mainline kernel: cpufreq for bcm2835
ssuloev at orpaltech.com
Mon Apr 2 14:15:48 PDT 2018
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 .
>>> 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
>>>  - https://github.com/lategoodbye/rpi-zero/issues
>> 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 ?
> 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
>> 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.
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