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Subject: Re: [PATCH v8 09/10] drivers: qcom: rpmh: add support for batch RPMH
 request
To:     Doug Anderson <dianders@chromium.org>,
        Lina Iyer <ilina@codeaurora.org>
Cc:     Andy Gross <andy.gross@linaro.org>,
        David Brown <david.brown@linaro.org>,
        linux-arm-msm@vger.kernel.org,
        "open list:ARM/QUALCOMM SUPPORT" <linux-soc@vger.kernel.org>,
        Rajendra Nayak <rnayak@codeaurora.org>,
        msivasub@codeaurora.org, mkshah@codeaurora.org,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Evan Green <evgreen@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>
References: <20180509170159.29682-1-ilina@codeaurora.org>
 <20180509170159.29682-10-ilina@codeaurora.org>
 <CAD=FV=Xvi8V43+J9v-mosU5WUDQtabg8gUbrkn6SCoNEYFtjUQ@mail.gmail.com>
From:   Raju P L S S S N <rplsssn@codeaurora.org>
Message-ID: <bb2d3dfb-08be-de3e-c18f-616ee27fa2e9@codeaurora.org>
Date:   Wed, 23 May 2018 18:57:25 +0530
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Hi,

will reply on points other than what Lina has responded.

On 5/12/2018 1:49 AM, Doug Anderson wrote:
> Hi,
> 
> On Wed, May 9, 2018 at 10:01 AM, Lina Iyer <ilina@codeaurora.org> wrote:
>>   /**
>> @@ -77,12 +82,14 @@ struct rpmh_request {
>>    * @cache: the list of cached requests
>>    * @lock: synchronize access to the controller data
>>    * @dirty: was the cache updated since flush
>> + * @batch_cache: Cache sleep and wake requests sent as batch
>>    */
>>   struct rpmh_ctrlr {
>>          struct rsc_drv *drv;
>>          struct list_head cache;
>>          spinlock_t lock;
>>          bool dirty;
>> +       const struct rpmh_request *batch_cache[RPMH_MAX_BATCH_CACHE];
> 
> I'm pretty confused about why the "batch_cache" is separate from the
> normal cache.  As far as I can tell the purpose of the two is the same
> but you have two totally separate code paths and data structures.
> 
> 
>>   };
>>
>>   static struct rpmh_ctrlr rpmh_rsc[RPMH_MAX_CTRLR];
>> @@ -133,6 +140,7 @@ void rpmh_tx_done(const struct tcs_request *msg, int r)
>>          struct rpmh_request *rpm_msg = container_of(msg, struct rpmh_request,
>>                                                      msg);
>>          struct completion *compl = rpm_msg->completion;
>> +       atomic_t *wc = rpm_msg->wait_count;
>>
>>          rpm_msg->err = r;
>>
>> @@ -143,8 +151,13 @@ void rpmh_tx_done(const struct tcs_request *msg, int r)
>>          kfree(rpm_msg->free);
>>
>>          /* Signal the blocking thread we are done */
>> -       if (compl)
>> -               complete(compl);
>> +       if (!compl)
>> +               return;
> 
> The comment above this "if" block no longer applies to the line next
> to it after your patch.  ...but below I suggest you get rid of
> "wait_count", so maybe this part of the patch will go away.
> 
> 
>> +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 (index < RPMH_MAX_BATCH_CACHE && ctrlr->batch_cache[index])
>> +               index++;
>> +       if (index + count >= RPMH_MAX_BATCH_CACHE) {
>> +               ret = -ENOMEM;
>> +               goto fail;
>> +       }
>> +
>> +       for (i = 0; i < count; i++)
>> +               ctrlr->batch_cache[index + i] = rpm_msg[i];
>> +fail:
> 
> Nit: this label is for both failure and normal exit, so call it "exit".
> 
> 
>> +       spin_unlock_irqrestore(&ctrlr->lock, flags);
>> +
>> +       return ret;
>> +}
> 
> As part of my overall confusion about why the batch cache is different
> than the normal one: for the normal use case you still call
> rpmh_rsc_write_ctrl_data() for things you put in your cache, but you
> don't for the batch cache.  I still haven't totally figured out what
> rpmh_rsc_write_ctrl_data() does, but it seems strange that you don't
> do it for the batch cache but you do for the other one.
> 
> 
>> +/**
>> + * 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.
>> + *
>> + * Write a request to the RSC controller without caching. If the request
>> + * state is ACTIVE, then the requests are treated as completion request
>> + * and sent to the controller immediately. The function waits until all the
>> + * commands are complete. If the request was to SLEEP or WAKE_ONLY, then the
>> + * request is sent as fire-n-forget and no ack is expected.
>> + *
>> + * May sleep. Do not call from atomic contexts for ACTIVE_ONLY requests.
>> + */
>> +int rpmh_write_batch(const struct device *dev, enum rpmh_state state,
>> +                    const struct tcs_cmd *cmd, u32 *n)
>> +{
>> +       struct rpmh_request *rpm_msg[RPMH_MAX_REQ_IN_BATCH] = { NULL };
>> +       DECLARE_COMPLETION_ONSTACK(compl);
>> +       atomic_t wait_count = ATOMIC_INIT(0);
>> +       struct rpmh_ctrlr *ctrlr = get_rpmh_ctrlr(dev);
>> +       int count = 0;
>> +       int ret, i;
>> +
>> +       if (IS_ERR(ctrlr) || !cmd || !n)
>> +               return -EINVAL;
>> +
>> +       while (n[count++] > 0)
>> +               ;
>> +       count--;
>> +       if (!count || count > RPMH_MAX_REQ_IN_BATCH)
>> +               return -EINVAL;
>> +
>> +       for (i = 0; i < count; i++) {
>> +               rpm_msg[i] = __get_rpmh_msg_async(state, cmd, n[i]);
>> +               if (IS_ERR_OR_NULL(rpm_msg[i])) {
> 
> Just "IS_ERR".  It's never NULL.
> ...also add a i-- somewhere in here or you're going to be kfree()ing
> your error value, aren't you?

