Re: Framebuffer with banked memory

[Antonino Daplas <adaplas@pol.net>]

On Wed, 2002-10-30 at 18:49, alain volmat wrote:
> Hi,
> 
> As I said the video card I am now writing a
> framebuffer for, doesn't have linear memory, which
> means that I can only access a small part of the
> memory at a time and then set offset registers in
> order to access another part of the memory.
> 
> I would like to know if there is such case in current
> framebuffer drivers ?? If so, what is the common
> solution to do that ??
None in the current drivers.  

> 
> In fact the problem remains in the case of mmap (which
> is the most common ;( of course), since the memory
> seams to be accessed directly by pointer, there might
> be no wait to detect if we need to set or not an
> offset. In case of fb_read fb_write, it is possible to
> do that before the actual write at the end (even if it
> is not sooo beautiful ... ).
The safest solution is to create custom fb_write? and fb_read? routines.
Maybe James will add these hooks for hardware like yours.
Then disallow mmap's except probably for the MMIO regions.

Creating a bank-switching mechanism, besides entailing a lot of work, is
not entirely safe.

Tony

PS:  What's your hardware?





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