linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "Artur Świgoń" <a.swigon@partner.samsung.com>
To: Georgi Djakov <georgi.djakov@linaro.org>,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-pm@vger.kernel.org, dri-devel@lists.freedesktop.org
Cc: krzk@kernel.org, cw00.choi@samsung.com, myungjoo.ham@samsung.com,
	inki.dae@samsung.com, sw0312.kim@samsung.com,
	m.szyprowski@samsung.com,
	"Bartłomiej Żołnierkiewicz" <b.zolnierkie@samsung.com>
Subject: Re: [RFC PATCH 09/11] devfreq: exynos-bus: Add interconnect functionality to exynos-bus
Date: Thu, 01 Aug 2019 09:59:42 +0200	[thread overview]
Message-ID: <62557522be4924a01d3822d4734c30f2965c608b.camel@partner.samsung.com> (raw)
In-Reply-To: <6e8b2081-2fb3-9ab8-37d1-8b5fe5fd8e11@linaro.org>

Hi Georgi,

On Fri, 2019-07-26 at 11:05 +0300, Georgi Djakov wrote:
> Hi Artur,
> 
> On 7/23/19 15:20, Artur Świgoń wrote:
> > This patch adds interconnect functionality to the exynos-bus devfreq
> > driver.
> > 
> > The SoC topology is a graph (or, more specifically, a tree) and most of its
> > edges are taken from the devfreq parent-child hierarchy (cf.
> > Documentation/devicetree/bindings/devfreq/exynos-bus.txt). The previous
> > patch adds missing edges to the DT (under the name 'parent'). Due to
> > unspecified relative probing order, -EPROBE_DEFER may be propagated to
> > guarantee that a child is probed before its parent.
> > 
> > Each bus is now an interconnect provider and an interconnect node as well
> > (cf. Documentation/interconnect/interconnect.rst), i.e. every bus registers
> > itself as a node. Node IDs are not hardcoded but rather assigned at
> > runtime, in probing order (subject to the above-mentioned exception
> > regarding relative order). This approach allows for using this driver with
> > various Exynos SoCs.
> 
> I am not familiar with the Exynos bus topology, but it seems to me that it's not
> represented correctly. An interconnect provider with just a single node (port)
> is odd. I would expect that each provider consists of multiple master and slave
> nodes. This data would be used by a framework to understand what are the links
> and how the traffic flows between the IP blocks and through which buses.

To summarize the exynos-bus topology[1] used by the devfreq driver: There are
many data buses for data transfer in Samsung Exynos SoC. Every bus has its own
clock. Buses often share power lines, in which case one of the buses on the
power line is referred to as 'parent' (or as 'devfreq' in the DT). In the
particular case of Exynos4412[1][2], the topology can be expressed as follows:

bus_dmc
-- bus_acp
-- bus_c2c

bus_leftbus
-- bus_rightbus
-- bus_display
-- bus_fsys
-- bus_peri
-- bus_mfc

Where bus_dmc and bus_leftbus probably could be referred to as masters, and the
following indented nodes as slaves. Patch 08/11 of this RFC additionally adds
the following to the DT:

bus_dmc
-- bus_leftbus

Which makes the topology a valid tree.

The exynos-bus concept in devfreq[3] is designed in such a way that every bus is
probed separately as a platform device, and is a largely independent entity.
This RFC proposes an extension to the existing devfreq driver that basically
provides a simple QoS to ensure minimum clock frequency for selected buses
(possibly overriding devfreq governor calculations) using the interconnect
framework.

The hierarchy is modelled in such a way that every bus is an interconnect node.
On the other hand, what is considered an interconnect provider here is quite
arbitrary, but for the reasons mentioned in the above paragraph, this RFC
assumes that every bus is a provider of itself as a node. Using an alternative
singleton provider approach was deemed more complicated since the 'dev' field in
'struct icc_provider' has to be set to something meaningful and we are tied to
the 'samsung,exynos-bus' compatible string in the driver (and multiple instances
of exynos-bus probed in indeterminate relative order).

I'm looking forward to hearing any additional thoughts you may have on this
topic.

Best regards,
-- 
Artur Świgoń
Samsung R&D Institute Poland
Samsung Electronics

[1] Documentation/devicetree/bindings/devfreq/exynos-bus.txt
[2]
arch/arm/boot/dts/exynos4412-odroid-common.dtsi
[3] drivers/devfreq/exynos-bus.c
(subject of this patch)



