Date:   Thu, 10 Jan 2019 17:29:06 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Georgi Djakov <georgi.djakov@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
        evgreen@...omium.org, Linux PM <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Saravana Kannan <skannan@...eaurora.org>,
        bjorn.andersson@...aro.org,
        Amit Kucheria <amit.kucheria@...aro.org>,
        seansw@....qualcomm.com, daidavid1@...eaurora.org,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        abailon@...libre.com, maxime.ripard@...tlin.com,
        Thierry Reding <thierry.reding@...il.com>,
        ksitaraman@...dia.com, sanjayc@...dia.com,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linux-tegra@...r.kernel.org, Doug Anderson <dianders@...omium.org>,
        Andy Gross <andy.gross@...aro.org>
Subject: Re: [PATCH v10 0/8] Introduce on-chip interconnect API

On Thu, Jan 10, 2019 at 04:19:14PM +0200, Georgi Djakov wrote:
> Hi Greg,
> 
> On 12/17/18 13:17, Georgi Djakov wrote:
> > 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@...aro.org> 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@...uxfoundation.org> 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@...aro.org> 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.
> 
> The dependencies for this patchset have been already merged in v5.0-rc1,
> so i was wondering if this can still go into -rc2? Various patches that
> use this API are already posted and having it sooner will make dealing
> with dependencies and merge paths a bit easier during the next merge
> window. Or i can just rebase and resend everything targeting v5.1.

We can't add new features after -rc1, sorry.

Please rebase and resend to target 5.1

thanks,

greg k-h

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