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    SubjectRe: [PATCH 4/5] tty: serial: 8250 core: add runtime pm
    * Peter Hurley | 2014-07-17 11:31:59 [-0400]:

    >On 07/16/2014 12:06 PM, Felipe Balbi wrote:
    >>On Wed, Jul 16, 2014 at 05:54:56PM +0200, Sebastian Andrzej Siewior wrote:
    >>>On 07/16/2014 05:16 PM, Felipe Balbi wrote:
    >
    >>>>I wonder if you should get_sync() on start_tx() and only
    >>>>put_autosuspend() at stop_tx(). I guess the outcome would be
    >>>>largely the same, no ?
    >>>
    >>>I just opened minicom on ttyS0 and gave a try. start_tx() was invoked
    >>>each time I pressed a key (sent a character). I haven't seen stop_tx()
    >>>even after after I closed minicom. I guess stop_tx() is invoked if you
    >>>switch half-duplex communication.
    >>
    >>that's bad, I expected stop to be called also after each character.
    >
    >The 8250 core auto-stops tx when the tx ring buffer is empty (except
    >in the case of dma, where stopping tx isn't necessary).

    This is correct. So this is what I have now for the non-dma case:

    diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
    index 2e4a93b..480a1c0 100644
    --- a/drivers/tty/serial/8250/8250_core.c
    +++ b/drivers/tty/serial/8250/8250_core.c
    @@ -1283,6 +1283,9 @@ static inline void __stop_tx(struct uart_8250_port *p)
    if (p->ier & UART_IER_THRI) {
    p->ier &= ~UART_IER_THRI;
    serial_out(p, UART_IER, p->ier);
    +
    + pm_runtime_mark_last_busy(p->port.dev);
    + pm_runtime_put_autosuspend(p->port.dev);
    }
    }

    @@ -1310,12 +1313,12 @@ static void serial8250_start_tx(struct uart_port *port)
    struct uart_8250_port *up =
    container_of(port, struct uart_8250_port, port);

    - pm_runtime_get_sync(port->dev);
    if (up->dma && !serial8250_tx_dma(up)) {
    goto out;
    } else if (!(up->ier & UART_IER_THRI)) {
    up->ier |= UART_IER_THRI;
    + pm_runtime_get_sync(port->dev);
    serial_port_out(port, UART_IER, up->ier);

    if (up->bugs & UART_BUG_TXEN) {
    unsigned char lsr;
    @@ -1500,9 +1503,10 @@ void serial8250_tx_chars(struct uart_8250_port *up)
    uart_write_wakeup(port);

    DEBUG_INTR("THRE...");
    -
    +#if 0
    if (uart_circ_empty(xmit))
    __stop_tx(up);
    +#endif
    }
    EXPORT_SYMBOL_GPL(serial8250_tx_chars);

    and now I need to come up with something that is not if (port != omap)
    for that #if 0 block. The code disables the TX FIFO empty interrupt once
    the transfer is complete. I want to call __stop_tx() once the tx fifo is
    empty.
    Felipe, Would a check for dev->power.use_autosuspend be the right thing
    to do?
    >Regards,
    >Peter Hurley

    Sebastian


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