On Tue, Apr 26, 2022 at 05:49:32PM +0300, Ilpo Järvinen wrote: > For this v4, I dropped Gilles' Tested-by as I made rather major > modifications to the patch series so I don't want to claim he has > tested this version (earlier versions are known to fix his problem and > this one should too). > > 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. > > This patch series fixes an issue but I'm not able to pinpoint to a > specific commit id to provide a Fixes tag. The last patch of the series > is not needed for minimal fix (and has a small chance of regression > too), thus that patch shouldn't be sent to stable. > > v1 -> v2: > - Add flow ctrl char funcs in separate change & rework logic a bit. > I believe it's now cleaner than it would have been with the > suggestions during v1 review, please recheck. > - Renamed n_tty_lookahead_special to n_tty_lookahead_flow_ctrl > - Fixed logic for START_CHAR == STOP_CHAR case > - Use unsigned int for lookahead_count in receive_buf call chain > - Use consistent types in lookahead call chain > - Improved indentation & line splits for function params > - Corrected tty_ldisc.h comments documenting tty_ldisc_ops > - Tweaked comment format > > v2 -> v3: > - Split preparatory patch moving/rearranging code to two > - Fix closing path giving change for ... || xx to execute > instead of skipping the flow-control char > - Use the same flow-control char function on closing path > (just a cleanup, non-fix as last patch, a small change of > regression exists) > > v3 -> v4: > - Rework lookahead_count, it is now kept internal to n_tty ldisc rather > than passed around through the whole callchain > - Dropped Gilles' Tested-by due to major changes > - Improve comments & changelogs > > Ilpo Järvinen (3): > tty: Rework receive flow control char logic > tty: Implement lookahead to process XON/XOFF timely > tty: Use flow-control char function on closing path > > drivers/tty/n_tty.c | 107 ++++++++++++++++++++++++++++--------- > drivers/tty/tty_buffer.c | 59 ++++++++++++++++---- > drivers/tty/tty_port.c | 21 ++++++++ > include/linux/tty_buffer.h | 1 + > include/linux/tty_ldisc.h | 13 +++++ > include/linux/tty_port.h | 2 + > 6 files changed, 170 insertions(+), 33 deletions(-) > > -- > 2.30.2 > I took patch 1/3 of this series as it is "obviously correct". I'd like others to review the rest before taking them, and I don't have the bandwidth today to do so, so I'll wait for others before considering them. thanks, greg k-h
