# Re: \[PATCH\] gma500: gtt based hardware scrolling console

- List: linux-fbdev
- 3 messages, 2 authors
- Page: https://ratatoskr.run/linux-fbdev/2011/09/3766518/t

## Re: \[PATCH\] gma500: gtt based hardware scrolling console

- From: Geert Uytterhoeven \<geert@linux-m68k.org\>
- Date: 2011-09-22 19:40:23 
- Message: https://ratatoskr.run/linux-fbdev/2011/09/3766518.md

```text
Hi Alan,

On Thu, Sep 22, 2011 at 20:43, Alan Cox [ref] wrote:
diff --git a/drivers/staging/gma500/framebuffer.c
b/drivers/staging/gma500/framebuffer.c
index 7748331..3f39a37 100644
--- a/drivers/staging/gma500/framebuffer.c
+++ b/drivers/staging/gma500/framebuffer.c

> @@ -416,6 +473,8 @@ static int psbfb_create(struct psb_fbdev *fbdev,
>
>        info->fix.smem_start = dev->mode_config.fb_base;
>        info->fix.smem_len = size;
> +       info->fix.ywrapstep = gtt_roll;

Do you really want to set this? I didn't see any other wrapping
support in your patch.
However, I guess you can implement wrapping support using the same
mapping trick?

> +       info->fix.ypanstep = gtt_roll;
>
>        if (backing->stolen) {
>                /* Accessed stolen memory directly */

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
```

## Re: \[PATCH\] gma500: gtt based hardware scrolling console

- From: Alan Cox \<hidden\>
- Date: 2011-09-22 20:23:35 
- Message: https://ratatoskr.run/linux-fbdev/2011/09/3766533.md

```text
> > +       info->fix.ywrapstep = gtt_roll;
> 
> Do you really want to set this? I didn't see any other wrapping
> support in your patch.
> However, I guess you can implement wrapping support using the same
> mapping trick?

It is actually wrapping - it writes the low pages back below the high
ones so it works the GTT as a circular buffer - or am I misunderstanding
this.

One thing I wasn't sure of on the fb side. If I've got a display width
that is annoying and can't fit on a 4Kbyte stride am I right in thinking
I can set this to say 8 and use a 512 byte stride and still get
acceleration for the usual font choice ?

Alan
```

## Re: \[PATCH\] gma500: gtt based hardware scrolling console

- From: Geert Uytterhoeven \<geert@linux-m68k.org\>
- Date: 2011-09-23 05:17:07 
- Message: https://ratatoskr.run/linux-fbdev/2011/09/3766665.md

```text
On Thu, Sep 22, 2011 at 22:21, Alan Cox [ref] wrote:
>> > +       info->fix.ywrapstep = gtt_roll;
>>
>> Do you really want to set this? I didn't see any other wrapping
>> support in your patch.
>> However, I guess you can implement wrapping support using the same
>> mapping trick?
>
> It is actually wrapping - it writes the low pages back below the high
> ones so it works the GTT as a circular buffer - or am I misunderstanding
> this.

Then it should not set ypanstep to a non-zero value, and set/handle the other
various *YWRAP flags, to communicate with the frame buffer console driver.

Panning is moving inside a virtual screen bigger than the visible screen size.

> One thing I wasn't sure of on the fb side. If I've got a display width
> that is annoying and can't fit on a 4Kbyte stride am I right in thinking
> I can set this to say 8 and use a 512 byte stride and still get
> acceleration for the usual font choice ?

Yep, that should work. The console code can use ywrap resp. ypan if the
font height is a multiple of ywrapstep resp. ypanstep.

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
```