[PATCH] framebuffer: new driver for cyberblade/i1 graphics core
This is a framebuffer driver for the Cyberblade/i1 graphics core.
Currently tridenfb claims to support the cyberblade/i1 graphics core. This
is of very limited truth. Even vesafb is faster and provides more working
modes and a much better quality of the video signal. There is a great
number of bugs in tridentfb ... but most often it is impossible to decide
if these bugs are real bugs or if fixing them for the cyberblade/i1 core
would break support for one of the other supported chips.
Tridentfb seems to be unmaintained,and documentation for most of the
supported chips is not available. So "fixing" cyberblade/i1 support inside
of tridentfb was not an option, it would have caused numerous
if(CYBERBLADEi1) else ... cases and would have rendered the code to be
almost unmaintainable.
A first version of this driver was published on 2005-07-31. A fix for a
bug reported by Jochen Hein was integrated as well as some changes
requested by Antonino A. Daplas.
A message has been added to tridentfb to inform current users of tridentfb
to switch to cyblafb if the cyberblade/i1 graphics core is detected.
This patch is one logical change, but because of the included documentation
it is bigger than 70kb. Therefore it is not sent to lkml and
linux-fbdev-devel,
Signed-off-by: Knut Petersen <Knut_Petersen@t-online.de>
Cc: Muli Ben-Yehuda <mulix@mulix.org>
Acked-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/Documentation/fb/cyblafb/whycyblafb b/Documentation/fb/cyblafb/whycyblafb
new file mode 100644
index 0000000..a123bc1
--- /dev/null
+++ b/Documentation/fb/cyblafb/whycyblafb
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+I tried the following framebuffer drivers:
+
+ - TRIDENTFB is full of bugs. Acceleration is broken for Blade3D
+ graphics cores like the cyberblade/i1. It claims to support a great
+ number of devices, but documentation for most of these devices is
+ unfortunately not available. There is _no_ reason to use tridentfb
+ for cyberblade/i1 + CRT users. VESAFB is faster, and the one
+ advantage, mode switching, is broken in tridentfb.
+
+ - VESAFB is used by many distributions as a standard. Vesafb does
+ not support mode switching. VESAFB is a bit faster than the working
+ configurations of TRIDENTFB, but it is still too slow, even if you
+ use ypan.
+
+ - EPIAFB (you'll find it on sourceforge) supports the Cyberblade/i1
+ graphics core, but it still has serious bugs and developement seems
+ to have stopped. This is the one driver with TV-out support. If you
+ do need this feature, try epiafb.
+
+None of these drivers was a real option for me.
+
+I believe that is unreasonable to change code that announces to support 20
+devices if I only have more or less sufficient documentation for exactly one
+of these. The risk of breaking device foo while fixing device bar is too high.
+
+So I decided to start CyBlaFB as a stripped down tridentfb.
+
+All code specific to other Trident chips has been removed. After that there
+were a lot of cosmetic changes to increase the readability of the code. All
+register names were changed to those mnemonics used in the datasheet. Function
+and macro names were changed if they hindered easy understanding of the code.
+
+After that I debugged the code and implemented some new features. I'll try to
+give a little summary of the main changes:
+
+ - calculation of vertical and horizontal timings was fixed
+
+ - video signal quality has been improved dramatically
+
+ - acceleration:
+
+ - fillrect and copyarea were fixed and reenabled
+
+ - color expanding imageblit was newly implemented, color
+ imageblit (only used to draw the penguine) still uses the
+ generic code.
+
+ - init of the acceleration engine was improved and moved to a
+ place where it really works ...
+
+ - sync function has a timeout now and tries to reset and
+ reinit the accel engine if necessary
+
+ - fewer slow copyarea calls when doing ypan scrolling by using
+ undocumented bit d21 of screen start address stored in
+ CR2B[5]. BIOS does use it also, so this should be safe.
+
+ - cyblafb rejects any attempt to set modes that would cause vclk
+ values above reasonable 230 MHz. 32bit modes use a clock
+ multiplicator of 2, so fbset does show the correct values for
+ pixclock but not for vclk in this case. The fbset limit is 115 MHz
+ for 32 bpp modes.
+
+ - cyblafb rejects modes known to be broken or unimplemented (all
+ interlaced modes, all doublescan modes for now)
+
+ - cyblafb now works independant of the video mode in effect at startup
+ time (tridentfb does not init all needed registers to reasonable
+ values)
+
+ - switching between video modes does work reliably now
+
+ - the first video mode now is the one selected on startup using the
+ vga=???? mechanism or any of
+ - 640x480, 800x600, 1024x768, 1280x1024
+ - 8, 16, 24 or 32 bpp
+ - refresh between 50 Hz and 85 Hz, 1 Hz steps (1280x1024-32
+ is limited to 63Hz)
+
+ - pci retry and pci burst mode are settable (try to disable if you
+ experience latency problems)
+
+ - built as a module cyblafb might be unloaded and reloaded using
+ the vfb module and con2vt or might be used together with vesafb
+