linux-kernel - Re: [PATCH] PM: EM: Force device drivers to provide power in uW

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Date: Thu, 14 Mar 2024 11:57:48 +0000
From: Lukasz Luba <lukasz.luba@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 poshao.chen@...iatek.com
Subject: Re: [PATCH] PM: EM: Force device drivers to provide power in uW



On 3/13/24 19:49, Rafael J. Wysocki wrote:
> On Fri, Mar 8, 2024 at 1:31 PM Lukasz Luba <lukasz.luba@....com> wrote:
>>
>> The EM only supports power in uW. Make sure that it is not possible to
>> register some downstream driver which doesn't provide power in uW.
>> The only exception is artificial EM, but that EM is ignored by the rest of
>> kernel frameworks (thermal, powercap, etc).
>>
>> Reported-by: PoShao Chen <poshao.chen@...iatek.com>
>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>> ---
>>
>> Hi all,
>>
>> The was an issue reported recently that the EM could be used with
>> not aligned drivers which provide milli-Watts. This patch prevents such
>> drivers to register EM (although there are no such in upstream).
>>
>> Regards,
>> Lukasz
>>
>>   kernel/power/energy_model.c | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
>> index b686ac0345bd9..9e1c9aa399ea9 100644
>> --- a/kernel/power/energy_model.c
>> +++ b/kernel/power/energy_model.c
>> @@ -612,6 +612,17 @@ int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
>>          else if (cb->get_cost)
>>                  flags |= EM_PERF_DOMAIN_ARTIFICIAL;
>>
>> +       /*
>> +        * EM only supports uW (exception is artificial EM).
>> +        * Therefore, check and force the drivers to provide
>> +        * power in uW.
>> +        */
>> +       if (!microwatts && !(flags & EM_PERF_DOMAIN_ARTIFICIAL)) {
>> +               dev_err(dev, "EM: only supports uW power values\n");
>> +               ret = -EINVAL;
>> +               goto unlock;
>> +       }
>> +
>>          ret = em_create_pd(dev, nr_states, cb, cpus, flags);
>>          if (ret)
>>                  goto unlock;
>> --
> 
> Applied as 6.9-rc material, thanks!

Thank you Rafael!