On Wed, Sep 10, 2014 at 09:30:08PM +0200, Sebastian Andrzej Siewior wrote:
> There is nothing to do for RPM in the RX path. If the HW goes off then it
> won't assert the DMA line and the transfer won't happen. So we hope that
> the HW does not go off for RX to work (DMA or PIO makes no difference
> here).
>
> For TX the situation is slightly different. RPM is enabled on
> start_tx(). We can't disable RPM on DMA complete callback because there
> is still data in the FIFO which is being sent. We have to wait until
> the FIFO is empty before we disable it.
> For this to happen we fake a TX sent error and enable THRI. Once the
> FIFO is empty we receive an interrupt and since the TTY-buffer is still
> empty we "put RPM" via __stop_tx(). Should it been filed then in the
> start_tx() path we should program the DMA transfer and remove the error
> flag and the THRI bit.
That last sentence starts out a bit messy.
>
> Reviewed-by: Tony Lindgren <tony@xxxxxxxxxxx>
> Tested-by: Tony Lindgren <tony@xxxxxxxxxxx>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
> drivers/tty/serial/8250/8250_dma.c | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
> index 898a6781d0b3..e8850219b150 100644
> --- a/drivers/tty/serial/8250/8250_dma.c
> +++ b/drivers/tty/serial/8250/8250_dma.c
> @@ -21,6 +21,7 @@ static void __dma_tx_complete(void *param)
> struct uart_8250_dma *dma = p->dma;
> struct circ_buf *xmit = &p->port.state->xmit;
> unsigned long flags;
> + bool en_thri = false;
>
> dma_sync_single_for_cpu(dma->txchan->device->dev, dma->tx_addr,
> UART_XMIT_SIZE, DMA_TO_DEVICE);
> @@ -40,11 +41,16 @@ static void __dma_tx_complete(void *param)
> int ret;
>
> ret = serial8250_tx_dma(p);
> - if (ret) {
> - dma->tx_err = 1;
> - p->ier |= UART_IER_THRI;
> - serial_port_out(&p->port, UART_IER, p->ier);
> - }
> + if (ret)
> + en_thri = true;
> +
> + } else if (p->capabilities & UART_CAP_RPM)
> + en_thri = true;
> +
> + if (en_thri) {
> + dma->tx_err = 1;
> + p->ier |= UART_IER_THRI;
> + serial_port_out(&p->port, UART_IER, p->ier);
> }
>
> spin_unlock_irqrestore(&p->port.lock, flags);
> --
> 2.1.0
>
>
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