Hi Greg, On 12/11/18 08:58, Greg Kroah-Hartman wrote: > On Mon, Dec 10, 2018 at 04:50:00PM +0200, Georgi Djakov wrote: >> On 12/10/18 13:00, Rafael J. Wysocki wrote: >>> 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. >> >> That was the initial idea, but the problem is that there is a recent >> change in the cmd_db API (needed by the sdm845 provider driver), which >> is going through arm-soc/qcom/drivers. So either Greg pulls also the >> qcom-drivers-for-4.21 tag from Andy or the whole series goes via Olof >> and Arnd. Maybe there are other options. I don't have any preference and >> don't want to put extra burden on any maintainers, so i am ok with what >> they prefer. > > Let me take the time later this week to review the code, which I haven't > done in a while... > When you get a chance to review, please keep in mind that the latest version is v12 (from 08.Dec). The same is also available in linux-next with no reported issues. Thanks, Georgi
