linux-kernel - Re: [PATCH v6 1/8] interconnect: Add generic on-chip interconnect API

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Date:   Fri, 20 Jul 2018 17:33:10 +0300
From:   Georgi Djakov <georgi.djakov@...aro.org>
To:     Alexandre Bailon <abailon@...libre.com>
Cc:     linux-pm@...r.kernel.org, gregkh@...uxfoundation.org,
        rjw@...ysocki.net, robh+dt@...nel.org, mturquette@...libre.com,
        khilman@...libre.com, vincent.guittot@...aro.org,
        skannan@...eaurora.org, bjorn.andersson@...aro.org,
        amit.kucheria@...aro.org, seansw@....qualcomm.com,
        daidavid1@...eaurora.org, evgreen@...omium.org, mka@...omium.org,
        mark.rutland@....com, lorenzo.pieralisi@....com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v6 1/8] interconnect: Add generic on-chip interconnect API

Hi Alexandre,

On 07/11/2018 07:21 PM, Alexandre Bailon wrote:
> On 07/09/2018 05:50 PM, Georgi Djakov wrote:
>> This patch introduces a new API to get requirements and configure the
>> interconnect buses across the entire chipset to fit with the current
>> demand.
>>
>> The API is using a consumer/provider-based model, where the providers are
>> the interconnect buses and the consumers could be various drivers.
>> The consumers request interconnect resources (path) between endpoints and
>> set the desired constraints on this data flow path. The providers receive
>> requests from consumers and aggregate these requests for all master-slave
>> pairs on that path. Then the providers configure each participating in the
>> topology node according to the requested data flow path, physical links and
>> constraints. The topology could be complicated and multi-tiered and is SoC
>> specific.
>>
>> Signed-off-by: Georgi Djakov <georgi.djakov@...aro.org>
>> ---

[..]

>> +static int apply_constraints(struct icc_path *path)
>> +{
>> +	struct icc_node *next, *prev = NULL;
>> +	int ret;
>> +	int i;
>> +
>> +	for (i = 0; i < path->num_nodes; i++, prev = next) {
>> +		struct icc_provider *p;
>> +
>> +		next = path->reqs[i].node;
>> +		/*
>> +		 * Both endpoints should be valid master-slave pairs of the
>> +		 * same interconnect provider that will be configured.
>> +		 */
>> +		if (!prev || next->provider != prev->provider)
>> +			continue;
>> +
>> +		p = next->provider;
>> +
>> +		aggregate_provider(p);
>> +
>> +		/* set the constraints */
>> +		ret = p->set(prev, next, p->avg_bw, p->peak_bw);
> I'm confuse here.
> In path_init(), the first reqs' node takes the node.
> But here, this same element is assigned to prev, which is used as src by
> set(). For me this looks like prev and next have been inverted.

Ok, right. Will change the order of reqs to go from the source to the
destination.

Thanks,
Georgi

>> +		if (ret)
>> +			goto out;
>> +	}
>> +out:
>> +	return ret;
>> +}
>> +