On Sun, 2 Apr 2017, Andy Shevchenko wrote: > +Cc people, who have a key roles in all TTY stuff (btw, why you did > miss them? I used what MAINTAINERS and get_maintainer.pl gave me. > why you didn't include people who reacted on your v1 > either?). > I'm pretty sure they are interested in what's going on here. The only one I missed is Ard. Thanks for pulling more people in. > > On Sun, Apr 2, 2017 at 1:21 AM, Nicolas Pitre <nicolas.pitre@xxxxxxxxxx> wrote: > > Many embedded systems don't need the full TTY layer support. Most of the > > time, the TTY layer is only a conduit for outputting debugging messages > > over a serial port. The TTY layer also implements many features that are > > very unlikely to ever be used in such a setup. There is great potential > > for both code and dynamic memory size reduction on small systems. This is > > what this patch series is achieving. > > > > The existing TTY code is quite large and complex. Trying to shrink it > > is risky as the potential for breakage is non negligeable, and its > > interchangeable layers impose a lower limit on the code to implement it. > > Therefore, the approach used here consists in the creation of a parallel > > implementation with the very minimal amount of code collapsed together > > that interfaces with existing UART drivers directly and provides TTY-like > > character devices to user space. When the regular TTY layer is disabled, > > then this minitty alternative layer is proposed by Kconfig. > > > > For more details on the rationale and motivations driving this approach > > please see: https://lkml.org/lkml/2017/3/24/634 > > > > Of course, making it "mini" means there are limitations to what it does: > > > > - This supports serial ports only. No VT's, no PTY's. > > > > - The default n_tty line discipline is hardcoded and no other line > > discipline are supported. > > > > - The line discipline features are not all implemented. Notably, XON/XOFF > > is currently not implemented (although this might not require a lot of > > code to do it if someone were to need it). > > > > - Hung-up state is not implemented. > > > > - No error handling on RX bytes other than counting them. > > > > - Job control is currently not supported (this may change in the future and > > be configurable). > > > > But again, most small embedded systems simply don't need those things. > > > > This can be used on any architecture of course, but here's some numbers > > using a minimal ARM config. > > > > When CONFIG_TTY=y, the following files are linked into the kernel: > > > > text data bss dec hex filename > > 8796 128 0 8924 22dc drivers/tty/n_tty.o > > 11809 276 0 12085 2f35 drivers/tty/serial/fulltty_serial.o > > 1376 0 0 1376 560 drivers/tty/tty_buffer.o > > 13571 172 132 13875 3633 drivers/tty/tty_io.o > > 3072 0 0 3072 c00 drivers/tty/tty_ioctl.o > > 2457 2 120 2579 a13 drivers/tty/tty_ldisc.o > > 1328 0 0 1328 530 drivers/tty/tty_ldsem.o > > 316 0 0 316 13c drivers/tty/tty_mutex.o > > 2516 0 0 2516 9d4 drivers/tty/tty_port.o > > 5241 578 252 46071 b3f7 (TOTALS) > > > > When CONFIG_TTY=n and CONFIG_MINITTY_SERIAL=y, the above files are replaced > > by the following: > > > > text data bss dec hex filename > > 8063 8 64 8135 1fc7 drivers/tty/serial/minitty_serial.o > > > > That's it! And the runtime buffer usage is much less as well. Future plans > > such as removing runtime baudrate handling for those targets with a known > > fixed baudrate will shrink the code even more. > > > > Changes from v1: > > > > - Added an entry to the MAINTAINERS file. > > - Factored out more common core code into serial_lib.c. > > - Implemented a few more TTY callback functions to be compatible with > > more UART drivers. > > > > Overall diffstat: > > > > MAINTAINERS | 8 +- > > drivers/tty/Kconfig | 10 +- > > drivers/tty/Makefile | 3 +- > > drivers/tty/serial/Kconfig | 12 +- > > drivers/tty/serial/Makefile | 7 +- > > .../serial/{serial_core.c => fulltty_serial.c} | 419 +--- > > drivers/tty/serial/minitty_serial.c | 1793 +++++++++++++++++ > > drivers/tty/serial/serial_lib.c | 440 ++++ > > drivers/tty/tty_baudrate.c | 232 +++ > > drivers/tty/tty_io.c | 24 - > > drivers/tty/tty_ioctl.c | 222 -- > > include/linux/console.h | 2 + > > include/linux/serial_core.h | 1 + > > include/linux/tty.h | 7 +- > > include/linux/tty_flip.h | 9 + > > init/main.c | 2 +- > > kernel/printk/printk.c | 24 + > > 17 files changed, 2538 insertions(+), 677 deletions(-) > > > > -- > With Best Regards, > Andy Shevchenko > -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
