From: Hugo Villeneuve hvilleneuve@dimonoff.com
When enabling access to the special register set, Receiver time-out and RHR interrupts can happen. In this case, the IRQ handler will try to read from the FIFO thru the RHR register at address 0x00, but address 0x00 is mapped to DLL register, resulting in erroneous FIFO reading.
Call graph example: sc16is7xx_startup(): entry sc16is7xx_ms_proc(): entry sc16is7xx_set_termios(): entry sc16is7xx_set_baud(): DLH/DLL = $009C --> access special register set sc16is7xx_port_irq() entry --> IIR is 0x0C sc16is7xx_handle_rx() entry sc16is7xx_fifo_read(): --> unable to access FIFO (RHR) because it is mapped to DLL (LCR=LCR_CONF_MODE_A) sc16is7xx_set_baud(): exit --> Restore access to general register set
Fix the problem by claiming the efr_lock mutex when accessing the Special register set.
Reworked to fix conflicts when backporting to linux-5.15.y.
Fixes: dfeae619d781 ("serial: sc16is7xx") Cc: stable@vger.kernel.org Signed-off-by: Hugo Villeneuve hvilleneuve@dimonoff.com Link: https://lore.kernel.org/r/20240723125302.1305372-3-hugo@hugovil.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/serial/sc16is7xx.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c index 928c701f0c35a..3b7c238793ef4 100644 --- a/drivers/tty/serial/sc16is7xx.c +++ b/drivers/tty/serial/sc16is7xx.c @@ -537,6 +537,8 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud) prescaler == 1 ? 0 : SC16IS7XX_MCR_CLKSEL_BIT);
/* Open the LCR divisors for configuration */ + mutex_lock(&one->efr_lock); + sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, SC16IS7XX_LCR_CONF_MODE_A);
@@ -549,6 +551,8 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud) /* Put LCR back to the normal mode */ sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
+ mutex_unlock(&one->efr_lock); + return DIV_ROUND_CLOSEST((clk / prescaler) / 16, div); }