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... thanks, greg k-h
