Re: Qs: Kernel memory allocation; fbcon greyscale implementation

Alan Cox (alan@lxorguk.ukuu.org.uk)
Fri, 23 Apr 1999 19:06:23 +0100 (BST)


> 1) Display hardware needs a memory block for it's frame buffer from the
> main ram aligned to a 64K boundary. How do I best allocate this. Now I
> reduced the memory size reported to the kernel and ioremap'ped the top
> memory block into the virtual memory. But as this is not in control of
> the driver I think its not the correct way.

For blocks up to 128K you could use get_free_pages

> 2) The kernel message says that 412k of the memory is reserved. I'm
> afraid that the 640k-1M area is reserved and lost. If thats true, how
> can I get them back.

arch/i386/mm/init.c marks those blocks out.

> 3) The display is 16 level gray scale, 4 bpp, 2 pixels in a byte. In
> what visual type does it map nicely. It seems to me that the fbcon
> treats it as a pseudocolor device. At least the appearing logo is
> indexed color picture - I think. I don't have very clear idea how this
> affects for example the applications. I think I saw a note somewhere
> about this kind of display but from the sources I don't get the idea how
> it shoulf be implemented.

4bpp bitmapped frame buffer is supported. I originally wrote it for a mac.
If you make it report greyscale then that is what you get

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