You realize that Ville has implemented all this already and his patches are only waiting for review? -Daniel On Thu, Jan 15, 2015 at 2:50 PM, Thulasimani, Sivakumar <sivakumar.thulasimani@xxxxxxxxx> wrote: > Hi, > > I’ll be working on implementing Dynamic Voltage Frequency > Scaling in i915, whose rough proposal is provided below. Please go through > the options and provide your feedback. > > > > What is DVFS ? > > Any SKU is capable of running at more than one display CD > clock value but is configured to a default value during boot and is left > untouched afterwards. Lowering this Display CD clock will result in better > power savings while raising this will result in capability to support larger > resolution displays. So the best scenario is to always detect the attached > displays and adjust the CD Clock to the minimum required by the displays. > DVFS is the process of dynamically changing the display CD clock based on > attached displays. > > > > Usecases: ( considers low resolution LFP is used with 4K HDMI panel) > > Ø EDP (19x10) LFP panel alone is present at boot and can be driven with > lower CD clock, thus saving power. > > Ø EDP (19x10) LFP panel was present at boot and 4K HDMI display is hot > plugged in to the system. CD clock can be increased to the required value > and then we can drive 4K panel. Thus save power while only LFP is in use but > also provide the ability to support 4K displays. > > Ø 4K HDMI display is unplugged from the system, CD clock can now be lowered > to the value required to drive LFP alone to save power. > > Ø Boot with LFP and 4K HDMI connected, the CD clock will be programmed to > the value required to drive 4K HDMI. > > > > Technical Restrictions: > > Ø DVFS can be performed only when all displays are turned off > (pipe/port/plane,etc) > > > > Ux Restrictions: > > Ø Flash/flicker should be avoided as much as possible( i.e during unplug of > HDMI avoid immediately lowering the CD clock after hotunplug since it will > result in flicker on LFP ) > > > > Possible Solutions : > > Ø Policy + implementation in driver > > o Driver will set the cd clock during boot based on attached panels > > o Post boot driver has to track each modeset for CD clock and resolution > support. > > o If any change in CD clock is needed, driver has to disable all displays > , change the cd clock and enable back all displays > > o Pros: > > · Changes are contained within driver > > o Cons: > > · Complexity increases within driver > > · User land/ HWC will be blind to internal operations > > Ø Policy in HWC and implementation in driver > > o Driver will set the cd clock during boot based on attached panels > > o Post boot, driver will fail any modeset that cannot be supported > > o HWC will be responsible for disabling all displays, issuing IOCTL to > change CD clock and enabling required displays > > o Pros: > > · Driver implementation will be simple and clean > > · User land/HWC will be aware of operations and handle any special > cases such as video playback > > o Cons: > > · Solution requires HWC & Driver changes. > > > > Our recommendation is for HWC + Driver changes considering our primary > target of Android and the pros/cons mentioned there. > > > > Sorry for the long mail J, Please provide your feedback or questions on > this. > > > > regards, > > Sivakumar > > > > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > http://lists.freedesktop.org/mailman/listinfo/intel-gfx > -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
