From: Lukas Wunner lukas@wunner.de
[ Upstream commit 08a0c6dff91c965e39905cf200d22db989203ccb ]
pl010_set_termios() briefly resets the CR register to zero.
Where does this register write come from?
The PL010 driver's IRQ handler ambauart_int() originally modified the CR register without holding the port spinlock. ambauart_set_termios() also modified that register. To prevent concurrent read-modify-writes by the IRQ handler and to prevent transmission while changing baudrate, ambauart_set_termios() had to disable interrupts. That is achieved by writing zero to the CR register.
However in 2004 the PL010 driver was amended to acquire the port spinlock in the IRQ handler, obviating the need to disable interrupts in ->set_termios(): https://git.kernel.org/history/history/c/157c0342e591
That rendered the CR register write obsolete. Drop it.
Cc: Russell King rmk+kernel@armlinux.org.uk Signed-off-by: Lukas Wunner lukas@wunner.de Link: https://lore.kernel.org/r/fcaff16e5b1abb4cc3da5a2879ac13f278b99ed0.164112872... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/tty/serial/amba-pl010.c | 3 --- 1 file changed, 3 deletions(-)
diff --git a/drivers/tty/serial/amba-pl010.c b/drivers/tty/serial/amba-pl010.c index 9ec4b8d2879f7..0698fbf3b6d61 100644 --- a/drivers/tty/serial/amba-pl010.c +++ b/drivers/tty/serial/amba-pl010.c @@ -465,14 +465,11 @@ pl010_set_termios(struct uart_port *port, struct ktermios *termios, if ((termios->c_cflag & CREAD) == 0) uap->port.ignore_status_mask |= UART_DUMMY_RSR_RX;
- /* first, disable everything */ old_cr = readb(uap->port.membase + UART010_CR) & ~UART010_CR_MSIE;
if (UART_ENABLE_MS(port, termios->c_cflag)) old_cr |= UART010_CR_MSIE;
- writel(0, uap->port.membase + UART010_CR); - /* Set baud rate */ quot -= 1; writel((quot & 0xf00) >> 8, uap->port.membase + UART010_LCRM);