2 From: Petr Vandrovec <vandrove@vc.cvut.cz>
4 Patch below adds support for using different prescaler than 16 for 16c950
5 chips. This is needed for using Fujitsu-Siemens Connect2Air compact-flash
6 card, which comes (apparently) with 806kHz clocks, and so you have to
7 program prescaler for division by 7, and DLAB to 1, to get 115200Bd.
9 To get card properly running you also have to add lines below to
10 /etc/pcmcia/serial.opts so kernel knows that base speed is not 115200 but
11 50400 (50400 * 16 = 806400; 806400 / 7 = 115200). As I've found no code
12 specifying baud_rate in serial_cs, I assume that specifying it in
13 serial.opts is right way to do this type of things.
15 Patch also fixes problem that for UPF_MAGIC_MULTIPLIER maximum possible
16 baud rate passed to uart code was uartclk / 16 while correct value for
17 these devices (and for 16c950) is uartclk / 4.
19 Patch also fixes problem that for UPF_MAGIC_MULTIPLIER devices with
20 baud_rate 19200 or 9600 spd_cust did not work correctly. Not that such
21 devices exist, but we should not ignore spd_cust, user probably knows why
22 he asked for spd_cust.
26 case "$MANFID-$FUNCID-$PRODID_1-$PRODID_2-$PRODID_3-$PRODID_4" in
27 '0279,950b-2-GPRS Modem---')
28 SERIAL_OPTS="baud_base 50400"
32 Cc: David Woodhouse <dwmw2@infradead.org>
33 Signed-off-by: Andrew Morton <akpm@osdl.org>
36 drivers/serial/8250.c | 82 +++++++++++++++++++++++++++++++++++++++-----------
37 1 files changed, 64 insertions(+), 18 deletions(-)
39 diff -puN drivers/serial/8250.c~serial-add-support-for-non-standard-xtals-to-16c950-driver drivers/serial/8250.c
40 --- devel/drivers/serial/8250.c~serial-add-support-for-non-standard-xtals-to-16c950-driver 2005-09-12 03:34:57.000000000 -0700
41 +++ devel-akpm/drivers/serial/8250.c 2005-09-12 03:34:57.000000000 -0700
42 @@ -1653,24 +1653,58 @@ static void serial8250_shutdown(struct u
43 serial_unlink_irq_chain(up);
46 -static unsigned int serial8250_get_divisor(struct uart_port *port, unsigned int baud)
47 +static unsigned int serial8250_get_divisor(struct uart_port *port, unsigned int baud,
48 + unsigned int *prescaler)
53 - * Handle magic divisors for baud rates above baud_base on
54 - * SMSC SuperIO chips.
56 + * Use special handling only if user did not supply its own divider.
57 + * spd_cust is defined in terms of baud_base, so always use default
58 + * prescaler when spd_cust is requested.
60 - if ((port->flags & UPF_MAGIC_MULTIPLIER) &&
61 - baud == (port->uartclk/4))
63 - else if ((port->flags & UPF_MAGIC_MULTIPLIER) &&
64 - baud == (port->uartclk/8))
67 - quot = uart_get_divisor(port, baud);
71 + if (baud != 38400 || (port->flags & UPF_SPD_MASK) != UPF_SPD_CUST) {
72 + unsigned int quot = port->uartclk / baud;
75 + * Handle magic divisors for baud rates above baud_base on
76 + * SMSC SuperIO chips.
78 + if (port->flags & UPF_MAGIC_MULTIPLIER) {
81 + } else if (quot == 8) {
85 + if (port->type == PORT_16C950) {
87 + * This computes TCR value (4 to 16), not CPR value (which can
88 + * be between 1.000 and 31.875) - chip I have uses XTAL of
89 + * 806400Hz, and so a division by 7 is required to get 115200Bd.
90 + * I'm leaving CPR disabled for now, until someone will
91 + * hit even more exotic XTAL (it is needed to get 500kbps
92 + * or 1000kbps from 18.432MHz XTAL, but I have no device
93 + * which would benefit from doing that).
95 + * If we can use divide by 16, use it. Otherwise look for
96 + * better prescaler, from 15 to 4. If quotient cannot
97 + * be divided by any integer value between 4 and 15, use 4.
102 + for (div = 15; div > 4; div--) {
103 + if (quot % div == 0) {
112 + return uart_get_divisor(port, baud);
116 @@ -1680,7 +1714,7 @@ serial8250_set_termios(struct uart_port
117 struct uart_8250_port *up = (struct uart_8250_port *)port;
118 unsigned char cval, fcr = 0;
120 - unsigned int baud, quot;
121 + unsigned int baud, quot, prescaler;
123 switch (termios->c_cflag & CSIZE) {
125 @@ -1712,8 +1746,13 @@ serial8250_set_termios(struct uart_port
127 * Ask the core to calculate the divisor for us.
129 - baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16);
130 - quot = serial8250_get_divisor(port, baud);
132 + if (port->type == PORT_16C950 || (port->flags & UPF_MAGIC_MULTIPLIER)) {
133 + baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/4);
135 + baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16);
137 + quot = serial8250_get_divisor(port, baud, &prescaler);
140 * Oxford Semi 952 rev B workaround
141 @@ -1817,6 +1856,13 @@ serial8250_set_termios(struct uart_port
142 serial_outp(up, UART_DLM, quot >> 8); /* MS of divisor */
145 + * Program prescaler for 16C950 chips.
147 + if (up->port.type == PORT_16C950) {
148 + serial_icr_write(up, UART_TCR, prescaler == 16 ? 0 : prescaler);
152 * LCR DLAB must be set to enable 64-byte FIFO mode. If the FCR
153 * is written without DLAB set, this mode will be disabled.