| From 3d7b0ba61d91645616121131b4e604b4b8ba5cbb Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Sun, 8 May 2022 12:41:47 +0206 |
| Subject: serial: meson: acquire port->lock in startup() |
| |
| 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.com |
| 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 6aea0f4a9165..273292f09bf6 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_CLR_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, |
| meson_uart_type(port), port); |
| |
| -- |
| 2.35.1 |
| |