linux-kernel - Re: [PATCH 1/2] Revert "drivers: qcom: rpmh-rsc: Use rcuidle tracepoints for rpmh"

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Date:   Sat, 22 Aug 2020 21:51:40 +0530
From:   Maulik Shah <mkshah@...eaurora.org>
To:     Stephen Boyd <swboyd@...omium.org>, agross@...nel.org,
        bjorn.andersson@...aro.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        ulf.hansson@...aro.org, dianders@...omium.org,
        rnayak@...eaurora.org, ilina@...eaurora.org, lsrao@...eaurora.org,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH 1/2] Revert "drivers: qcom: rpmh-rsc: Use rcuidle
 tracepoints for rpmh"

Hi,

On 8/19/2020 11:34 PM, Stephen Boyd wrote:
> Quoting Maulik Shah (2020-08-19 03:07:49)
>> This change was done based on an test results of unmerged series of
>> adding RSC power domain and using .power_off callback of genpd to
>> invoke rpmh_flush().
> Perhaps:
>
> Commit efde2659b0fe ("drivers: qcom: rpmh-rsc: Use rcuidle tracepoints
> for rpmh") was written to fix a bug seen in an unmerged series that
> implemented a struct generic_pm_domain::power_off() callback calling
> rpmh_flush(). See stack trace below.
Sure i will update in v2.
>
>>       Call trace:
>>        dump_backtrace+0x0/0x174
>>        show_stack+0x20/0x2c
>>        dump_stack+0xc8/0x124
>>        lockdep_rcu_suspicious+0xe4/0x104
>>        __tcs_buffer_write+0x230/0x2d0
>>        rpmh_rsc_write_ctrl_data+0x210/0x270
>>        rpmh_flush+0x84/0x24c
>>        rpmh_domain_power_off+0x78/0x98
>>        _genpd_power_off+0x40/0xc0
>>        genpd_power_off+0x168/0x208
>>
>> Later the final merged solution is to use CPU PM notification to invoke
>> rpmh_flush() and .power_off callback of genpd is not implemented in the
>> driver.
> I'd also add:
>
> CPU PM notifiers are run with RCU enabled/watching (see cpu_pm_notify()
> and how it calls rcu_irq_enter_irqson() before calling the notifiers).
Sure i will update in v2.
>
>> Remove this change since RCU will not be idle during CPU PM notifications
>> hence not required to use _rcuidle tracepoint. Using _rcuidle tracepoint
>> prevented rpmh driver to be loadable module as these are not exported
>> symbols.
>>
>> This reverts commit efde2659b0fe835732047357b2902cca14f054d9.
>>
>> Cc: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>> Cc: John Stultz <john.stultz@...aro.org>
>> Cc: Stephen Rothwell <sfr@...b.auug.org.au>
>> Signed-off-by: Maulik Shah <mkshah@...eaurora.org>
>> ---
> Otherwise
>
> Reviewed-by: Stephen Boyd <swboyd@...omium.org>

Thanks for the review.

Thanks,
Maulik

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