Russell King wrote:
> On Fri, Sep 09, 2005 at 04:49:27AM +0200, Mathias Adam wrote:
> > + if (up->port.type == PORT_16C950) {
> > + unsigned int baud_base = port->uartclk/16;
>
> baud_base appears unused.
you're right, it's not necessary anymore. (New patch below)
> > + if (baud <= port->uartclk/16)
> > + serial_icr_write(up, UART_TCR, 0);
> > + else if (baud <= port->uartclk/8) {
> > + serial_icr_write(up, UART_TCR, 0x8);
> > + } else if (baud <= port->uartclk/4) {
> > + serial_icr_write(up, UART_TCR, 0x4);
> > + } else
> > + serial_icr_write(up, UART_TCR, 0);
>
> baud can't be larger than port->uartclk/4 since you limited it above.
Those lines come from 2.4.29's drivers/char/serial.c (>= line 1686). I
left in the last "else" to have some fallback if uart_get_baud_rate()
would change its behaviour to something else (i.e. does allow baud to
be larger than max_baud). However this would lead to an incorrect baud
rate to be set anyway (as the maximum baud rate of 16C950 is uartclk/4),
so one could simply set the "/4" mode for everything larger than uartclk/8.
Btw, if you look at lines 1700-1701 of original 2.6.13's 8250.c:
baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16);
quot = serial8250_get_divisor(port, baud);
baud is limited to uartclk/16 here, but serial8250_get_divisor() tests
it for being uartclk/4 or uartclk/8...
I'm afraid that max_baud thing has to become somewhat more general, or
do I miss something?
Hmm and I don't get the point in the calculation of "quot" - is that
formula correct in every case? I'll look into that a little bit now.
Mathias Adam
PS: I'm now subscribed to the list.
--- linux-2.6.13-org/drivers/serial/8250.c 2005-08-29 01:41:01.000000000 +0200
+++ linux-2.6.13/drivers/serial/8250.c 2005-09-09 15:33:23.000000000 +0200
@@ -1665,7 +1665,7 @@
struct uart_8250_port *up = (struct uart_8250_port *)port;
unsigned char cval, fcr = 0;
unsigned long flags;
- unsigned int baud, quot;
+ unsigned int baud, quot, max_baud;
switch (termios->c_cflag & CSIZE) {
case CS5:
@@ -1697,9 +1697,25 @@
/*
* Ask the core to calculate the divisor for us.
*/
- baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16);
+ max_baud = (up->port.type == PORT_16C950 ? port->uartclk/4 : port->uartclk/16);
+ baud = uart_get_baud_rate(port, termios, old, 0, max_baud);
quot = serial8250_get_divisor(port, baud);
+ /*
+ * 16C950 supports additional prescaler ratios between 1:16 and 1:4
+ * thus increasing max baud rate to uartclk/4. The following was taken
+ * from kernel 2.4 by Mathias Adam <[email protected]> to make the Socket
+ * Bluetooth CF Card work under 2.6.13.
+ */
+ if (up->port.type == PORT_16C950) {
+ if (baud <= port->uartclk/16)
+ serial_icr_write(up, UART_TCR, 0);
+ else if (baud <= port->uartclk/8) {
+ serial_icr_write(up, UART_TCR, 0x8);
+ } else
+ serial_icr_write(up, UART_TCR, 0x4);
+ }
+
/*
* Oxford Semi 952 rev B workaround
*/
-
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