From: John Ogness john.ogness@linutronix.de
[ Upstream commit 589f892ac8ef244e47c5a00ffd8605daa1eaef8e ]
The uart_ops startup() callback is called without interrupts disabled and without port->lock locked, relatively late during the boot process (from the call path of console_on_rootfs()). If the device is a console, it was already previously registered and could be actively printing messages.
Since the startup() callback is reading/writing registers used by the console write() callback (AML_UART_CONTROL), its access must be synchronized using the port->lock. Currently it is not.
The startup() callback is the only function that explicitly enables interrupts. Without the synchronization, it is possible that interrupts become accidentally permanently disabled.
CPU0 CPU1 meson_serial_console_write meson_uart_startup -------------------------- ------------------ spin_lock(port->lock) val = readl(AML_UART_CONTROL) uart_console_write() writel(INT_EN, AML_UART_CONTROL) writel(val, AML_UART_CONTROL) spin_unlock(port->lock)
Add port->lock synchronization to meson_uart_startup() to avoid racing with meson_serial_console_write().
Also add detailed comments to meson_uart_reset() explaining why it is *not* using port->lock synchronization.
Link: https://lore.kernel.org/lkml/2a82eae7-a256-f70c-fd82-4e510750906e@samsung.co... Fixes: ff7693d079e5 ("ARM: meson: serial: add MesonX SoC on-chip uart driver") Reported-by: Marek Szyprowski m.szyprowski@samsung.com Tested-by: Marek Szyprowski m.szyprowski@samsung.com Reviewed-by: Petr Mladek pmladek@suse.com Reviewed-by: Jiri Slaby jirislaby@kernel.org Acked-by: Neil Armstrong narmstrong@baylibre.com Signed-off-by: John Ogness john.ogness@linutronix.de Link: https://lore.kernel.org/r/20220508103547.626355-1-john.ogness@linutronix.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/tty/serial/meson_uart.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c index 45e00d928253..54a6b488bc8c 100644 --- a/drivers/tty/serial/meson_uart.c +++ b/drivers/tty/serial/meson_uart.c @@ -253,6 +253,14 @@ static const char *meson_uart_type(struct uart_port *port) return (port->type == PORT_MESON) ? "meson_uart" : NULL; }
+/* + * This function is called only from probe() using a temporary io mapping + * in order to perform a reset before setting up the device. Since the + * temporarily mapped region was successfully requested, there can be no + * console on this port at this time. Hence it is not necessary for this + * function to acquire the port->lock. (Since there is no console on this + * port at this time, the port->lock is not initialized yet.) + */ static void meson_uart_reset(struct uart_port *port) { u32 val; @@ -267,9 +275,12 @@ static void meson_uart_reset(struct uart_port *port)
static int meson_uart_startup(struct uart_port *port) { + unsigned long flags; u32 val; int ret = 0;
+ spin_lock_irqsave(&port->lock, flags); + val = readl(port->membase + AML_UART_CONTROL); val |= AML_UART_CLEAR_ERR; writel(val, port->membase + AML_UART_CONTROL); @@ -285,6 +296,8 @@ static int meson_uart_startup(struct uart_port *port) val = (AML_UART_RECV_IRQ(1) | AML_UART_XMIT_IRQ(port->fifosize / 2)); writel(val, port->membase + AML_UART_MISC);
+ spin_unlock_irqrestore(&port->lock, flags); + ret = request_irq(port->irq, meson_uart_interrupt, 0, port->name, port);