mainline kernel: cpufreq for bcm2835

[Sergey Suloev]

Hi Stefan

On 04/02/2018 11:02 PM, Stefan Wahren wrote:
> Hi Sergey,
>
>> Sergey Suloev <ssuloev at orpaltech.com> hat am 2. April 2018 um 19:14 geschrieben:
>>
>>
>> On 04/02/2018 07:09 PM, Stefan Wahren wrote:
>>> Hi Sergey,
>>>
>>> [add linux-rpi-kernel]
>>>
>>>> Sergey Suloev <ssuloev at orpaltech.com> hat am 2. April 2018 um 17:45 geschrieben:
>>>>
>>>>
>>>> Hi Stefan
>>>>
>>>> can any give any hint about the status of bcn2835 cpufreq in mainline
>>>> kernel ?
>>> in short: currently no support yet
>>>
>>>> Are you (or anyone else) working on it ?
>>> No, this not on my TODO list [1].
>>>
>>> Current prio:
>>> - Raspberry Pi 3+
>>> - fixes and improvements for Raspberry Pi 3 DT
>>> - VCHIQ data corruption
>>>
>>> Implementing/Porting the cpufreq driver is only half of the work. Also all drivers which depend on the VPU core clock should be able to handle a frequency change (sdhost, i2c, aux uart comes to my mind). But i will be happy if somebody takes care of it.
>>>
>>> Is this a critical feature for you?
>>>
>>> Best regards
>>> Stefan
>>>
>>> [1] - https://github.com/lategoodbye/rpi-zero/issues
>>>
>>>> Thanks
>>>>
>> well, that seems to be a lot of work.
> maybe less than you think (apart from testing).
>
>> Is the following patch an attempt of porting the driver ?
>>
>> http://lists.infradead.org/pipermail/linux-rpi-kernel/2015-October/002402.html
> No, this isn't a good starting point (please look at Stephen's comment, which still apply).
>
> My suggestion would be to use or extend the cpufreq-dt. I'm not sure that we can you use clk-bcm2835 or need a separate clock driver (via mailbox) which changes the VPU clock.
>
> @Eric: What's your opinion?
>
> The advantages of this approach:
> - no new binding required
> - in good case no cpufreq driver is necessary
> - chance of acceptance in mainline is very high
>
> AFAIK there is only a need to register the cpufreq-dt within the bcm2835 plaform code and provide the operation points.
>
> Best regards
> Stefan
>
>> Thank you for details.
>>
>>
I tried to do a quick test and looked at cpufreq-dt driver. It seems to 
require an explicitly set CPU clock but there is nothing set in the 
existing device trees like bcm2837.dtsi.