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

Chanwoo Choi
2019-12-27T00:03:17Z

On 12/27/19 6:01 AM, Rob Herring wrote:
> On Tue, Dec 17, 2019 at 02:57:33PM +0900, Chanwoo Choi wrote:
>> 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

--
Best Regards,
Chanwoo Choi
Samsung Electronics