This is a note to let you know that I've just added the patch titled

serial: 8250_pci: rewrite pericom_do_set_divisor()

to my tty git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git in the tty-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From bb1201d4b38ec67bd9a871cf86b0cc10f28b15b5 Mon Sep 17 00:00:00 2001

From: Jay Dolan jay.dolan@accesio.com Date: Mon, 22 Nov 2021 14:06:04 +0200 Subject: 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: 6bf4e42f1d19 ("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.inte... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/serial/8250/8250_pci.c | 30 +++++++++++++++++------------- 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c index b793d848aeb6..60f8fffdfd77 100644 --- a/drivers/tty/serial/8250/8250_pci.c +++ b/drivers/tty/serial/8250/8250_pci.c @@ -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,