linux-kernel - Re: [PATCH v3 07/10] drivers: qcom: rpmh: cache sleep/wake state requests

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Date:   Tue, 6 Mar 2018 15:12:38 -0700
From:   Lina Iyer <ilina@...eaurora.org>
To:     Evan Green <evgreen@...omium.org>
Cc:     Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 07/10] drivers: qcom: rpmh: cache sleep/wake state
 requests

On Mon, Mar 05 2018 at 13:45 -0700, Evan Green wrote:
>Hi Lina,
>
>On Fri, Mar 2, 2018 at 8:43 AM, Lina Iyer <ilina@...eaurora.org> wrote:
>> Active state requests are sent immediately to the mailbox controller,
>> while sleep and wake state requests are cached in this driver to avoid
>> taxing the mailbox controller repeatedly. The cached values will be sent
>> to the controller when the rpmh_flush() is called.
>>
>> Generally, flushing is a system PM activity and may be called from the
>> system PM drivers when the system is entering suspend or deeper sleep
>> modes during cpuidle.
>>
>> Also allow invalidating the cached requests, so they may be re-populated
>> again.
>>
>> Signed-off-by: Lina Iyer <ilina@...eaurora.org>
>> ---
>>
>> Changes in v3:
>>         - Remove locking for flush function
>>         - Improve comments
>> ---
>>  drivers/soc/qcom/rpmh.c | 208 +++++++++++++++++++++++++++++++++++++++++++++++-
>>  include/soc/qcom/rpmh.h |  10 +++
>>  2 files changed, 217 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/soc/qcom/rpmh.c b/drivers/soc/qcom/rpmh.c
>> index d95ea3fa8b67..8a04009075b8 100644
>> --- a/drivers/soc/qcom/rpmh.c
>> +++ b/drivers/soc/qcom/rpmh.c
>[...]
>> +
>> +/**
>> + * rpmh_invalidate: Invalidate all sleep and active sets
>> + * sets.
>> + *
>> + * @rc: The RPMh handle got from rpmh_get_dev_channel
>> + *
>> + * Invalidate the sleep and active values in the TCS blocks.
>> + */
>> +int rpmh_invalidate(struct rpmh_client *rc)
>> +{
>> +       struct rpmh_ctrlr *rpm = rc->ctrlr;
>> +       int ret;
>> +       unsigned long flags;
>> +
>> +       if (IS_ERR_OR_NULL(rc))
>> +               return -EINVAL;
>> +
>> +       spin_lock_irqsave(&rpm->lock, flags);
>> +       rpm->dirty = true;
>> +       spin_unlock_irqrestore(&rpm->lock, flags);
>
>Thanks for removing the locking from the flush path. I was hoping to
>see the locking removed around this statement as well. The way I
>understand it, all of the racy bits are attempting to set dirty to
>true, so you don't need a lock to protect multiple threads from
>setting the same value. The only time dirty is read or cleared is in
>the single-threaded PM path, so there are no potentially dangerous
>interactions.
>
Fair point. Will take care of it.

>If no one has any other comments on the series, then I don't need to
>hold everything up based on this one tweak alone. But if you end up
>spinning it again for other reasons, consider making this change as
>well.
>
Thanks,
Lina