deferred IO

[Christian Schoenebeck <cuse@users.sourceforge.net>]

Hi!

Is it possible that the deferred IO implementation in kernel 2.6.22 is buggy? 
Or do I probably misunderstand the overall concept of the FB deferred IO 
mechanism?

I wrote a framebuffer driver for a LCD which is connected via USB. As the 
video memory of the LCD is not physically available to the system (thus not 
IO memory mapped) I registered a FB deferred IO calllback function which 
performs the job of sending the new screen information via USB to the LCD 
whenever someone modified the framebuffer memory.

Unfortunately this deferred IO callback function is only called once per 
process lifetime and not (as I expected it to be) each time the framebuffer 
is actually modified.

I implemented a proc file where I could actually see the framebuffer content 
at any time and placed a:

	printk(KERN_INFO "cuselcdfb_display_update %d\n", ++i);

line in the deferred io callback to see when and how often the deferred IO 
callback function is called. So I could check that a process actually wrote 
to the framebuffer, but the callback would only be triggered once.

Any clues?

Thanks for any comments!

CU
Christian

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