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

Chanwoo Choi
2020-01-06T01:31:31Z

Hi Rob,

Gently Ping.

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

Are there any other commentss?

--
Best Regards,
Chanwoo Choi
Samsung Electronics