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Subject: Re: [PATCH v10 0/8] Introduce on-chip interconnect API
From:   Georgi Djakov <georgi.djakov@linaro.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Olof Johansson <olof@lixom.net>,
        evgreen@chromium.org, Linux PM <linux-pm@vger.kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Rob Herring <robh+dt@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Kevin Hilman <khilman@baylibre.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Saravana Kannan <skannan@codeaurora.org>,
        bjorn.andersson@linaro.org,
        Amit Kucheria <amit.kucheria@linaro.org>,
        seansw@qti.qualcomm.com, daidavid1@codeaurora.org,
        Mark Rutland <mark.rutland@arm.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        abailon@baylibre.com, maxime.ripard@bootlin.com,
        Thierry Reding <thierry.reding@gmail.com>,
        ksitaraman@nvidia.com, sanjayc@nvidia.com,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        linux-tegra@vger.kernel.org, Doug Anderson <dianders@chromium.org>,
        Andy Gross <andy.gross@linaro.org>
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Message-ID: <b21d13df-7c0b-4c6d-e3c7-6ab285579ed5@linaro.org>
Date:   Thu, 10 Jan 2019 16:19:14 +0200
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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@linaro.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@linuxfoundation.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@linaro.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.

Thanks,
Georgi