From 08a0c6dff91c965e39905cf200d22db989203ccb Mon Sep 17 00:00:00 2001 From: Lukas Wunner Date: Sun, 2 Jan 2022 18:42:44 +0100 Subject: serial: pl010: Drop CR register reset on set_termios 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 Signed-off-by: Lukas Wunner Link: https://lore.kernel.org/r/fcaff16e5b1abb4cc3da5a2879ac13f278b99ed0.1641128728.git.lukas@wunner.de Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/amba-pl010.c | 3 --- 1 file changed, 3 deletions(-) (limited to 'drivers/tty') diff --git a/drivers/tty/serial/amba-pl010.c b/drivers/tty/serial/amba-pl010.c index e744b953ca34..47654073123d 100644 --- a/drivers/tty/serial/amba-pl010.c +++ b/drivers/tty/serial/amba-pl010.c @@ -446,14 +446,11 @@ 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); -- cgit