RE: [Linux-fbdev-devel] Framebuffer with banked memory

[James S. <jsi...@in...>]

>   The short answer to your problem is that, sadly, much of the 2.4
> framebuffer is badly implemented, allowing device independent code to
> directly access device memory etc. Some of this is cleaned up for 2.5, but
> as I've not looked at it lately I'm not sure how much.  Here are some
> pointers as to what is required for 2.4.
>
> #1 The Boot penguin code directly accesses your video memory. If you have
> banked memory this will likely fall off the end of a pointer and oops the
> kernel or worse.

Fixed in 2.5.X. You use the image drawing function to draw the penguin.

> #2 Read/Write Access video memory directly. I had added a read/write
> handler to the fb_ops to hook these out and switch banks.
> Read/write are also incorrect if your pitch != width.

Fixed. I have hooks now. I didn't notice the pitch != width problem. Give
me time to fix up a patch, unless someone bets me to the punch.

> #3 Memory map can't be done. I had coded up a working version that would
> map a single back and page fault in the banks as necessary. This worked
> but would get hung up on unaligned accesses where one instruction accessed
> two memory banks at the same time. So memory map isn't possible.

:-( Even with providing your own mmap function you still couldn't get it
to work.