linux-kernel - Re: [PATCH] opp: fix dev_pm_opp_set_rate for different frequency at the same opp level

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Date:   Wed, 17 Feb 2021 08:29:43 -0500
From:   Jonathan Marek <jonathan@...ek.ca>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linux-arm-msm@...r.kernel.org, Viresh Kumar <vireshk@...nel.org>,
        Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>,
        "open list:OPERATING PERFORMANCE POINTS (OPP)" 
        <linux-pm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] opp: fix dev_pm_opp_set_rate for different frequency at
 the same opp level

On 2/16/21 11:53 PM, Viresh Kumar wrote:
> On 16-02-21, 15:10, Jonathan Marek wrote:
>> There is not "nothing to do" when the opp is the same. The frequency can
>> be different from opp->rate.
> 
> I am sorry but I am not sure what are you trying to fix here and what exactly is
> broken here. Can you provide a usecase for your platform where this doesn't work
> like it used to ?
> 

The specific case is this opp table:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/qcom/sm8250.dtsi#n439

It does not define every possible clock frequency, it only defines the 
rates at which a higher rpmhpd level must be used. Which is the intended 
use of opp.

Your change broke this completely: the clock rate change can be silently 
ignored because the opp level is the same. In particular it breaks 
bluetooth for this platform.

>> Fixes: 81c4d8a3c414 ("opp: Keep track of currently programmed OPP")
>> Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
>> ---
>>   drivers/opp/core.c | 7 +++++--
>>   drivers/opp/opp.h  | 1 +
>>   2 files changed, 6 insertions(+), 2 deletions(-)
>