[PATCH] fix for using >16 pixel wide font in fb console

[PATCH] fix for using >16 pixel wide font in fb console

[Jani Jaakkola]

[ Please, CC any replies to me, I am not a regular kernel hacker ]

I wrote a small tool to convert fonts understood by freetype to linux
console fonts, since I wanted to use larger fonts than the ones shipped
with kbd package on my console. This exposed (at least) two bugs in fb
console driver.

The first one was that fbcon_set_font() used one byte padding for fonts
having width 16 <= width < 24, which was wrong since the pieces of code
actually using the font did not use any padding. This is fixed in the
included patch and also fbcon_set_font() is made a little cleaner. After
the patch the following font is not garbled in fb console:
http://www.cs.helsinki.fi/u/jjaakkol/psf/bitstream_vera_sans_mono_roman.16x30.psf

The other bug is that fonts having height == 32 crash the kernel. I have
no fix for this (at least not yet), but it can be reproduced with font:
http://www.cs.helsinki.fi/u/jjaakkol/psf/bitstream_vera_sans_mono_roman.17x32.psf

The tool (unfinished and probably broken) and some other fonts are
available from http://www.cs.helsinki.fi/u/jjaakkol/psf/

Included patch is against vanilla 2.6.9 kernel.

- Jani

--- linux-2.6.9/drivers/video/console/fbcon.c	Tue Oct 19 00:54:39 2004
+++ linux-2.6.9-csl/drivers/video/console/fbcon.c	Mon Nov  8 01:32:38 2004
@@ -77,7 +77,7 @@
 #include <linux/smp.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
-
+#include <linux/crc32.h> /* For counting font checksums */
 #include <asm/irq.h>
 #include <asm/system.h>
 #include <asm/uaccess.h>
@@ -2352,6 +2352,12 @@
  *  User asked to set font; we are guaranteed that
  *	a) width and height are in range 1..32
  *	b) charcount does not exceed 512
+ *  but lets not assume that, since someone might someday want to use larger
+ *  fonts. And charcount of 512 is small for unicode support.
+ * 
+ *  However, user space gives the font in 32 rows , regardless of 
+ *  actual font height. So a new API is needed if support for larger fonts
+ *  is ever implemented.
  */
 
 static int fbcon_set_font(struct vc_data *vc, struct console_font *font, unsigned flags)
@@ -2359,20 +2365,17 @@
 	unsigned charcount = font->charcount;
 	int w = font->width;
 	int h = font->height;
-	int size = h;
-	int i, k;
-	u8 *new_data, *data = font->data, *p;
+	int size;
+	int i, csum;
+	u8 *new_data, *data = font->data;
+	int pitch = (font->width+7) >> 3;
 
+	/* Is there a reason why fbconsole couldn't handle any charcount >256?
+	 * If not this check should be changed to charcount < 256 */
 	if (charcount != 256 && charcount != 512)
 		return -EINVAL;
 
-	if (w > 8) {
-		if (w <= 16)
-			size *= 2;
-		else
-			size *= 4;
-	}
-	size *= charcount;
+	size = h * pitch * charcount;
 
 	new_data = kmalloc(FONT_EXTRA_WORDS * sizeof(int) + size, GFP_USER);
 
@@ -2383,55 +2386,22 @@
 	FNTSIZE(new_data) = size;
 	FNTCHARCNT(new_data) = charcount;
 	REFCOUNT(new_data) = 0;	/* usage counter */
-	p = new_data;
-	if (w <= 8) {
-		for (i = 0; i < charcount; i++) {
-			memcpy(p, data, h);
-			data += 32;
-			p += h;
-		}
-	} else if (w <= 16) {
-		h *= 2;
-		for (i = 0; i < charcount; i++) {
-			memcpy(p, data, h);
-			data += 64;
-			p += h;
-		}
-	} else if (w <= 24) {
-		for (i = 0; i < charcount; i++) {
-			int j;
-			for (j = 0; j < h; j++) {
-				memcpy(p, data, 3);
-				p[3] = 0;
-				data += 3;
-				p += sizeof(u32);
-			}
-			data += 3 * (32 - h);
-		}
-	} else {
-		h *= 4;
-		for (i = 0; i < charcount; i++) {
-			memcpy(p, data, h);
-			data += 128;
-			p += h;
-		}
+	for (i=0; i< charcount; i++) {
+		memcpy(new_data + i*h*pitch, data +  i*32*pitch, h*pitch);
 	}
-	/* we can do it in u32 chunks because of charcount is 256 or 512, so
-	   font length must be multiple of 256, at least. And 256 is multiple
-	   of 4 */
-	k = 0;
-	while (p > new_data) {
-		p = (u8 *)((u32 *)p - 1);
-		k += *(u32 *) p;
-	}
-	FNTSUM(new_data) = k;
+
+	/* Since linux has a nice crc32 function use it for counting font
+	 * checksums. */
+	csum = crc32(0, new_data, size);
+
+	FNTSUM(new_data) = csum;
 	/* Check if the same font is on some other console already */
 	for (i = 0; i < MAX_NR_CONSOLES; i++) {
 		struct vc_data *tmp = vc_cons[i].d;
 		
