Message-ID: <AANLkTinxNlCSBqBggTIlVqyyn4NLy4LbZU8SFAlqPLow@mail.gmail.com>
Date:	Thu, 22 Jul 2010 21:19:25 +0200
From:	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:	Mattia Jona-Lasinio <mattia.jona@...il.com>
Cc:	linux-kernel@...r.kernel.org, Willy Tarreau <w@....eu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Walleij <triad@...lth.se>,
	linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	ivan.kuten@...mwad.com, lcd-linux-users@...ts.sourceforge.net,
	Viktar Palstsiuk <viktar.palstsiuk@...mwad.com>
Subject: Re: Introducing the LCD-Linux project

On Wed, Jul 21, 2010 at 2:57 PM, Mattia Jona-Lasinio
<mattia.jona@...il.com> wrote:
> Hi,
>
> this is to introduce the LCD-Linux project (http://lcd-linux.sourceforge.net/),
> a kernel level implementation of a VT102 terminal emulator, optimized for small
> alphanumeric and graphic displays.
>
> The possibility to connect to the computer small alphanumeric as well as graphic
> displays, has always attracted some interest. These small devices are connected
> to the computer and can be used to display system diagnostics like network
> usage, RAM or disk usage or even to replace the usual monitor. Possible
> applications can be found in embedded systems or clusters. These displays are
> connected to the computer through serial lines, parallel ports and more recently
> through USB connections. Appropriate programs in userspace gather the desired
> information and output it on the display. However for this to work, the
> userspace program has to implement some sort of display management, to determine
> what must be displayed where. This has two major disadvantages. First. Every
> userspace program willing to drive a display must solve the very same problems
> (display scroll and refresh, for instance), resulting in an overall duplication
> of code. Second. Display controllers usually require quite strict timings for
> proper operation and it is not trivial neither efficient to obtain this in
> userspace, whereas it is straightforward in kernel space through the usual delay
> functions. A solution is therefore to provide a sort of minimal terminal
> emulation in kernel space, that can be accessed through the standard character
> device interface. In this way the problem of the display management is reduced
> to some calls to the usual read/write/seek/ioctl routines. At the same time one
> has the possibility to implement handling of escape sequences, thus opening the
> way to standard applications based on the ncurses library.

Someone told me once ago, when I submitted the cfag12864b/ks0108
drivers, to make them use a framebuffer, so we could get a console on
it using a program like con2fb program in an independent manner. It
worked flawlessly and the console was quite usable!

I see that you want to implement something more complex, but maybe
someone/you can make a use of that idea. Check it out : )

>
> LCD-Linux aims to be a complete VT102 terminal emulation in kernel space,
> optimized for small alphanumeric and graphic displays. It consists of two
> distinct pieces of software.
>
> The first piece is the lcd-linux module in itself, implementing a (hopefully)
> complete VT102 terminal with the addition of some custom escape sequences
> specific to the world of small LCD displays. Care has been taken to avoid any
> conflict between standard and custom escape sequences. A major feature of
> lcd-linux is the possibility to define a virtual display geometry larger than
> the physical one, so that one can use a small display as a normal 80x25 monitor
> in an effective way. The layer takes care about display refresh and keeps the
> cursor visible in a smart way. A second feature is the possibility to connect
> more than one display (up to 256 different displays). Each display is assigned a
> different minor number and is addressed individually. The lcd-linux module also
> registers the appropriate major number character device and implements all the
> relevant read/write/seek/ioctl functions allowed on the character device.
> Finally it creates some /proc files for internal inspection, information and
> diagnostics.
>
> The second piece of software is the display driver, implementing all functions
> that are controller specific. Each driver registers itself with the lcd-linux
> layer and behaves like a 'slave' with respect to it. The interface between
> lcd-linux and the display driver is kept as simple as possible and no assumption
> is made by any of the two parts on the implementation of the other part. Ideally
> there will be one module for each controller. At the current stage, the driver
> for the Hitachi HD44780 (and compatibles) controller is fully implemented and
> optimized. Drivers for other controllers can be written in an easy way thanks to
> the standard interface provided by the lcd-linux layer.
>
> The LCD-Linux project has been under development for several years and has now
> reached a stable state. It has been succesfully compiled, tested and used on
> different machines running Linux version 2.2, 2.4 and 2.6. The software can be
> compiled as a module or compiled statically into the kernel. In the latter case,
> the user can pass some parameters at boot time, to configure the display as soon
> as possible during the boot sequence. The project comes with Documentation and
> examples about how to use it.
>
> LCD-Linux is released under the GNU General Public License version 2. The latest
> release is available at the Sourceforge website:
>
> http://lcd-linux.sourceforge.net/
> http://prdownloads.sourceforge.net/lcd-linux/lcd-linux-0.13.9.tar.gz?download
>
> The CVS version still includes some partial support for Linux 2.0 but this
> support is considered obsolete and now abandoned in the official release.
>
> The LCD4Linux (http://ssl.bulix.org/projects/lcd4linux/) project is known to
> support LCD-Linux among the possible connection types.
>
> I would appreciate some comments and feedback on the project. In view of the
> potential applications, future developments and improvements of LCD-Linux, I
> would also like to propose LCD-Linux for inclusion in the Linux kernel mainline.
>
> Thank you for your attention.
>
> With best regards,
>
> Mattia Jona-Lasinio
>
> (LCD-Linux project developer and maintainer)
>
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