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serial: 8250: Fix reporting real baudrate value in c_ospeed field

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In most cases it is not possible to set exact baudrate value to hardware.

So fix reporting real baudrate value which was set to hardware via c_ospeed
termios field. It can be retrieved by ioctl(TCGETS2) from userspace.

Real baudrate value is calculated from chosen hardware divisor and base
clock. It is implemented in a new function serial8250_compute_baud_rate()
which is inverse of serial8250_get_divisor() function.

With this change is fixed also UART timeout value (it is updated via
uart_update_timeout() function), which is calculated from the now fixed
baudrate value too.

Cc: stable@vger.kernel.org
Signed-off-by: Pali Rohár <pali@kernel.org>
Link: https://lore.kernel.org/r/20210927093704.19768-1-pali@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Pali Rohár 2021-09-27 11:37:04 +02:00 committed by Greg Kroah-Hartman
parent 027b57170b
commit 32262e2e42
1 changed files with 17 additions and 0 deletions
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17
drivers/tty/serial/8250/8250_port.c
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@ -2584,6 +2584,19 @@ static unsigned int serial8250_get_divisor(struct uart_port *port,
return serial8250_do_get_divisor(port, baud, frac);
}
static unsigned int serial8250_compute_baud_rate(struct uart_port *port,
unsigned int quot)
{
if ((port->flags & UPF_MAGIC_MULTIPLIER) && quot == 0x8001)
return port->uartclk / 4;
else if ((port->flags & UPF_MAGIC_MULTIPLIER) && quot == 0x8002)
return port->uartclk / 8;
else if (port->type == PORT_NPCM)
return DIV_ROUND_CLOSEST(port->uartclk - 2 * (quot + 2), 16 * (quot + 2));
else
return DIV_ROUND_CLOSEST(port->uartclk, 16 * quot);
}
static unsigned char serial8250_compute_lcr(struct uart_8250_port *up,
tcflag_t c_cflag)
{
@ -2714,11 +2727,14 @@ void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk)
baud = serial8250_get_baud_rate(port, termios, NULL);
quot = serial8250_get_divisor(port, baud, &frac);
baud = serial8250_compute_baud_rate(port, quot);
serial8250_rpm_get(up);
spin_lock_irqsave(&port->lock, flags);
uart_update_timeout(port, termios->c_cflag, baud);
if (tty_termios_baud_rate(termios))
tty_termios_encode_baud_rate(termios, baud, baud);
serial8250_set_divisor(port, baud, quot, frac);
serial_port_out(port, UART_LCR, up->lcr);
@ -2750,6 +2766,7 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
baud = serial8250_get_baud_rate(port, termios, old);
quot = serial8250_get_divisor(port, baud, &frac);
baud = serial8250_compute_baud_rate(port, quot);
/*
* Ok, we're now changing the port state. Do it with