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serial: imx: always restart DMA if more data is available 

Simplify the DMA restart logic to always queue up the next transfer
immediately if there is at least one more byte available in the FIFO,
so that the transfer will finish in a limited time.

This way the driver stops to rely on zero length transfers to signal
transfers ends. Those will go away when the idle detect DMA requests
are disabled.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Jiada Wang <jiada_wang@mentor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
hifive-unleashed-5.1
Lucas Stach 2015-09-04 17:52:39 +02:00 committed by Greg Kroah-Hartman
parent 86a04ba642
commit 976b39cd5b
1 changed files with 13 additions and 16 deletions
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29
drivers/tty/serial/imx.c
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@ -927,23 +927,20 @@ static void dma_rx_callback(void *data)
sport->port.icount.buf_overrun++;
}
tty_flip_buffer_push(port);
start_rx_dma(sport);
} else if (readl(sport->port.membase + USR2) & USR2_RDR) {
/*
* start rx_dma directly once data in RXFIFO, more efficient
* than before:
* 1. call imx_rx_dma_done to stop dma if no data received
* 2. wait next RDR interrupt to start dma transfer.
*/
start_rx_dma(sport);
} else {
/*
* stop dma to prevent too many IDLE event trigged if no data
* in RXFIFO
*/
imx_rx_dma_done(sport);
}
/*
* Restart RX DMA directly if more data is available in order to skip
* the roundtrip through the IRQ handler. If there is some data already
* in the FIFO, DMA needs to be restarted soon anyways.
*
* Otherwise stop the DMA and reactivate FIFO IRQs to restart DMA once
* data starts to arrive again.
*/
if (readl(sport->port.membase + USR2) & USR2_RDR)
start_rx_dma(sport);
else
imx_rx_dma_done(sport);
}
static int start_rx_dma(struct imx_port *sport)