Thanks for your answer, but it implied some other questions :-)

You said, that accelerated functions are called from console - so programs wich are drawing directly to FB (like QT embedded in my case) have no profit from them? Or do they?

What is actually the best technique of using FB (for achieving the best performance) - should i malloc a piece of RAM, draw to it and then memmove it to FB mapped address as a whole frame or draw directly to FB? Or it doesnt matter?

When i greped through drivers sources i was expecting that accelerated drivers will use mmap only for registers and that the imageblit function would be implemented as some DMA fetching from system memory. But i was wrong, there are still mmaps to video memory. So i want to ask, if that idea is completely wrong and why drivers of GPUs use mmap to video mem, when they have DMA controller.

Thank you for your time.

Rene

 ------------ Pùvodní zpráva ------------
 Od: Ondrej Zajicek [off-list ref]
 Pøedmìt: Re: [Linux-fbdev-devel] framebuffer general questions
 Datum: 13.11.2009 21:06:52
 ----------------------------------------
 On Fri, Nov 13, 2009 at 03:11:48PM +0100, René Kolaøík wrote:
 > Hi
 > 
 > i am trying to customize framebuffer drivers and i have some questions...
 > 
 > Please can you give me an advice? 
 > 
 > 1) If I define my own imageblit function, how do I call it? Or is it called
 automatically?
 
 It is called automatically (if it is registered in fb_ops structure)
 from kernel console. It is not possible to call it from userspace.
 
 > 2) I have gpu connected via pci to cpu. I did mmap and have
 > framebuffer mapped in for example "uchar * data". I have loop and
 > iterating through some pixel data and do data[i] = pixel[i]. Does this
 > lead to transmitting via PCI in style - transmit byte ... end ...
 > transmit byte ... end ... etc?
 
 Probably yes, perhaps there is some write combining according to MTRR
 registers.
 
 > 3)what is the difference bethween mmap framebuffer and write to mapped
 > pointer and calling write() to descriptor previously obtained by open()?
 
 The first variant is much faster - video RAM is directly mapped to userspace 
 address space, therefore there is no kernel interaction during writes (in
 usual fbdev drivers).
 
 -- 
 Elen sila lumenn' omentielvo
 
 Ondrej 'SanTiago' Zajicek (email: santiago@crfreenet.org)
 OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
 "To err is human -- to blame it on a computer is even more so."
 
 
 

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