  reply	other threads:[~2019-08-01  7:59 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20190723122022eucas1p2f568f74f981f9de9012eb693c3b446d5@eucas1p2.samsung.com>
2019-07-23 12:20 ` [RFC PATCH 00/11] Simple QoS for exynos-bus driver using interconnect Artur Świgoń
     [not found]   ` <CGME20190723122022eucas1p1266d90873d564894bd852c20140f8474@eucas1p1.samsung.com>
2019-07-23 12:20     ` [RFC PATCH 01/11] devfreq: exynos-bus: Extract exynos_bus_profile_init() Artur Świgoń
2019-07-24 19:07       ` Krzysztof Kozlowski
2019-07-31 13:00         ` Artur Świgoń
2019-08-05  9:56           ` Krzysztof Kozlowski
2019-07-25 12:43       ` Chanwoo Choi
2019-07-26 10:42         ` Krzysztof Kozlowski
2019-07-26 10:52           ` Chanwoo Choi
     [not found]   ` <CGME20190723122023eucas1p2ff56c00b60a676ed85d9fe159a1839f2@eucas1p2.samsung.com>
2019-07-23 12:20     ` [RFC PATCH 02/11] devfreq: exynos-bus: Extract exynos_bus_profile_init_passive() Artur Świgoń
2019-07-24 19:08       ` Krzysztof Kozlowski
2019-07-25 12:45       ` Chanwoo Choi
     [not found]   ` <CGME20190723122024eucas1p1ff060d072132bfbc8a8a1d10fa1f90f8@eucas1p1.samsung.com>
2019-07-23 12:20     ` [RFC PATCH 03/11] devfreq: exynos-bus: Change goto-based logic to if-else logic Artur Świgoń
2019-07-24 19:10       ` Krzysztof Kozlowski
2019-07-25 12:56       ` Chanwoo Choi
2019-07-25 13:02         ` Chanwoo Choi
     [not found]   ` <CGME20190723122024eucas1p25a480ccddaa69ee1d0f1a07960ca3f22@eucas1p2.samsung.com>
2019-07-23 12:20     ` [RFC PATCH 04/11] devfreq: exynos-bus: Clean up code Artur Świgoń
2019-07-24 19:14       ` Krzysztof Kozlowski
2019-07-25 12:50       ` Chanwoo Choi
2019-07-26 10:45         ` Krzysztof Kozlowski
2019-07-26 11:04           ` Chanwoo Choi
     [not found]   ` <CGME20190723122025eucas1p251df372451e0b27ad7f2e3c89df60b64@eucas1p2.samsung.com>
2019-07-23 12:20     ` [RFC PATCH 05/11] icc: Export of_icc_get_from_provider() Artur Świgoń
2019-07-24 19:15       ` Krzysztof Kozlowski
     [not found]   ` <CGME20190723122026eucas1p2acf705de2a47ba54f383d916f5383144@eucas1p2.samsung.com>
2019-07-23 12:20     ` [RFC PATCH 06/11] icc: Relax requirement in of_icc_get_from_provider() Artur Świgoń
2019-07-24 19:16       ` Krzysztof Kozlowski
     [not found]   ` <CGME20190723122027eucas1p124f44370a63b16dcb765585761d661a3@eucas1p1.samsung.com>
2019-07-23 12:20     ` [RFC PATCH 07/11] icc: Relax condition in apply_constraints() Artur Świgoń
     [not found]   ` <CGME20190723122027eucas1p24b1d76e3139f7cc52614d7613ff9ba98@eucas1p2.samsung.com>
2019-07-23 12:20     ` [RFC PATCH 08/11] arm: dts: exynos: Add parents and #interconnect-cells to Exynos4412 Artur Świgoń
2019-07-24 19:24       ` Krzysztof Kozlowski
2019-07-31 13:00         ` Artur Świgoń
2019-07-25 13:13       ` Chanwoo Choi
2019-07-26 12:02         ` Marek Szyprowski
2019-07-29  1:20           ` Chanwoo Choi
     [not found]   ` <CGME20190723122028eucas1p2eb75f35b810e71d6c590370aaff0997b@eucas1p2.samsung.com>
2019-07-23 12:20     ` [RFC PATCH 09/11] devfreq: exynos-bus: Add interconnect functionality to exynos-bus Artur Świgoń
2019-07-24 18:36       ` Krzysztof Kozlowski
2019-07-31 13:01         ` Artur Świgoń
2019-07-26  8:05       ` Georgi Djakov
2019-08-01  7:59         ` Artur Świgoń [this message]
2019-08-07 14:21           ` Georgi Djakov
2019-08-08 13:28             ` Artur Świgoń
2019-07-29  1:52       ` Chanwoo Choi
2019-08-08 13:18         ` Artur Świgoń
2019-08-09  2:17           ` Chanwoo Choi
2019-08-08 15:00         ` Leonard Crestez
2019-08-19 23:44           ` Chanwoo Choi
2019-08-06 13:41       ` Leonard Crestez
2019-08-08 13:19         ` Artur Świgoń
     [not found]   ` <CGME20190723122029eucas1p21e1a51e759f9b605d2c89daf659af7bb@eucas1p2.samsung.com>
2019-07-23 12:20     ` [RFC PATCH 10/11] arm: dts: exynos: Add interconnects to Exynos4412 mixer Artur Świgoń
     [not found]   ` <CGME20190723122029eucas1p2915f536d9ef43a7bd043a878a553439f@eucas1p2.samsung.com>
2019-07-23 12:20     ` [RFC PATCH 11/11] drm: exynos: mixer: Add interconnect support Artur Świgoń
2019-07-24 18:52       ` Krzysztof Kozlowski
2019-07-24 18:53   ` [RFC PATCH 00/11] Simple QoS for exynos-bus driver using interconnect Krzysztof Kozlowski
2019-08-13  6:17   ` Chanwoo Choi
2019-08-13  6:19     ` Chanwoo Choi

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=62557522be4924a01d3822d4734c30f2965c608b.camel@partner.samsung.com \
    --to=a.swigon@partner.samsung.com \
    --cc=b.zolnierkie@samsung.com \
    --cc=cw00.choi@samsung.com \
    --cc=devicetree@vger.kernel.org \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=georgi.djakov@linaro.org \
    --cc=inki.dae@samsung.com \
    --cc=krzk@kernel.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pm@vger.kernel.org \
    --cc=linux-samsung-soc@vger.kernel.org \
    --cc=m.szyprowski@samsung.com \
    --cc=myungjoo.ham@samsung.com \
    --cc=sw0312.kim@samsung.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).