Re: [PATCH 4/9] PM / devfreq: exynos-bus: Replace deprecated 'devfreq' property

Hi Rob,

On Mon, Jan 6, 2020 at 10:32 AM Chanwoo Choi [off-list ref] wrote:

Hi Rob,

Gently Ping.

Once again, ping. Could you please review?

On v2[1], made separate patches for dt-binding.
[1] https://patchwork.kernel.org/cover/11304545/

On 12/27/19 9:09 AM, Chanwoo Choi wrote:

quoted

On 12/27/19 6:01 AM, Rob Herring wrote:

quoted

On Tue, Dec 17, 2019 at 02:57:33PM +0900, Chanwoo Choi wrote:

quoted

In order to remove the deprecated 'devfreq' property, replace with
new 'exynos,parent-bus' property in order to get the parent devfreq device
in devicetree file instead of 'devfreq' property. But, to guarantee the
backward-compatibility, keep the support 'devfreq' property.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
---
 .../bindings/devfreq/exynos-bus.txt           | 16 +++++++--------
 drivers/devfreq/exynos-bus.c                  | 20 ++++++++++++-------
 2 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/Documentation/devicetree/bindings/devfreq/exynos-bus.txt b/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
index e71f752cc18f..c948cee01124 100644
--- a/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
+++ b/Documentation/devicetree/bindings/devfreq/exynos-bus.txt

@@ -45,7 +45,7 @@ Required properties only for parent bus device:
   of buses.

 Required properties only for passive bus device:
-- devfreq: the parent bus device.
+- exynos,parent-bus: the parent bus device.

If you are going to do something new, why not use the interconnect
binding here?

As I knew, interconnect make the data path among multiple nodes
and set the average and peak bandwidth to the specific data path.

It means that some data will be flowed from node_a to node_d
or the reverse way because each node has the tightly coupled
dependency for data flow.

      node_a <-> node_b <-> node_c <-> node_d


On the other hand, exynos-bus.c driver is not related to 'data path'.
Each bus just need to control the their own frequency and voltage.
But, share the power line (regulator) between exynos-bus device
even if there are no any dependency of data flow.

'exynos,parent-bus' property just indicate the specific
devfreq device(parent bus device) which controls
the shared power line(regulator) in order to prevent
the h/w problem due to the wrong pair of frequency and voltage.

'exynos,parent-bus' property is only used to catch
the change timing of shared power line.


And,
as you commented, there are some data path among the exynos-bus
devices for the display h/w as following:

      bus_display -> bus_leftbus -> bus_dmc

In order to make the data path between bus devices,
interconnect binding is required. This approach[1] was posted.
[1] https://patchwork.kernel.org/cover/11305265/
- [RFC,v3,0/7] PM / devfreq: Simple QoS for exynos-bus using interconnect

Are there any other commentss?


--
Best Regards,
Chanwoo Choi
Samsung Electronics

-- 
Best Regards,
Chanwoo Choi

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