Little patch for sc16is7xx.c

[Michel Vos <mhlvos@xxxxxxxxx>]

Hi, I am working on a board with a nxp sc16is740 and am using the
driver for this. I noticed that when closing a connection the driver
would query the tx level repeatedly and this was caused by this
procedure:

static unsigned int sc16is7xx_tx_empty(struct uart_port *port)
{
        unsigned int lvl, lsr;

        lvl = sc16is7xx_port_read(port, SC16IS7XX_TXLVL_REG);
        lsr = sc16is7xx_port_read(port, SC16IS7XX_LSR_REG);

        return ((lsr & SC16IS7XX_LSR_THRE_BIT) && !lvl) ? TIOCSER_TEMT : 0;
}

The lvl variable seems to contain the number of bytes in the FIFO but
in reality it contains the number of free places in the FIFO. So the
fix I want to propose is this:

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index df9a384..0e59860 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -699,7 +699,7 @@ static unsigned int sc16is7xx_tx_empty(struct
uart_port *port)
 {
        unsigned int lvl, lsr;

-       lvl = sc16is7xx_port_read(port, SC16IS7XX_TXLVL_REG);
+       lvl = sc16is7xx_port_read(port, SC16IS7XX_TXLVL_REG) -
SC16IS7XX_FIFO_SIZE;
        lsr = sc16is7xx_port_read(port, SC16IS7XX_LSR_REG);

        return ((lsr & SC16IS7XX_LSR_THRE_BIT) && !lvl) ? TIOCSER_TEMT : 0;

Regards
Michel Vos
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