• Cyrille Pitchen's avatar
    tty/serial: at91: fix RTS line management when hardware handshake is enabled · 1cf6e8fc
    Cyrille Pitchen authored
    This patch fixes many bugs in the code dealing with the hardware handshake.
    
    As an example, in atmel_set_termios(), we used to test whether the CRTSCTS
    c_cflag was set. If so, we selected the "Hardware Handshake" mode through the
    Mode Register. However, few lines below the mode was reset to "Normal" (0).
    So there was no way to select the "Hardware Handshake" mode. To fix this issue,
    we moved the CRTSCRTS c_cflag test AFTER the mode has been reset to "Normal".
    
    Also setting the RTSEN and RTSDIS bits in the Control Register has different
    results whether the USART is set in "Normal" or "Hardware Handshake" mode:
    
    1) "Normal" mode
    - the RTSEN bit forces the RTS line to low level, which tells the remote peer
      that we are ready to received new data.
    - the RTSDIS bit forces the RTS line to high level, which tells the remote peer
      to stop sending new data.
    
    2) "Hardware Handshake" mode
    - the RTSEN bit forces the RTS line to high level.
    - the RTSDIS bit lets the hardware control the RTS line.
    
    WARNING:
    when FIFOs are not available or not enabled, the RTS line is controlled by the
    PDC. This is why using the Hardware Handshake mode requires using the PDC
    channel for reception. However the Hardware Handshake mode DOES NOT work with
    DMA controller since it cannot control the RTS line.
    Future designs with FIFOs will introduce a new feature: the RTS line will be
    controlled by the RX FIFO using thresholds. This patch was tested with this new
    design.
    Signed-off-by: default avatarCyrille Pitchen <cyrille.pitchen@atmel.com>
    Acked-by: default avatarNicolas Ferre <nicolas.ferre@atmel.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    1cf6e8fc
atmel_serial.c 68.2 KB