linux-kernel - Re: [PATCH v10 1/7] interconnect: Add generic on-chip interconnect API

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Message-ID: <82026d31-39e8-08f1-761b-c0b3ccf8ce20@linaro.org>
Date:   Wed, 28 Nov 2018 20:18:04 +0200
From:   Georgi Djakov <georgi.djakov@...aro.org>
To:     Joe Perches <joe@...ches.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,
        mark.rutland@....com, lorenzo.pieralisi@....com,
        abailon@...libre.com, maxime.ripard@...tlin.com, arnd@...db.de,
        thierry.reding@...il.com, ksitaraman@...dia.com,
        sanjayc@...dia.com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v10 1/7] interconnect: Add generic on-chip interconnect
 API

Hi Joe,

On 11/27/18 20:35, Joe Perches wrote:
> On Tue, 2018-11-27 at 20:03 +0200, 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.
> 
> trivial notes:
> 
>> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> []
>> +static int apply_constraints(struct icc_path *path)
>> +{
>> +	struct icc_node *next, *prev = NULL;
>> +	int ret = -EINVAL;
>> +	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;
>> +
>> +		/* set the constraints */
>> +		ret = p->set(prev, next);
>> +		if (ret)
>> +			goto out;
>> +	}
>> +out:
>> +	return ret;
>> +}
> 
> The use of ", prev = next" appears somewhat tricky code.
> Perhaps move the assignment of prev to the bottom of the loop.
> Perhaps the temporary p assignment isn't useful either.
> 
>> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)
>> +{
> []
>> +	ret = apply_constraints(path);
>> +	if (ret)
>> +		pr_debug("interconnect: error applying constraints (%d)", ret);
> 
> Ideally all pr_<foo> formats should end in '\n'
> 
>> +static struct icc_node *icc_node_create_nolock(int id)
>> +{
>> +	struct icc_node *node;
>> +
>> +	/* check if node already exists */
>> +	node = node_find(id);
>> +	if (node)
>> +		goto out;
>> +
>> +	node = kzalloc(sizeof(*node), GFP_KERNEL);
>> +	if (!node) {
>> +		node = ERR_PTR(-ENOMEM);
>> +		goto out;
> 
> Generally, this code appears to overly rely on goto when
> direct returns could be more readable.
> 
>> +	}
>> +
>> +	id = idr_alloc(&icc_idr, node, id, id + 1, GFP_KERNEL);
>> +	if (WARN(id < 0, "couldn't get idr")) {
> 
> This seems to unnecessarily hide the id < 0 test in a WARN
> 
> Why is this a WARN and not a simpler
> 	if (id < 0) {
> 		[ pr_err(...); or WARN(1, ...); ]
> 
>> +		kfree(node);
>> +		node = ERR_PTR(id);
>> +		goto out;
>> +	}
>> +
>> +	node->id = id;
>> +
>> +out:
>> +	return node;
>> +}

Thank you for helping to improve the code. The above suggestions make it 
cleaner indeed.

> []
>> diff --git a/include/linux/interconnect.h b/include/linux/interconnect.h
> []
>> +/* macros for converting to icc units */
>> +#define bps_to_icc(x)	(1)
>> +#define kBps_to_icc(x)	(x)
> []
>> +#define MBps_to_icc(x)	(x * 1000)
>> +#define GBps_to_icc(x)	(x * 1000 * 1000)
>> +#define kbps_to_icc(x)	(x / 8 + ((x) % 8 ? 1 : 0))
>> +#define Mbps_to_icc(x)	(x * 1000 / 8 )
>> +#define Gbps_to_icc(x)	(x * 1000 * 1000 / 8)
> 
> The last 5 macros should parenthesize x

Oops.. obviously i forgot to run checkpatch --strict. Will fix!

BR,
Georgi