linux-kernel - console font limits

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Message-ID: <787b0d920704302109r352e6653wc71a0638cbfbdcce@mail.gmail.com>
Date:	Tue, 1 May 2007 00:09:46 -0400
From:	"Albert Cahalan" <acahalan@...il.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>, aeb@....nl,
	hpa@...or.com
Subject: console font limits

I'm having problems with a font I just created. It's a rather big one,
intended for a framebuffer console in UTF-8 mode. The strace program
reports that /bin/setfont fails on a KDFONTOP ioctl with EINVAL.
In reading the kernel code, I find this:

vt.c:static int con_font_set(struct vc_data *vc, struct console_font_op *op)
vt.c-{
vt.c-   struct console_font font;
vt.c-   int rc = -EINVAL;
vt.c-   int size;
vt.c-
vt.c-   if (vc->vc_mode != KD_TEXT)
vt.c-           return -EINVAL;
vt.c-   if (!op->data)
vt.c-           return -EINVAL;
vt.c-   if (op->charcount > 512)
vt.c-           return -EINVAL;

Ouch. Why is the old VGA limit being applied to the framebuffer console?
Could this just get removed? I dearly hope we aren't still storing the
framebuffer data as two bytes per character+attribute pair.

I nearly hit the 32-pixel height limit as well, yet another relic from
the VGA hardware. I also nearly hit the 64 KB font size limit.

Currently I'm doing a 15x30 font with 870 glyphs to represent 978
different Unicode code points. This is for a 200 DPI display with
an anti-aliasing filter, so fonts need to be big. I'm considering 15x36
so that I'll have more room for double-accented letters, but clearly
the kernel would block that too.

BTW, the PSF font format documentation seems to suggest that
there is a way to make the kernel handle combining accents:
http://www.win.tue.nl/~aeb/linux/kbd/font-formats-1.html
Does anybody know if that really works? I could sure use that.
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