Re: [PATCH v8 09/10] drivers: qcom: rpmh: add support for batch RPMH request

From: Raju P L S S S N
Date: Wed May 23 2018 - 08:34:14 EST

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@xxxxxxxxxxxxxx> 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