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

Stephen Warren swarren at wwwdotorg.org
Wed Aug 13 09:38:09 PDT 2014

On 08/13/2014 01:17 AM, Luc Verhaegen wrote:
> This claims and enables clocks listed in the simple framebuffer dt node.
> This is needed so that the display engine, in case the required clocks
> are known by the kernel code and are described in the dt, will remain
> properly enabled.

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.

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.

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