[PATCH 4/4] simplefb: add clock handling code

[Luc Verhaegen]

On Wed, Aug 13, 2014 at 10:38:09AM -0600, Stephen Warren wrote:
>
> I think this make simplefb not simple any more, which rather goes  
> against the whole point of it.
>
> I specifically conceived simplefb to know about nothing more than the  
> memory address and pixel layout of the memory buffer. I certainly don't  
> like the idea of expanding simplefb to anything beyond that, and IIRC  
> *not* extending is was a condition agreed when it was first merged. If  
> more knowledge than that is required, then there needs to be a  
> HW-specific driver to manage any clocks/resets/video registers, etc.

Yes. Simplefb quickly becomes anything but, doesn't it. Perhaps DenialFB 
would've been a better name for it ;p

> The correct way to handle this without a complete DRM/KMS/... driver is  
> to avoid the clocks in question being turned off at boot. I thought  
> there was a per-clock flag to prevent disabling an unused clock? If not,  
> perhaps the clock driver should force the clock to be enabled (perhaps  
> only if the DRM/KMS driver isn't enabled?). For example, the Tegra clock  
> driver has a clock initialization table which IIRC was used for this  
> purpose before we got a DRM/KMS driver. That way, all the details are  
> kept inside the kernel code, and don't end up influencing the DT  
> representation of simplefb.

How was simplefb handled on tegra? Where is the code for that? I didn't 
see anything in u-boot for instance.

But the code for handling clocks where they are supposed to be handled 
is pretty generic from where i sit.

Luc Verhaegen.