linux-kernel - Re: [PATCH v2 09/10] drivers: qcom: rpmh: add support for batch RPMH request

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Message-ID: <20180222170451.GB7098@codeaurora.org>
Date:   Thu, 22 Feb 2018 17:04:51 +0000
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 v2 09/10] drivers: qcom: rpmh: add support for batch RPMH
 request

On Wed, Feb 21 2018 at 23:25 +0000, Evan Green wrote:
>Hello Lina,
>
>On Thu, Feb 15, 2018 at 9:35 AM, Lina Iyer <ilina@...eaurora.org> wrote:
>> Platform drivers need make a lot of resource state requests at the same
>> time, say, at the start or end of an usecase. It can be quite
>> inefficient to send each request separately. Instead they can give the
>> RPMH library a batch of requests to be sent and wait on the whole
>> transaction to be complete.
>>
>> rpmh_write_batch() is a blocking call that can be used to send multiple
>> RPMH command sets. Each RPMH command set is set asynchronously and the
>> API blocks until all the command sets are complete and receive their
>> tx_done callbacks.
>>
>> Signed-off-by: Lina Iyer <ilina@...eaurora.org>
>> ---
>>  drivers/soc/qcom/rpmh.c | 150 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  include/soc/qcom/rpmh.h |   8 +++
>>  2 files changed, 158 insertions(+)
>>
>> diff --git a/drivers/soc/qcom/rpmh.c b/drivers/soc/qcom/rpmh.c
>> index dff4c46be3af..6f60bb9a4dfa 100644
>> --- a/drivers/soc/qcom/rpmh.c
>> +++ b/drivers/soc/qcom/rpmh.c
>[...]
>> @@ -394,6 +537,11 @@ int rpmh_flush(struct rpmh_client *rc)
>>         }
>>         spin_unlock_irqrestore(&rpm->lock, flags);
>>
>> +       /* First flush the cached batch requests */
>> +       ret = flush_batch(rc);
>> +       if (ret)
>> +               return ret;
>> +
>>         /*
>>          * Nobody else should be calling this function other than system PM,,
>>          * hence we can run without locks.
This comment and the comment in the header of this function.

>> @@ -438,6 +586,8 @@ int rpmh_invalidate(struct rpmh_client *rc)
>>         if (IS_ERR_OR_NULL(rc))
>>                 return -EINVAL;
>>
>> +       invalidate_batch(rc);
>> +
>
>Similarly to my comments in patch 7, aren't there races here with
>adding new elements? After flush_batch, but before invalidate_batch,
>somebody could call cache_batch, which would add new things on the end
>of the array. These new items would be clobbered by invalidate_batch,
>without having been flushed first.
>
Flush is a system PM function and is not called by drivers and is not
expected to run conncurrently with other threads using the RPMH library.

Thanks,
Lina