Re: [PATCH v4 0/5] simplefb: add clock handling code

[Geert Uytterhoeven <geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org>]

Hi Grant,

On Wed, Nov 12, 2014 at 10:57 AM, Grant Likely <grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote:
> On Wednesday, November 12, 2014, Geert Uytterhoeven
> <geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org> wrote:
>> On Tue, Nov 11, 2014 at 10:49 PM, Grant Likely <grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote:
>> > However, I am concerned about handover. I've lost track over the entire
>> > thread on whether the handover mechanism has been resolved, and I would
>> > really like to have a proposed solution to this documented in the
>> > binding. The fact that there is nothing tying the simple framebuffer to
>> > the actual hardware backing the framebuffer is concerning. It means the
>> > kernel needs to guess which graphics device is associated with the
>> > framebuffer.
>>
>> We did discuss handover in Düsseldorf, and concluded that the simplefb's
>> regs property can be used for this.
>>
>> While on a modern system with unified memory this association cannot be
>> derived in a generic way, a device-specific driver for the graphics hardware
>> can if the regs property of the simplefb node matches the address the CRTC
>> engine is configured for.
>
> ???
>
> Right, I'm going to be blunt here: That's just dumb. All the
> capability needed is there in the DT to associate a simple FB to a
> display controller, and the solution chosen is to use a heuristic?
>
> The association needs to be explicit. I strongly prefer putting the
> simple FB directly into the display controller node, but I would
> consider phandle linkage also.

IFF there's a display controller node, you can put it there.
I actually proposed to have a minimal/preliminary display controller node,
but people countered that for various reasons (too many components
with multiple nodes on many systems, bindings not yet defined, etc.).

And if there's no graphics driver/bindings yet at the time the bootloader
is written, it doesn't know how to link simplefb with it in DT.
Hence the heuristic to match regs... Does that make sense?

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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