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SubjectRe: [PATCH v3 09/10] drivers: qcom: rpmh: add support for batch RPMH request
Date
Quoting Lina Iyer (2018-03-08 14:55:40)
> On Thu, Mar 08 2018 at 14:59 -0700, Stephen Boyd wrote:
> >Quoting Lina Iyer (2018-03-02 08:43:16)
> >> @@ -343,6 +346,146 @@ int rpmh_write(struct rpmh_client *rc, enum rpmh_state state,
> >> }
> >> EXPORT_SYMBOL(rpmh_write);
> >>
> >> +static int cache_batch(struct rpmh_client *rc,
> >> + struct rpmh_request **rpm_msg, int count)
> >> +{
> >> + struct rpmh_ctrlr *rpm = rc->ctrlr;
> >> + unsigned long flags;
> >> + int ret = 0;
> >> + int index = 0;
> >> + int i;
> >> +
> >> + spin_lock_irqsave(&rpm->lock, flags);
> >> + while (rpm->batch_cache[index])
> >
> >If batch_cache is full.
> >And if adjacent memory has bits set....
> >
> >This loop can go forever?
> >
> >Please add bounds.
> >
> How so? The if() below will ensure that it will not exceed bounds.

Right, the if below will make sure we don't run off the end, but unless
rpm->batch_cache has a sentinel at the end we can't guarantee we won't
run off the end of the array and into some other portion of memory that
also has a bit set in a word. And then we may read into some unallocated
space. Or maybe I missed something.

>
> >> + index++;
> >> + if (index + count >= 2 * RPMH_MAX_REQ_IN_BATCH) {
> >> + ret = -ENOMEM;
> >> + goto fail;
> >> + }
> >> +
> >> + for (i = 0; i < count; i++)
> >> + rpm->batch_cache[index + i] = rpm_msg[i];
> >> +fail:
> >> + spin_unlock_irqrestore(&rpm->lock, flags);
> >> +
> >> + return ret;
> >> +}
> >> +
>
> >> + * @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 mailbox 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(struct rpmh_client *rc, enum rpmh_state state,
> >> + struct tcs_cmd *cmd, int *n)
> >
> >I'm lost why n is a pointer, and cmd is not a double pointer if n stays
> >as a pointer. Are there clients calling this API with a contiguous chunk
> >of commands but then they want to break that chunk up into many
> >requests?
> >
> That is correct. Clients want to provide a big buffer that this API will
> break it up into requests specified in *n.

Is that for bus scaling?

> >> + return PTR_ERR(rpm_msg[i]);
> >> + }
> >> + cmd += n[i];
> >> + }
> >> +
> >> + /* Send if Active and wait for the whole set to complete */
> >> + if (state == RPMH_ACTIVE_ONLY_STATE) {
> >> + might_sleep();
> >> + atomic_set(&wait_count, count);
> >
> >Aha, here's the wait counter.
> >
> :)
> I am removing it from the earlier patch and introducing the wait_count
> here. Not bad as I though.

Thanks!

>
> >> + for (i = 0; i < count; i++) {
> >> + rpm_msg[i]->completion = &compl;
> >> + rpm_msg[i]->wait_count = &wait_count;
> >
> >But then we just assign the same count and completion to each rpm_msg?
> >Why? Can't we just put the completion on the final one and have the
> >completion called there?
> >
> The order of the responses is not gauranteed to be sequential and in the
> order it was sent. So we have to do this.

OK! That is sad.

>
> >> + /* Bypass caching and write to mailbox directly */
> >> + ret = rpmh_rsc_send_data(rc->ctrlr->drv,
> >> + &rpm_msg[i]->msg);
> >> + if (ret < 0) {
> >> + pr_err(
> >> + "Error(%d) sending RPMH message addr=0x%x\n",
> >> + ret, rpm_msg[i]->msg.payload[0].addr);
> >> + break;
> >> + }
> >> + }
> >> + /* For those unsent requests, spoof tx_done */
> >
> >Why? Comments shouldn't say what the code is doing, but explain why
> >things don't make sense.
> >
> Will remove..
>

Oh, I was hoping for more details, not less.

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