# Re: 2.5 atyfb on Sparc question

- From: James Simmons \<hidden\>
- Date: 2002-10-18 18:20:35 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2002/10/13450487
- Thread: https://ratatoskr.run/linux-fbdev/2002/10/13450436/t.md

```text

> I thought i may as well write a little HOWTO or something such on the
> way of doing this. Since i have not much fbdev writing experience, maybe
> i am a good candidate for writing such a thing.

Wow that would be great.

> I wanted, in the first step, to do just a basic unaccelerated fbdev
> driver, without mode changes and anything fancy, and once this works,
> add things incrementally. I believe this approach will be good for
> future fbdev driver writters.

Good approach to doing this.

> Anyway, now for my question.
>
> skeletonfb says that check_var, set_par, setcolreg, pan_display and
> blank functions are optional or not required. Is that true, and in case
> i don't want to provide them, whay do i put in the fb_ops structure ?

All the functions are optional. They are needed when:

fb_open:        We need special things done when we open or close /dev/fb
fb_release:

fb_read: 	When we have a strange framebuffer that doesn't allow
fb_write:	linear writes. A good example is the Epson1385 chipset at
		16 bpp mode.

fb_check_var:   When we can change the resolution of the display.
fb_set_par:

fb_setcolreg:	Have a programable color palette.

fb_blank:	Have hardware support for power management of some kind.

fb_pan_display: Hardware scrolling

fb_cursor:	Hardware cursor.

fb_poll:	Want to use interrupts such as VLB.

fb_sync:	To sync the accel engine and framebuffer memory.

fb_ioctl:	Extra functions you want to support.

fb_mmap:	Have special memory needs when exposing to userland.

fb_rastering:	I don't know if we are going to keep this one?

The only ones require are the accel functions for drawing on the console.

> Later, in the fb_ops structure, only set_par, blank and pan_display are
> labeled as optional.

That is a mistake.



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