linux-kernel - Re: [PATCH v4 1/7] interconnect: Add generic on-chip interconnect API

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Date:   Wed, 6 Jun 2018 18:06:05 -0700
From:   Evan Green <evgreen@...omium.org>
To:     georgi.djakov@...aro.org
Cc:     linux-pm@...r.kernel.org, gregkh@...uxfoundation.org,
        rjw@...ysocki.net, robh+dt@...nel.org,
        Michael Turquette <mturquette@...libre.com>,
        khilman@...libre.com, Vincent Guittot <vincent.guittot@...aro.org>,
        Saravana Kannan <skannan@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        amit.kucheria@...aro.org, seansw@....qualcomm.com,
        davidai@...cinc.com, 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 v4 1/7] interconnect: Add generic on-chip interconnect API

On Wed, Jun 6, 2018 at 11:09 AM Georgi Djakov <georgi.djakov@...aro.org> wrote:
>
> Hi Evan,
>
> On 06/06/2018 05:59 PM, Georgi Djakov wrote:
> >>> +
> >>> +/**
> >>> + * icc_node_create() - create a node
> >>> + * @id: node id
> >>> + *
> >>> + * Return: icc_node pointer on success, or ERR_PTR() on error
> >>> + */
> >>> +struct icc_node *icc_node_create(int id)
> >>> +{
> >>> +       struct icc_node *node;
> >>> +
> >>> +       /* check if node already exists */
> >>> +       node = node_find(id);
> >>> +       if (node)
> >>> +               return node;
> >>
> >> This is probably going to do more harm than good once icc_node_delete comes
> >> in, since it almost certainly indicates a programmer error or ID collision,
> >> and will likely result in a double free. We should probably fail with
> >> EEXIST instead.
> >
> > In the current approach we create the nodes one by one, and the linked
> > nodes are created when they are referenced. The other way around would
> > be to create first all the nodes and then populate the links to avoid
> > the "chicken and egg" problem.
> >
>
> Just to elaborate a bit more on that: We can't actually register all the
> nodes in advance, as we might have multiple interconnect providers
> probing in different order. Each provider may have nodes linking to
> nodes belonging to other providers (not probed yet). That's why we
> create the nodes on the first reference and then, when the actual
> provider driver is probed, the rest of the node data is filled.
>

Ah ok, the extra explanation helped a lot. This makes sense to me. Thanks.
-Evan