Sure. Will make change in next patch.

> 
> 
>> +                       ret = PTR_ERR(rpm_msg[i]);
>> +                       for (; i >= 0; i--)
>> +                               kfree(rpm_msg[i]->free);
>> +                       return ret;
>> +               }
>> +               cmd += n[i];
>> +       }
>> +
>> +       if (state != RPMH_ACTIVE_ONLY_STATE)
>> +               return cache_batch(ctrlr, rpm_msg, count);
> 
> Don't you need to free rpm_msg items in this case?
> 
> 
>> +
>> +       atomic_set(&wait_count, count);
>> +
>> +       for (i = 0; i < count; i++) {
>> +               rpm_msg[i]->completion = &compl;
>> +               rpm_msg[i]->wait_count = &wait_count;
>> +               ret = rpmh_rsc_send_data(ctrlr->drv, &rpm_msg[i]->msg);
>> +               if (ret) {
>> +                       int j;
>> +
>> +                       pr_err("Error(%d) sending RPMH message addr=%#x\n",
>> +                              ret, rpm_msg[i]->msg.cmds[0].addr);
>> +                       for (j = i; j < count; j++)
>> +                               rpmh_tx_done(&rpm_msg[j]->msg, ret);
> 
> You're just using rpmh_tx_done() to free memory?  Note that you'll
> probably do your error handling in this function a favor if you rename
> __get_rpmh_msg_async() to __fill_rpmh_msg() and remove the memory
> allocation from there.  Then you can do one big allocation of the
> whole array in rpmh_write_batch() and then you'll only have one free
> at the end...
> 
> 
> 
>> +                       break;
> 
> "break" seems wrong here.  You'll end up waiting for the completion,
> then I guess timing out, then returning -ETIMEDOUT?

As the loop above break runs for remaining count, completion will be 
notified so there will not be waiting.

Thanks,
Raju

> 
> 
>> +               }
>> +       }
>> +
>> +       ret = wait_for_completion_timeout(&compl, RPMH_TIMEOUT_MS);
> 
> The "wait_count" abstraction is confusing and I believe it's not
> needed.  I think you can remove it and change the above to this
> (untested) code:
> 
> time_left = RPMH_TIMEOUT_MS;
> for (i = 0; i < count; i++) {
>    time_left = wait_for_completion_timeout(&compl, time_left);
>    if (!time_left)
>      return -ETIMEDOUT;
> }
> 
> ...specifically completions are additive, so just wait "count" times
> and then the reader doesn't need to learn your new wait_count
> abstraction and try to reason about it.
> 
> ...and, actually, I argue in other replies that this should't use a
> timeout, so even cleaner:
> 
> for (i = 0; i < count; i++)
>    wait_for_completion(&compl);
> 
> 
> Once you do that, you can also get rid of the need to pre-count "n",
> so all your loops turn into:
> 
> for (i = 0; n[i]; i++)
> 
> 
> I suppose you might want to get rid of "RPMH_MAX_REQ_IN_BATCH" and
> dynamically allocate your array too, but that seems sane.  As per
> above it seems like you should just dynamically allocate a whole array
> of "struct rpmh_request" items at once anyway.
> 
> ---
> 
>> +       return (ret > 0) ? 0 : -ETIMEDOUT;
>> +
>> +}
>> +EXPORT_SYMBOL(rpmh_write_batch);
> 
> Perhaps an even simpler thing than taking all my advice above: can't
> you just add a optional completion to rpmh_write_async()?  That would
> just be stuffed into rpm_msg.
> 
> Now your batch code would just be a bunch of calls to
> rpmh_write_async() with an equal number of wait_for_completion() calls
> at the end.  Is there a reason that wouldn't work?  You'd get rid of
> _a lot_ of code.
> 
> 
> -Doug
>