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USB: pl2303: refactor baud-rate divisor handling

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Refactor baud-rate divisor handling.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Johan Hovold 2013-12-29 19:23:13 +01:00 • committed by Greg Kroah-Hartman
parent 871996ede1
commit c82c6d45a2
1 changed files with 25 additions and 16 deletions
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41
drivers/usb/serial/pl2303.c
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@ -339,6 +339,28 @@ static speed_t pl2303_get_supported_baud_rate(speed_t baud)
return baud; return baud;
} }
static speed_t pl2303_encode_baud_rate_divisor(unsigned char buf[4],
speed_t baud)
{
unsigned int tmp;
/*
* Apparently the formula is:
* baudrate = 12M * 32 / (2^buf[1]) / buf[0]
*/
tmp = 12000000 * 32 / baud;
buf[3] = 0x80;
buf[2] = 0;
buf[1] = (tmp >= 256);
while (tmp >= 256) {
tmp >>= 2;
buf[1] <<= 1;
}
buf[0] = tmp;
return baud;
}
static void pl2303_encode_baud_rate(struct tty_struct *tty, static void pl2303_encode_baud_rate(struct tty_struct *tty,
struct usb_serial_port *port, struct usb_serial_port *port,
u8 buf[4]) u8 buf[4])
@ -362,23 +384,10 @@ static void pl2303_encode_baud_rate(struct tty_struct *tty,
*/ */
baud = pl2303_get_supported_baud_rate(baud); baud = pl2303_get_supported_baud_rate(baud);
if (baud <= 115200) { if (baud <= 115200)
put_unaligned_le32(baud, buf); put_unaligned_le32(baud, buf);
} else { else
/* baud = pl2303_encode_baud_rate_divisor(buf, baud);
* Apparently the formula for higher speeds is:
* baudrate = 12M * 32 / (2^buf[1]) / buf[0]
*/
unsigned tmp = 12000000 * 32 / baud;
buf[3] = 0x80;
buf[2] = 0;
buf[1] = (tmp >= 256);
while (tmp >= 256) {
tmp >>= 2;
buf[1] <<= 1;
}
buf[0] = tmp;
}
/* Save resulting baud rate */ /* Save resulting baud rate */
tty_encode_baud_rate(tty, baud, baud); tty_encode_baud_rate(tty, baud, baud);