Date:   Fri, 11 May 2018 13:19:02 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Lina Iyer <ilina@...eaurora.org>
Cc:     Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        linux-arm-msm@...r.kernel.org,
        "open list:ARM/QUALCOMM SUPPORT" <linux-soc@...r.kernel.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Evan Green <evgreen@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>, rplsssn@...eaurora.org
Subject: Re: [PATCH v8 09/10] drivers: qcom: rpmh: add support for batch RPMH request

Hi,

On Wed, May 9, 2018 at 10:01 AM, Lina Iyer <ilina@...eaurora.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?


> +                       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?


> +               }
> +       }
> +
> +       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

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