIRLP        0x0004  /* SIR low power mode */
 #define UART01x_CR_SIREN        0x0002  /* SIR enable */
 #define UART01x_CR_UARTEN       0x0001  /* UART enable */