[PATCH] serial: stm32: optimize spin lock usage

[dillon . minfei]

From: dillon min <dillon.min...@gmail.com>

To avoid potential deadlock in spin_lock usage, change to use
spin_lock_irqsave(), spin_unlock_irqrestore() in process(thread_fn) context.
spin_lock(), spin_unlock() under handler context.

remove unused local_irq_save/restore call.

Signed-off-by: dillon min <dillon.min...@gmail.com>
---
Was verified on stm32f469-disco board. need more test on stm32mp platform.

 drivers/tty/serial/stm32-usart.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index b3675cf25a69..c4c859b34367 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -214,7 +214,7 @@ static void stm32_usart_receive_chars(struct uart_port 
*port, bool threaded)
        struct tty_port *tport = &port->state->port;
        struct stm32_port *stm32_port = to_stm32_port(port);
        const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
-       unsigned long c;
+       unsigned long c, flags;
        u32 sr;
        char flag;
 
@@ -276,9 +276,17 @@ static void stm32_usart_receive_chars(struct uart_port 
*port, bool threaded)
                uart_insert_char(port, sr, USART_SR_ORE, c, flag);
        }
 
-       spin_unlock(&port->lock);
+       if (threaded)
+               spin_unlock_irqrestore(&port->lock, flags);
+       else
+               spin_unlock(&port->lock);
+
        tty_flip_buffer_push(tport);
-       spin_lock(&port->lock);
+
+       if (threaded)
+               spin_lock_irqsave(&port->lock, flags);
+       else
+               spin_lock(&port->lock);
 }
 
 static void stm32_usart_tx_dma_complete(void *arg)
@@ -489,13 +497,14 @@ static irqreturn_t stm32_usart_threaded_interrupt(int 
irq, void *ptr)
 {
        struct uart_port *port = ptr;
        struct stm32_port *stm32_port = to_stm32_port(port);
+       unsigned long flags;
 
-       spin_lock(&port->lock);
+       spin_lock_irqsave(&port->lock, flags);
 
        if (stm32_port->rx_ch)
                stm32_usart_receive_chars(port, true);
 
-       spin_unlock(&port->lock);
+       spin_unlock_irqrestore(&port->lock, flags);
 
        return IRQ_HANDLED;
 }
@@ -1354,13 +1363,12 @@ static void stm32_usart_console_write(struct console 
*co, const char *s,
        u32 old_cr1, new_cr1;
        int locked = 1;
 
-       local_irq_save(flags);
        if (port->sysrq)
                locked = 0;
        else if (oops_in_progress)
-               locked = spin_trylock(&port->lock);
+               locked = spin_trylock_irqsave(&port->lock, flags);
        else
-               spin_lock(&port->lock);
+               spin_lock_irqsave(&port->lock, flags);
 
        /* Save and disable interrupts, enable the transmitter */
        old_cr1 = readl_relaxed(port->membase + ofs->cr1);
@@ -1374,8 +1382,7 @@ static void stm32_usart_console_write(struct console *co, 
const char *s,
        writel_relaxed(old_cr1, port->membase + ofs->cr1);
 
        if (locked)
-               spin_unlock(&port->lock);
-       local_irq_restore(flags);
+               spin_unlock_irqrestore(&port->lock, flags);
 }
 
 static int stm32_usart_console_setup(struct console *co, char *options)
-- 
2.7.4