linux-kernel - Re: [PATCH 1/2] soc: qcom: rpmhpd: Use corner in power

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Date:   Mon, 5 Jul 2021 11:10:58 +0530
From:   Rajendra Nayak <rnayak@...eaurora.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] soc: qcom: rpmhpd: Use corner in power_off



On 7/5/2021 10:36 AM, Bjorn Andersson wrote:
> On Sun, Jul 4, 2021 at 11:27 PM Rajendra Nayak <rnayak@...eaurora.org> wrote:
>>
>>
>>
>> On 7/3/2021 6:24 AM, Bjorn Andersson wrote:
>>> rpmhpd_aggregate_corner() takes a corner as parameter, but in
>>> rpmhpd_power_off() the code requests the level of the first corner
>>> instead.
>>>
>>> In all (known) current cases the first corner has level 0, so this
>>> change should be a nop, but in case that there's a power domain with a
>>> non-zero lowest level this makes sure that rpmhpd_power_off() actually
>>> requests the lowest level - which is the closest to "power off" we can
>>> get.
>>>
>>> While touching the code, also skip the unnecessary zero-initialization
>>> of "ret".
>>>
>>> Fixes: 279b7e8a62cc ("soc: qcom: rpmhpd: Add RPMh power domain driver")
>>> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
>>> ---
>>>    drivers/soc/qcom/rpmhpd.c | 5 ++---
>>>    1 file changed, 2 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/soc/qcom/rpmhpd.c b/drivers/soc/qcom/rpmhpd.c
>>> index 2daa17ba54a3..fa209b479ab3 100644
>>> --- a/drivers/soc/qcom/rpmhpd.c
>>> +++ b/drivers/soc/qcom/rpmhpd.c
>>> @@ -403,12 +403,11 @@ static int rpmhpd_power_on(struct generic_pm_domain *domain)
>>>    static int rpmhpd_power_off(struct generic_pm_domain *domain)
>>>    {
>>>        struct rpmhpd *pd = domain_to_rpmhpd(domain);
>>> -     int ret = 0;
>>> +     int ret;
>>>
>>>        mutex_lock(&rpmhpd_lock);
>>>
>>> -     ret = rpmhpd_aggregate_corner(pd, pd->level[0]);
>>> -
>>> +     ret = rpmhpd_aggregate_corner(pd, 0);
>>
>> This won't work for cases where pd->level[0] != 0, rpmh would just ignore this and keep the
>> resource at whatever corner it was previously at.
>> (unless command DB tells you a 0 is 'valid' for a resource, sending a 0 is a nop)
>> The right thing to do is to send in whatever command DB tells you is the lowest level that's valid,
>> which is pd->level[0].
>>
> 
> I'm afraid this doesn't make sense to me.
> 
> In rpmh_power_on() if cmd-db tells us that we have [0, 64, ...] and we
> request 64 we rpmhpd_aggregate_corner(pd, 1); but in power off, if
> cmd-db would provide [64, ...] we would end up sending
> rpmhpd_aggregate_corner(pd, 64);
> So in power_on we request the corner (i.e. index in the array provided
> in cmd-db) and in power-off the same function takes the level?

ah that's right, I did not read the commit log properly and got confused.
Looks like this bug existed from the day this driver for merged :/, thanks
for catching it.
Does it make sense to also mark this fix for stable?

> 
> Can you please help me understand what the actual number we're
> supposed to send to the RPMh is? Is it numbers in the range [0-15] or
> is it numbers such as {0, 64, 128, ...}?
> 
> Afaict it's the prior (i.e. [0-15]), as this is what we currently do
> in both power_on and set_performance_state, and it happens to be what
> we send in power_off as long as the first level from cmd-db is 0.
> 
> Regards,
> Bjorn
> 
>>
>>>        if (!ret)
>>>                pd->enabled = false;
>>>
>>>
>>
>> --
>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
>> of Code Aurora Forum, hosted by The Linux Foundation

-- 
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation