Re: [PATCH v10 0/8] Introduce on-chip interconnect API

[Georgi Djakov]

On 1/10/19 18:29, Greg Kroah-Hartman wrote:
> 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@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.
>>
>> 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

Ok, i was expecting that. Thanks for confirming!

BR,
Georgi