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Using only 4 DMA periods for UART RX is very few if we have a high frequency of small transfers - like in our case using Bluetooth with many small packets via UART - causing many dma transfers but in each only filling a fraction of a single buffer. Such a case may lead to the situation that DMA RX transfer is triggered but no free buffer is available. When this happens dma channel ist stopped - with the patch "dmaengine: imx-sdma: fix dma freezes" temporarily only - with the possible consequences that: with disabled hw flow control: If enough data is incoming on UART port the RX FIFO runs over and characters will be lost. What then happens depends on upper layer. with enabled hw flow control: If enough data is incoming on UART port the RX FIFO reaches a level where CTS is deasserted and remote device sending the data stops. If it fails to stop timely the i.MX' RX FIFO may run over and data get lost. Otherwise it's internal TX buffer may getting filled to a point where it runs over and data is again lost. It depends on the remote device how this case is handled and if it is recoverable. Obviously we want to avoid having no free buffers available. So we decrease the size of the buffers and increase their number and the total buffer size. Signed-off-by: Philipp Puschmann <philipp.puschmann@emlix.com> Reviewed-by: Lucas Stach <l.stach@pengutronix.de> Link: https://lore.kernel.org/r/20190923135916.1212-1-philipp.puschmann@emlix.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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| .. | ||
| hvc | ||
| ipwireless | ||
| serdev | ||
| serial | ||
| vt | ||
| amiserial.c | ||
| cyclades.c | ||
| ehv_bytechan.c | ||
| goldfish.c | ||
| isicom.c | ||
| Kconfig | ||
| Makefile | ||
| mips_ejtag_fdc.c | ||
| moxa.c | ||
| moxa.h | ||
| mxser.c | ||
| mxser.h | ||
| n_gsm.c | ||
| n_hdlc.c | ||
| n_null.c | ||
| n_r3964.c | ||
| n_tracerouter.c | ||
| n_tracesink.c | ||
| n_tracesink.h | ||
| n_tty.c | ||
| nozomi.c | ||
| pty.c | ||
| rocket_int.h | ||
| rocket.c | ||
| rocket.h | ||
| synclink_gt.c | ||
| synclink.c | ||
| synclinkmp.c | ||
| sysrq.c | ||
| tty_audit.c | ||
| tty_baudrate.c | ||
| tty_buffer.c | ||
| tty_io.c | ||
| tty_ioctl.c | ||
| tty_jobctrl.c | ||
| tty_ldisc.c | ||
| tty_ldsem.c | ||
| tty_mutex.c | ||
| tty_port.c | ||
| ttynull.c | ||
| vcc.c | ||