On Mon, Dec 10, 2018 at 11:18 AM Georgi Djakov <georgi.djakov@xxxxxxxxxx> wrote: > > Hi Rafael, > > On 12/10/18 11:04, Rafael J. Wysocki wrote: > > On Thu, Dec 6, 2018 at 3:55 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > >> > >> On Wed, Dec 05, 2018 at 12:41:35PM -0800, Evan Green wrote: > >>> On Tue, Nov 27, 2018 at 10:03 AM Georgi Djakov <georgi.djakov@xxxxxxxxxx> wrote: > >>>> > >>>> Modern SoCs have multiple processors and various dedicated cores (video, gpu, > >>>> graphics, modem). These cores are talking to each other and can generate a > >>>> lot of data flowing through the on-chip interconnects. These interconnect > >>>> buses could form different topologies such as crossbar, point to point buses, > >>>> hierarchical buses or use the network-on-chip concept. > >>>> > >>>> These buses have been sized usually to handle use cases with high data > >>>> throughput but it is not necessary all the time and consume a lot of power. > >>>> Furthermore, the priority between masters can vary depending on the running > >>>> use case like video playback or CPU intensive tasks. > >>>> > >>>> Having an API to control the requirement of the system in terms of bandwidth > >>>> and QoS, so we can adapt the interconnect configuration to match those by > >>>> scaling the frequencies, setting link priority and tuning QoS parameters. > >>>> This configuration can be a static, one-time operation done at boot for some > >>>> platforms or a dynamic set of operations that happen at run-time. > >>>> > >>>> This patchset introduce a new API to get the requirement and configure the > >>>> interconnect buses across the entire chipset to fit with the current demand. > >>>> The API is NOT for changing the performance of the endpoint devices, but only > >>>> the interconnect path in between them. > >>> > >>> For what it's worth, we are ready to land this in Chrome OS. I think > >>> this series has been very well discussed and reviewed, hasn't changed > >>> much in the last few spins, and is in good enough shape to use as a > >>> base for future patches. Georgi's also done a great job reaching out > >>> to other SoC vendors, and there appears to be enough consensus that > >>> this framework will be usable by more than just Qualcomm. There are > >>> also several drivers out on the list trying to add patches to use this > >>> framework, with more to come, so it made sense (to us) to get this > >>> base framework nailed down. In my experiments this is an important > >>> piece of the overall power management story, especially on systems > >>> that are mostly idle. > >>> > >>> I'll continue to track changes to this series and we will ultimately > >>> reconcile with whatever happens upstream, but I thought it was worth > >>> sending this note to express our "thumbs up" towards this framework. > >> > >> Looks like a v11 will be forthcoming, so I'll wait for that one to apply > >> it to the tree if all looks good. > > > > I'm honestly not sure if it is ready yet. > > > > New versions are coming on and on, which may make such an impression, > > but we had some discussion on it at the LPC and some serious questions > > were asked during it, for instance regarding the DT binding introduced > > here. I'm not sure how this particular issue has been addressed here, > > for example. > > There have been no changes in bindings since v4 (other than squashing > consumer and provider bindings into a single patch and fixing typos). > > The last DT comment was on v9 [1] where Rob wanted confirmation from > other SoC vendors that this works for them too. And now we have that > confirmation and there are patches posted on the list [2]. OK > The second thing (also discussed at LPC) was about possible cases where > some consumer drivers can't calculate how much bandwidth they actually > need and how to address that. The proposal was to extend the OPP > bindings with one more property, but this is not part of this patchset. > It is a future step that needs more discussion on the mailing list. If a > driver really needs some bandwidth data now, it should be put into the > driver and not in DT. After we have enough consumers, we can discuss > again if it makes sense to extract something into DT or not. That's fine by me. Admittedly, I have some reservations regarding the extent to which this approach will turn out to be useful in practice, but I guess as long as there is enough traction, the best way to find out it to try and see. :-) >From now on I will assume that this series is going to be applied by Greg. Thanks, Rafael
