Re: How to implement rotation for framebuffer?

[Geert Uytterhoeven <geert@linux-m68k.org>]

On Fri, 4 Apr 2008, arun c wrote:
> I am working on 2430SDP. SDP has omap2430 as the processor and it's
> display controller supports rotation of framebuffer in hardware.
> 
> I will explain the hardware rotation in brief.
> 
> 1) One Physical framebuffer is allocated in memory
> 2) This physical address ( as well as width and height) is programmed in the
>     VRFB Module (the hardware rotation engine, it stands for virtual rotated
>     frame buffer)
> 3)Then VRFB gives you 4 addresses ( virtual addresses which are
> transparent to applications)
>     VBA0      --> Address for 0 degree rotation
>     VBA90    --> Address for 90 degree rotation
>     VBA180  --> Address for 180 degree rotation
>     VBA270  --> Address for 270 degree rotation
> 
> Rotation is achieved like this
> Assume you want 90 degree rotation
> 
> Processor writes all picture data to VBA90 space and lcd reads all
> data from VBA0 space
> 
> For this kind of implementation i need to change fb_fix_screeninfo
> members (smem_start ,smem_len) and fb_info member( screen_base)
> dynamically according to degree of rotation.

Yep, that's correct.

> Please anybody suggest me  good ways to implement this kind of
> rotation in my driver or point me to some code so that i can refer and
> implement the same.

Very simple: any change of struct fb_var_screeninfo may cause a change
of fb_fix_screeninfo.

Hence if an application requests to change the rotation angle by
changing fb_var_screeninfo.rotate and issuing an FBIOPUT_VSCREENINFO
ioctl, you update your fb_fix_screeninfo and fb_info.screen_base.

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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