linux-kernel - Re: [PATCH v6 09/10] drivers: qcom: rpmh: add support for batch RPMH request

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Date:   Fri, 27 Apr 2018 10:24:08 -0600
From:   Lina Iyer <ilina@...eaurora.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     andy.gross@...aro.org, david.brown@...aro.org,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        rnayak@...eaurora.org, bjorn.andersson@...aro.org,
        linux-kernel@...r.kernel.org, sboyd@...nel.org,
        evgreen@...omium.org, dianders@...omium.org
Subject: Re: [PATCH v6 09/10] drivers: qcom: rpmh: add support for batch RPMH
 request

On Wed, Apr 25 2018 at 17:41 -0600, Matthias Kaehlcke wrote:
>On Thu, Apr 19, 2018 at 04:16:34PM -0600, Lina Iyer 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>
>> ---
>>
>> Changes in v6:
>> 	- replace rpmh_client with device *
>> Changes in v4:
>> 	- reorganize rpmh_write_batch()
>> 	- introduce wait_count here, instead of patch#4
>> ---
>>  drivers/soc/qcom/rpmh.c | 155 +++++++++++++++++++++++++++++++++++++++-
>>  include/soc/qcom/rpmh.h |   8 +++
>>  2 files changed, 161 insertions(+), 2 deletions(-)
>>

><snip>
>
>> +static int cache_batch(struct rpmh_ctrlr *ctrlr,
>> +		       struct rpmh_request **rpm_msg, int count)
>> +{
>> +	unsigned long flags;
>> +	int ret = 0;
>> +	int index = 0;
>> +	int i;
>> +
>> +	spin_lock_irqsave(&ctrlr->lock, flags);
>> +	while (ctrlr->batch_cache[index])
>> +		index++;
>
>This will access memory beyond 'batch_cache' when the cache is full.
>
Ok. Will check for index.

><snip>
>
>> +static void invalidate_batch(struct rpmh_ctrlr *ctrlr)
>> +{
>> +	unsigned long flags;
>> +	int index = 0;
>> +	int i;
>> +
>> +	spin_lock_irqsave(&ctrlr->lock, flags);
>> +	while (ctrlr->batch_cache[index])
>> +		index++;
>
>Same as above. Also, why loop twice?
>
Good idea. Will fix.

>> +	for (i = 0; i < index; i++) {
>> +		kfree(ctrlr->batch_cache[i]->free);
>> +		ctrlr->batch_cache[i] = NULL;
>> +	}
>
><snip>
>
>> +/**
>> + * rpmh_write_batch: Write multiple sets of RPMH commands and wait for the
>> + * batch to finish.
>> + *
>> + * @dev: the device making the request
>> + * @state: Active/sleep set
>> + * @cmd: The payload data
>> + * @n: The array of count of elements in each batch, 0 terminated.
>
>nit: in this driver 'n' is usually associated with the command offset
>within a TCS. Since it isn't an overly descriptive name it may already
>cost the reader a while to commit that to his/her memory, and now
>we are overloading 'n' with a different meaning (I also noticed this in
>another patch of this series, but didn't comment).
>
Sure, will change the variable name here.

>>  	/*
>>  	 * Nobody else should be calling this function other than system PM,,
>                                                                            ~
>Remove extra comma.
OK.

Thanks,
Lina