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Message-ID: <alpine.LFD.2.20.1704021149550.1847@knanqh.ubzr>
Date: Sun, 2 Apr 2017 11:55:34 -0400 (EDT)
From: Nicolas Pitre <nicolas.pitre@...aro.org>
To: Andy Shevchenko <andy.shevchenko@...il.com>
cc: Alan Cox <alan@...ux.intel.com>, Rob Herring <robh@...nel.org>,
Peter Hurley <peter@...leysoftware.com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jslaby@...e.com>,
"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 0/5] minitty: a minimal TTY layer alternative for
embedded systems
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@...aro.org> 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
>
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