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. Thanks, Georgi
