Commit 5d85045f authored by Johan Hovold's avatar Johan Hovold Committed by Greg Kroah-Hartman
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USB: pl2303: use direct baud-rate encoding when possible 



Use direct baud-rate encoding rather than divisors for supported baud
rates.

This restores the way baud rates were set prior to commit 8d48fdf6
("USB: PL2303: correctly handle baudrates above 115200") which added
divisor encoding, but also switched to the new encoding method for all
baudrates above 115200.

As noted by Frank Schäfer <fschaefer.oss@googlemail.com>, baud rate 500k
was later errounously added to the supported baud-rate table although
it can only be set using divisors.

Note that the current implementation could easily be extended to support
arbitrary non-standard baud rates using divisors (e.g. by falling back
to divisors when the table lookup fails).

Cc: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: default avatarJohan Hovold <jhovold@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 20b4c787

drivers/usb/serial/pl2303.c

+13 −8
Original line number Diff line number Diff line
@@ -312,14 +312,15 @@ static int pl2303_set_control_lines(struct usb_serial_port *port, u8 value) 
}



/*

 * Returns the nearest supported baud rate.

 * Returns the nearest supported baud rate that can be set directly without

 * using divisors.

 */

static speed_t pl2303_get_supported_baud_rate(speed_t baud)

{

	static const speed_t baud_sup[] = {

		75, 150, 300, 600, 1200, 1800, 2400, 3600, 4800, 7200, 9600,

		14400, 19200, 28800, 38400, 57600, 115200, 230400, 460800,

		500000, 614400, 921600, 1228800, 2457600, 3000000, 6000000

		614400, 921600, 1228800, 2457600, 3000000, 6000000

	};



	unsigned i;
@@ -379,6 +380,7 @@ static void pl2303_encode_baud_rate(struct tty_struct *tty, 
{

	struct usb_serial *serial = port->serial;

	struct pl2303_serial_private *spriv = usb_get_serial_data(serial);

	speed_t	baud_sup;

	speed_t baud;



	baud = tty_get_baud_rate(tty);
@@ -388,14 +390,17 @@ static void pl2303_encode_baud_rate(struct tty_struct *tty, 


	if (spriv->type->max_baud_rate)

		baud = min_t(speed_t, baud, spriv->type->max_baud_rate);

	/*

	 * Set baud rate to nearest supported value.

	 *

	 * NOTE: Baud rate 500k can only be set using divisors.

	 */

	baud_sup = pl2303_get_supported_baud_rate(baud);



	/* Set baud rate to nearest supported value. */

	baud = pl2303_get_supported_baud_rate(baud);



	if (baud <= 115200)

		baud = pl2303_encode_baud_rate_direct(buf, baud);

	else

	if (baud == 500000)

		baud = pl2303_encode_baud_rate_divisor(buf, baud);

	else

		baud = pl2303_encode_baud_rate_direct(buf, baud_sup);



	/* Save resulting baud rate */

	tty_encode_baud_rate(tty, baud, baud);

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