Commit d02b006b authored by Johan Hovold's avatar Johan Hovold Committed by Greg Kroah-Hartman
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Revert "serial: 8250: Fix reporting real baudrate value in c_ospeed field" 



This reverts commit 32262e2e.

The commit in question claims to determine the inverse of
serial8250_get_divisor() but failed to notice that some drivers override
the default implementation using a get_divisor() callback.

This means that the computed line-speed values can be completely wrong
and results in regular TCSETS requests failing (the incorrect values
would also be passed to any overridden set_divisor() callback).

Similarly, it also failed to honour the old (deprecated) ASYNC_SPD_FLAGS
and would break applications relying on those when re-encoding the
actual line speed.

There are also at least two quirks, UART_BUG_QUOT and an OMAP1510
workaround, which were happily ignored and that are now broken.

Finally, even if the offending commit were to be implemented correctly,
this is a new feature and not something which should be backported to
stable.

Cc: Pali Rohár <pali@kernel.org>
Fixes: 32262e2e ("serial: 8250: Fix reporting real baudrate value in c_ospeed field")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: default avatarJohan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20211007133146.28949-1-johan@kernel.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 32262e2e

drivers/tty/serial/8250/8250_port.c

+0 −17
Original line number Diff line number Diff line
@@ -2584,19 +2584,6 @@ 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)

{
@@ -2727,14 +2714,11 @@ 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);
@@ -2766,7 +2750,6 @@ 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