Hello,

Ok, have implemented the test_and_clear_bit.

On Tuesday 22 February 2011, Subhasish Ghosh wrote:

quoted

@@ -122,13 +122,10 @@ static void omapl_pru_tx_chars(struct 

omapl_pru_suart
*soft_uart, u32 uart_no)
        if (!(suart_get_duplex(soft_uart, uart_no) & ePRU_SUART_HALF_TX))
                return;

-       if (down_trylock(&soft_uart->port_sem[uart_no]))
-               return;
-
        if (uart_circ_empty(xmit) ||
                        uart_tx_stopped(&soft_uart->port[uart_no])) {
                pruss_suart_stop_tx(&soft_uart->port[uart_no]);
-               up(&soft_uart->port_sem[uart_no]);
+               soft_uart->tx_empty[uart_no] = true;
                return;
        }

@@ -259,7 +256,6 @@ static irqreturn_t pruss_suart_interrupt(s32 irq, 

void
*dev_id)
                        pru_intr_clr_isrstatus(dev, uart_num, 
PRU_TX_INTR);
                        pru_softuart_clr_tx_status(dev, 
&soft_uart->suart_hdl
                                                 [port->line]);
-                       up(&soft_uart->port_sem[port->line]);
                        omapl_pru_tx_chars(soft_uart, port->line);
                }
        } while (txrx_flag & (PRU_RX_INTR | PRU_TX_INTR));

@@ -294,7 +290,10 @@ static void pruss_suart_start_tx(struct uart_port

*port)

        suart_intr_setmask(dev, 
soft_uart->suart_hdl[port->line].uart_num,
                           PRU_TX_INTR, CHN_TXRX_IE_MASK_CMPLT);
-       omapl_pru_tx_chars(soft_uart, port->line);
+       if (soft_uart->tx_empty[port->line] == true) {
+               soft_uart->tx_empty[port->line] = false;
+               omapl_pru_tx_chars(soft_uart, port->line);
+       }
 }

This looks racy, and I think you at least need to take the spinlock in
pruss_suart_start_tx(), but I don't fully understand the intention of the
code.

I guess you could also use a bitmask for tx_empty and use 
test_and_clear_bit()
on that to guarantee atomicity.

Arnd