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serial: 8250_pci: rewrite pericom_do_set_divisor() 

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: 6bf4e42f1d ("serial: 8250: Add support for higher baud rates to Pericom chips")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Jay Dolan <jay.dolan@accesio.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211122120604.3909-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jay Dolan 2021-11-22 14:06:04 +02:00 committed by Greg Kroah-Hartman
parent c525c5d243
commit bb1201d4b3
1 changed files with 17 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
drivers/tty/serial/8250/8250_pci.c
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@ -1324,29 +1324,33 @@ 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,