Re: overlay support

On Tue, 12 Sep 2006, Jorge Luis Zapata Muga wrote:

On 9/12/06, Geert Uytterhoeven [off-list ref] wrote:

quoted

On Tue, 12 Sep 2006, Jorge Luis Zapata Muga wrote:

quoted

i coded a while ago a framebuffer driver for an old video card i have
(a SiS 6326, just for learning) but now i would like to support its
video extension (overlay support, this card can also capture from an
external input, but my version doesnt has the input connectors). ive
read on the mailing list and on external projects about how to support
overlay on the fb device, but i still dont find a good way to do it,
maybe you can help me out.

one way is to add another fb device, but it is good only if the device
has a different memory space assigned to it, if you only have a chunk
of memory for both layers (the overlay and the normal rgb which is
this case) there should be a way to resize the memory space assigned
to each of them. i dont like this way because is adding a policy on
kernel space to manage the memory. am i correct with this assumptions?

If there are just 2 users of the memory (i.e. 2 frame buffers), you can avoid
adding a policy to the kernel by making the split dynamic.
Let the first frame buffer `allocate' (based on xres_virtual, yres_virtual, and
bits_per_pixel) from the bottom of memory, and the second frame buffer from the
top of memory. Each frame buffer can shrink whatever it wants, or grow, as long
as it doesn't conflict with the memory size of the other.

indeed, this is another solution, but what happens if the requested
size of the framebuffer will overlap the other framebuffer memory
space? wouldnt be better to manage the framebuffer memory from
userspace and use the v4l interface for the overlay?

In that case, fb_ops.fb_check_var() should return an error.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds

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