Support for early wakeup in DRM

[Daniel Vetter]

On Thu, Feb 20, 2020 at 10:45:57AM -0800, jsanka at codeaurora.org wrote:
> Hello All, 
> 
> I am seeking recommendations for DRM compatible methods of updating the HW
> other than frame commit path. When exiting idle/runtime_suspend, the driver
> votes for a bunch of resources including power/clk/bandwidth as a part of
> first commit handling. This usually adds a few millisecond delay before
> processing the frame. The requirement is to find possible ways to reduce
> this delay by providing an early intimation to the framework to "prepare"
> the HW by voting for the resources and keep the HW ready to process an
> imminent frame commit. Especially in performance oriented Automotive world,
> these delays are very time critical and we are working on ways to mitigate
> them.  
> 
>  
> 
> DRM framework converges all the parameters affecting the HW in terms of DRM
> properties in a single COMMIT call. To address the above issue, we need a
> parallel channel which should allow the framework to make necessary changes
> to the HW without violating the master access privileges. 
> 
>  
> 
> Before resorting to custom downstream ways, I want to check with the
> community for folks who might have encountered and resolved such issues.

Just enable the display, which will grab all the clocks and everything?
Once the display is on a commit should be possible on the next frame, at
least for well-working drivers.
-Daniel

> 
>  
> 
> Thanks and Regards,
> 
> Jeykumar S
> 
> Qualcomm Inc.
> 
>  
> 

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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch