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serial: 8250_dma: don't bother DMA with small transfers

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If we would like to send amount of data less than FIFO size we better would do
this via PIO mode. Otherwise the overhead could be significant.

Signed-off-by: Andy Shevchenko <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Andy Shevchenko authored and Greg Kroah-Hartman committed 2015-02-02 10:11:26 -08:00
1 parent a39d1da11b
commit 9119fba0cf
1 file changed
+4
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drivers/tty/serial/8250/8250_dma.c
+4
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@@ -80,6 +80,10 @@ int serial8250_tx_dma(struct uart_8250_port *p)
return 0;
dma->tx_size = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
if (dma->tx_size < p->port.fifosize) {
ret = -EINVAL;
goto err;
}
desc = dmaengine_prep_slave_single(dma->txchan,
dma->tx_addr + xmit->tail,