[PATCH V2] video: implement a simple framebuffer driver

[Geert Uytterhoeven]

On Thu, May 2, 2013 at 8:25 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
> On 04/29/2013 04:04 PM, Arnd Bergmann wrote:
>> On Monday 29 April 2013, Laurent Pinchart wrote:
>>> On Monday 29 April 2013 23:31:30 Tomasz Figa wrote:
>>>
>>>> Good point. Stephen, would it be a problem to make this a KMS driver
>>>> instead? Old fbdev API could be emulated on top of it, until it goes out
>>>> of use, couldn't it?
>>>
>>> There's already an fbdev emulation layer in KMS, for such a simple use case it
>>> will work fine.
>>
>> I suggested the same to Stephen when he first brought up this driver.
>> Unfortunately his attempt to create a simple KMS driver resulted in a
>> significantly larger driver than the one he did for the framebuffer
>> interface. This means that either Stephen did something really wrong
>> in his attempt, or the KMS interface isn't as good as it should be
>> if we want to move people away from frame buffer drivers.
>
> Well, I didn't actually attempt to write the KMS driver; I simply took a
> look at existing KMS drivers (and perhaps some stub KMS driver; I forget
> right now) to see what it'd take, and it looked quite scary.
>
> The other issue is that the KMS semantics appear to desire that the
> driver allocate FB memory from some pool, and then point the display
> scanout at the allocated memory. However, this driver's semantics are
> that some other entity has allocated and reserved some memory region for
> scanout, and the simple FB driver exists solely to scribble to that
> memory region. Rob Clark said the thought this could be handled by
> writing a custom memory allocator to support this, but it seemed a
> little pointless to write a whole memory allocator when the existing FB
> interface allows the driver to just set a struct member to the address
> and be done with it.

I'm also curious to see the code for the first real simplekms/vesakms/ofkms/...
driver...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at 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