1 files changed, 19 insertions, 2 deletions

diff --git a/drivers/mmc/card/sdio_uart.c b/drivers/mmc/card/sdio_uart.c
index 606100212afa..d552de683110 100644
--- a/drivers/mmc/card/sdio_uart.c
+++ b/drivers/mmc/card/sdio_uart.c
@@ -79,6 +79,7 @@ struct sdio_uart_port {
         struct mutex            open_lock;
         struct sdio_func        *func;
         struct mutex            func_lock;
+        struct task_struct      *in_sdio_uart_irq;
         unsigned int            regs_offset;
         struct circ_buf         xmit;
         spinlock_t              write_lock;
@@ -186,14 +187,16 @@ static int sdio_uart_claim_func(struct sdio_uart_port *port)
                 mutex_unlock(&port->func_lock);
                 return -ENODEV;
         }
-        sdio_claim_host(port->func);
+        if (likely(port->in_sdio_uart_irq != current))
+                sdio_claim_host(port->func);
         mutex_unlock(&port->func_lock);
         return 0;
 }
 
 static inline void sdio_uart_release_func(struct sdio_uart_port *port)
 {
-        sdio_release_host(port->func);
+        if (likely(port->in_sdio_uart_irq != current))
+                sdio_release_host(port->func);
 }
 
 static inline unsigned int sdio_in(struct sdio_uart_port *port, int offset)
@@ -511,15 +514,29 @@ static void sdio_uart_irq(struct sdio_func *func)
         struct sdio_uart_port *port = sdio_get_drvdata(func);
         unsigned int iir, lsr;
 
+        /*
+         * In a few places sdio_uart_irq() is called directly instead of
+         * waiting for the actual interrupt to be raised and the SDIO IRQ
+         * thread scheduled in order to reduce latency.  However, some
+         * interaction with the tty core may end up calling us back
+         * (serial echo, flow control, etc.) through those same places
+         * causing undesirable effects.  Let's stop the recursion here.
+         */
+        if (unlikely(port->in_sdio_uart_irq == current))
+                return;
+
         iir = sdio_in(port, UART_IIR);
         if (iir & UART_IIR_NO_INT)
                 return;
+
+        port->in_sdio_uart_irq = current;
         lsr = sdio_in(port, UART_LSR);
         if (lsr & UART_LSR_DR)
                 sdio_uart_receive_chars(port, &lsr);
         sdio_uart_check_modem_status(port);
         if (lsr & UART_LSR_THRE)
                 sdio_uart_transmit_chars(port);
+        port->in_sdio_uart_irq = NULL;
 }
 
 static int sdio_uart_startup(struct sdio_uart_port *port)