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    SubjectRe: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx
    * Peter Hurley | 2014-09-23 13:03:51 [-0400]:

    >readline() does this; it 'saves' the caller's termios, sets termios
    >for non-canonical reads, reads one char, and 'restores' the caller's
    >termios.

    interresting, thanks. I guess I would need to opimize this a little so
    the baudrate isn't going to 0 and back to the requested baudrate.

    >The tty core calls the driver's wait_until_sent() method before changing
    >the termios (if TCSADRAIN is used for tcsetattr(), which I think for readline()
    >it does).

    The interresting difference is that when I take the yocto RFS and chroot
    into from Debian then I don't this problem. Not sure if this is really
    readline or something else…

    >But DMA is cheating if the UART driver's tx_empty() method is saying the
    >transmitter is empty while TX DMA is still running.
    This shouldn't be the case. But I will check this once I able to.
    After TX-DMA is done, "xmit->tail" is updated and port.icount.tx is
    incremented. At this time the TX FIFO is still full (up to 64 bytes) and
    I set UART_IER_THRI to wait until TX FIFO is empty so I can disable
    runtime-pm. Therefore I would assume LSR does not say BOTH_EMPTY until
    the FIFO is empty.

    >Regards,
    >Peter Hurley

    Sebastian
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