 		if (fb_display[i].userfont &&
 		    fb_display[i].fontdata &&
-		    FNTSUM(fb_display[i].fontdata) == k &&
+		    FNTSUM(fb_display[i].fontdata) == csum &&
 		    FNTSIZE(fb_display[i].fontdata) == size &&
 		    tmp->vc_font.width == w &&
 		    !memcmp(fb_display[i].fontdata, new_data, size)) {


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Re: [PATCH] fix for using >16 pixel wide font in fb console

[Antonino A. Daplas]

On Monday 08 November 2004 08:17, Jani Jaakkola wrote:
> [ Please, CC any replies to me, I am not a regular kernel hacker ]
>
> I wrote a small tool to convert fonts understood by freetype to linux
> console fonts, since I wanted to use larger fonts than the ones shipped
> with kbd package on my console. This exposed (at least) two bugs in fb
> console driver.
>
> The first one was that fbcon_set_font() used one byte padding for fonts
> having width 16 <= width < 24, which was wrong since the pieces of code
> actually using the font did not use any padding. This is fixed in the
> included patch and also fbcon_set_font() is made a little cleaner. After
> the patch the following font is not garbled in fb console:
> http://www.cs.helsinki.fi/u/jjaakkol/psf/bitstream_vera_sans_mono_roman.16x
>30.psf
>

Nice, I just checked it on vesafb and rivafb and it works.

> The other bug is that fonts having height == 32 crash the kernel. I have
> no fix for this (at least not yet), but it can be reproduced with font:
> http://www.cs.helsinki.fi/u/jjaakkol/psf/bitstream_vera_sans_mono_roman.17x
>32.psf

I think I know where the problem is. The src bitmap is statically allocated
at 64 bytes, enough for a 16x32 font, previously the maximum font dimension
allowed.  Dynamically allocating it based on the font dimension fixes the
problem (patch attached), at least for drivers with no hardware cursor
implementation, such as vesafb.  (I tested it on rivafb, but I get cursor
corruption, probably a driver problem. Also nvidia's maximum cursor
dimension is 32x32, so it's probably hitting a corner case bug).

>
> +	/* Is there a reason why fbconsole couldn't handle any charcount >256?
> +	 * If not this check should be changed to charcount < 256 */

This is because the console was based on VGA in which each character is
described in 16 bits.  The upper byte is for the attributes and the lower byte
is for the character.  Sometimes, one can use bit 8, giving 9-bits allowing
for 512 bytes of character count.

Tony

PS: Diff is against 2.6.10-rc1-mm3





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Re: [PATCH] fix for using >16 pixel wide font in fb console

[Antonino A. Daplas]

On Monday 08 November 2004 18:16, Antonino A. Daplas wrote:
> On Monday 08 November 2004 08:17, Jani Jaakkola wrote:

> PS: Diff is against 2.6.10-rc1-mm3

And I forgot to attach the patch :-)

Tony

diff -Nru a/drivers/video/softcursor.c b/drivers/video/softcursor.c
--- a/drivers/video/softcursor.c	2004-10-27 16:28:36 +08:00
+++ b/drivers/video/softcursor.c	2004-11-08 18:10:58 +08:00
@@ -28,16 +28,17 @@
 	if (info->state != FBINFO_STATE_RUNNING)
 		return 0;
 
-	src = kmalloc(64 + sizeof(struct fb_image), GFP_ATOMIC);
+	s_pitch = (cursor->image.width + 7) >> 3;
+	dsize = s_pitch * cursor->image.height;
 
+	src = kmalloc(dsize + sizeof(struct fb_image), GFP_ATOMIC);
 	if (!src)
 		return -ENOMEM;
 
-	image = (struct fb_image *) (src + 64);
+	image = (struct fb_image *) (src + dsize);
 	*image = cursor->image;
-	s_pitch = (image->width + 7) >> 3;
-	dsize = s_pitch * image->height;
 	d_pitch = (s_pitch + scan_align) & ~scan_align;
+
 	size = d_pitch * image->height + buf_align;
 	size &= ~buf_align;
 	dst = fb_get_buffer_offset(info, &info->pixmap, size);




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