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Commit 8d6e4b42 authored by Jay Dolan's avatar Jay Dolan Committed by Greg Kroah-Hartman
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serial: 8250_pci: rewrite pericom_do_set_divisor() 



commit bb1201d4b38ec67bd9a871cf86b0cc10f28b15b5 upstream.

Have pericom_do_set_divisor() use the uartclk instead of a hard coded
value to work with different speed crystals. Tested with 14.7456 and 24
MHz crystals.

Have pericom_do_set_divisor() always calculate the divisor rather than
call serial8250_do_set_divisor() for rates below baud_base.

Do not write registers or call serial8250_do_set_divisor() if valid
divisors could not be found.

Fixes: 6bf4e42f ("serial: 8250: Add support for higher baud rates to Pericom chips")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: default avatarJay Dolan <jay.dolan@accesio.com>
Signed-off-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211122120604.3909-3-andriy.shevchenko@linux.intel.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 181cf762

drivers/tty/serial/8250/8250_pci.c

+17 −13
Original line number Diff line number Diff line
@@ -1351,29 +1351,33 @@ pericom_do_set_divisor(struct uart_port *port, unsigned int baud, 
{

	int scr;

	int lcr;

	int actual_baud;

	int tolerance;



	for (scr = 5 ; scr <= 15 ; scr++) {

		actual_baud = 921600 * 16 / scr;

		tolerance = actual_baud / 50;

	for (scr = 16; scr > 4; scr--) {

		unsigned int maxrate = port->uartclk / scr;

		unsigned int divisor = max(maxrate / baud, 1U);

		int delta = maxrate / divisor - baud;



		if ((baud < actual_baud + tolerance) &&

			(baud > actual_baud - tolerance)) {

		if (baud > maxrate + baud / 50)

			continue;



		if (delta > baud / 50)

			divisor++;



		if (divisor > 0xffff)

			continue;



		/* Update delta due to possible divisor change */

		delta = maxrate / divisor - baud;

		if (abs(delta) < baud / 50) {

			lcr = serial_port_in(port, UART_LCR);

			serial_port_out(port, UART_LCR, lcr | 0x80);



			serial_port_out(port, UART_DLL, 1);

			serial_port_out(port, UART_DLM, 0);

			serial_port_out(port, UART_DLL, divisor & 0xff);

			serial_port_out(port, UART_DLM, divisor >> 8 & 0xff);

			serial_port_out(port, 2, 16 - scr);

			serial_port_out(port, UART_LCR, lcr);

			return;

		} else if (baud > actual_baud) {

			break;

		}

	}

	serial8250_do_set_divisor(port, baud, quot, quot_frac);

}

static int pci_pericom_setup(struct serial_private *priv,

		  const struct pciserial_board *board,