Subject: [RFC PATCH v2 00/11] Simple QoS for exynos-bus driver using interconnect

From: Artur Świgoń <[email-masked]>
Date: Thu, 19 Sep 2019 16:22:25 +0200

The following patchset adds interconnect[1][2] framework support to the
exynos-bus devfreq driver. Extending the devfreq driver with interconnect
capabilities started as a response to the issue referenced in [3]. The
patches can be subdivided into four logical groups:

(a) Refactoring the existing devfreq driver in order to improve readability
and accommodate for adding new code (patches 01--04/11).

(b) Tweaking the interconnect framework to support the exynos-bus use case
(patches 05--07/11). Exporting of_icc_get_from_provider() allows us to
avoid hardcoding every single graph edge in the DT or driver source, and
relaxing the requirement contained in that function removes the need to
provide dummy node IDs in the DT. Adjusting the logic in
apply_constraints() (drivers/interconnect/core.c) accounts for the fact
that every bus is a separate entity and therefore a separate interconnect
provider, albeit constituting a part of a larger hierarchy.

(c) Implementing interconnect providers in the exynos-bus devfreq driver
and adding required DT properties for one selected platform, namely
Exynos4412 (patches 08--09/11). Due to the fact that this aims to be a
generic driver for various Exynos SoCs, node IDs are generated dynamically
rather than hardcoded. This has been determined to be a simpler approach,
but depends on changes described in (b).

(d) Implementing a sample interconnect consumer for exynos-mixer targeted
at the issue referenced in [3], again with DT info only for Exynos4412
(patches 10--11/11).

Integration of devfreq and interconnect functionalities is achieved by
using dev_pm_qos_*() API[5]. All new code works equally well when
CONFIG_INTERCONNECT is 'n' (as in exynos_defconfig) in which case all
interconnect API functions are no-ops.

This patchset depends on [5].

--- Changes since v1 [6]:
* Rebase on [4] (coupled regulators).
* Rebase on [5] (dev_pm_qos for devfreq).
* Use dev_pm_qos_*() API[5] instead of overriding frequency in
  exynos_bus_target().
* Use IDR for node ID allocation.
* Avoid goto in functions extracted in patches 01 & 02 (cf. patch 04).
* Reverse order of multiplication and division in
  mixer_set_memory_bandwidth() (patch 11) to avoid integer overflow.

---
Artur Świgoń
Samsung R&D Institute Poland
Samsung Electronics

---
References:
[1] Documentation/interconnect/interconnect.rst
[2] Documentation/devicetree/bindings/interconnect/interconnect.txt
[3] https://patchwork.kernel.org/patch/10861757/ (original issue)
[4] https://patchwork.kernel.org/cover/11083663/ (coupled regulators; merged)
[5] https://patchwork.kernel.org/cover/11149497/ (dev_pm_qos for devfreq)
[6] https://patchwork.kernel.org/cover/11054417/ (v1 of this RFC)

Artur Świgoń (10):
  devfreq: exynos-bus: Extract exynos_bus_profile_init()
  devfreq: exynos-bus: Extract exynos_bus_profile_init_passive()
  devfreq: exynos-bus: Change goto-based logic to if-else logic
  devfreq: exynos-bus: Clean up code
  interconnect: Export of_icc_get_from_provider()
  interconnect: Relax requirement in of_icc_get_from_provider()
  interconnect: Relax condition in apply_constraints()
  arm: dts: exynos: Add parents and #interconnect-cells to Exynos4412
  devfreq: exynos-bus: Add interconnect functionality to exynos-bus
  arm: dts: exynos: Add interconnects to Exynos4412 mixer

Marek Szyprowski (1):
  drm: exynos: mixer: Add interconnect support

 .../boot/dts/exynos4412-odroid-common.dtsi    |   1 +
 arch/arm/boot/dts/exynos4412.dtsi             |  10 +
 drivers/devfreq/exynos-bus.c                  | 319 +++++++++++++-----
 drivers/gpu/drm/exynos/exynos_mixer.c         |  71 +++-
 drivers/interconnect/core.c                   |  12 +-
 include/linux/interconnect-provider.h         |   6 +
 6 files changed, 327 insertions(+), 92 deletions(-)

-- 
2.17.1

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