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Date: Mon, 17 Jan 2022 21:40:01 -0500 From: Sasha Levin <sashal@...nel.org> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org Cc: Lukas Wunner <lukas@...ner.de>, Russell King <rmk+kernel@...linux.org.uk>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Sasha Levin <sashal@...nel.org>, linux@...linux.org.uk, jirislaby@...nel.org, linux-serial@...r.kernel.org Subject: [PATCH AUTOSEL 5.10 110/116] serial: pl010: Drop CR register reset on set_termios From: Lukas Wunner <lukas@...ner.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@...linux.org.uk> Signed-off-by: Lukas Wunner <lukas@...ner.de> Link: https://lore.kernel.org/r/fcaff16e5b1abb4cc3da5a2879ac13f278b99ed0.1641128728.git.lukas@wunner.de Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Signed-off-by: Sasha Levin <sashal@...nel.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 3284f34e9dfe1..75d61e038a775 100644 --- a/drivers/tty/serial/amba-pl010.c +++ b/drivers/tty/serial/amba-pl010.c @@ -448,14 +448,11 @@ 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); -- 2.34.1
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