XON/XOFF are used for software flow-control on serial lines. XON and XOFF appear as characters within the stream but should be processed as soon as possible. The characters received by the UART drivers are in intermediate buffers until TTY receives them. In the case where the TTY is not read from, the characters may get stuck into those intermediate buffers until user-space reads from the TTY. Among the characters stuck in the buffers, can also be those XON/XOFF flow control characters. A stuck flow-control character is not very useful. This patch series addresses the issue by checking if TTY is slow to process characters, that is, eats less than the given amount. If TTY is slow, a lookahead is invoked for the characters that remain in the intermediate buffer(s). Then at a later time, receive_buf needs to ensure the flow-control actions are not retaken when those same characters get pushed to TTY. The necessary guards for that are added by the first patch of the series. This patch series fixes an issue but I'm not able to pinpoint to a specific commit id to provide a Fixes tag. Ilpo Järvinen (2): tty: Add lookahead param to receive_buf tty: Implement lookahead to process XON/XOFF timely drivers/accessibility/speakup/spk_ttyio.c | 2 +- drivers/bluetooth/hci_ldisc.c | 2 +- drivers/char/pcmcia/synclink_cs.c | 2 +- drivers/input/serio/serport.c | 2 +- drivers/isdn/capi/capi.c | 2 +- drivers/misc/ti-st/st_core.c | 2 +- drivers/net/caif/caif_serial.c | 4 +- drivers/net/can/slcan.c | 2 +- drivers/net/hamradio/6pack.c | 2 +- drivers/net/hamradio/mkiss.c | 2 +- drivers/net/mctp/mctp-serial.c | 2 +- drivers/net/ppp/ppp_async.c | 2 +- drivers/net/ppp/ppp_synctty.c | 2 +- drivers/net/slip/slip.c | 2 +- drivers/tty/n_gsm.c | 2 +- drivers/tty/n_hdlc.c | 2 +- drivers/tty/n_null.c | 2 +- drivers/tty/n_tty.c | 85 ++++++++++++++++------- drivers/tty/serdev/serdev-ttyport.c | 3 +- drivers/tty/synclink_gt.c | 2 +- drivers/tty/tty_buffer.c | 68 ++++++++++++++---- drivers/tty/tty_io.c | 2 +- drivers/tty/tty_port.c | 27 ++++++- drivers/tty/vt/selection.c | 2 +- include/linux/tty_buffer.h | 1 + include/linux/tty_flip.h | 2 +- include/linux/tty_ldisc.h | 6 +- include/linux/tty_port.h | 3 +- net/nfc/nci/uart.c | 2 +- sound/soc/codecs/cx20442.c | 2 +- sound/soc/ti/ams-delta.c | 2 +- 31 files changed, 174 insertions(+), 69 deletions(-) -- 2.30.2
