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authorJaya Kumar <jayakumar.lkml@gmail.com>2008-03-19 17:01:10 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-03-19 18:53:37 -0700
commitde7c6d15e354bc94a846f03749819768c331280a (patch)
treec917a58576c73d8deb218c1e09858ebaba195697 /Documentation/fb/cmap_xfbdev.txt
parent9fedc9f1b18f6b931c3b695d7280f17fc308309b (diff)
fbdev: defio and Metronomefb
Implement support for the E-Ink Metronome controller. It provides an mmapable interface to the controller using defio support. It was tested with a gumstix pxa255 with Vizplex media using Xfbdev and various X clients such as xeyes, xpdf, xloadimage. This patch also fixes the following bug: Defio would cause a hang on write access to the framebuffer as the page fault would be called ad-infinitum. It fixes fb_defio by setting the mapping to be used by page_mkclean. Signed-off-by: Jaya Kumar <jayakumar.lkml@gmail.com> Cc: "Antonino A. Daplas" <adaplas@pol.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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+Understanding fbdev's cmap
+--------------------------
+
+These notes explain how X's dix layer uses fbdev's cmap structures.
+
+*. example of relevant structures in fbdev as used for a 3-bit grayscale cmap
+struct fb_var_screeninfo {
+ .bits_per_pixel = 8,
+ .grayscale = 1,
+ .red = { 4, 3, 0 },
+ .green = { 0, 0, 0 },
+ .blue = { 0, 0, 0 },
+}
+struct fb_fix_screeninfo {
+ .visual = FB_VISUAL_STATIC_PSEUDOCOLOR,
+}
+for (i = 0; i < 8; i++)
+ info->cmap.red[i] = (((2*i)+1)*(0xFFFF))/16;
+memcpy(info->cmap.green, info->cmap.red, sizeof(u16)*8);
+memcpy(info->cmap.blue, info->cmap.red, sizeof(u16)*8);
+
+*. X11 apps do something like the following when trying to use grayscale.
+for (i=0; i < 8; i++) {
+ char colorspec[64];
+ memset(colorspec,0,64);
+ sprintf(colorspec, "rgb:%x/%x/%x", i*36,i*36,i*36);
+ if (!XParseColor(outputDisplay, testColormap, colorspec, &wantedColor))
+ printf("Can't get color %s\n",colorspec);
+ XAllocColor(outputDisplay, testColormap, &wantedColor);
+ grays[i] = wantedColor;
+}
+There's also named equivalents like gray1..x provided you have an rgb.txt.
+
+Somewhere in X's callchain, this results in a call to X code that handles the
+colormap. For example, Xfbdev hits the following:
+
+xc-011010/programs/Xserver/dix/colormap.c:
+
+FindBestPixel(pentFirst, size, prgb, channel)
+
+dr = (long) pent->co.local.red - prgb->red;
+dg = (long) pent->co.local.green - prgb->green;
+db = (long) pent->co.local.blue - prgb->blue;
+sq = dr * dr;
+UnsignedToBigNum (sq, &sum);
+BigNumAdd (&sum, &temp, &sum);
+
+co.local.red are entries that were brought in through FBIOGETCMAP which come
+directly from the info->cmap.red that was listed above. The prgb is the rgb
+that the app wants to match to. The above code is doing what looks like a least
+squares matching function. That's why the cmap entries can't be set to the left
+hand side boundaries of a color range.
+