linux-kernel - Re: [PATCH v9 1/5] driver core: Find an existing link between two devices

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Date:   Wed, 14 Mar 2018 12:57:11 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Vivek Gautam <vivek.gautam@...eaurora.org>,
        Lukas Wunner <lukas@...ner.de>, Joerg Roedel <joro@...tes.org>,
        Rob Herring <robh+dt@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        devicetree@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will.deacon@....com>,
        Rob Clark <robdclark@...il.com>,
        Sricharan R <sricharan@...eaurora.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Archit Taneja <architt@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v9 1/5] driver core: Find an existing link between two devices

On Wednesday, March 14, 2018 12:50:54 PM CET Tomasz Figa wrote:
> On Wed, Mar 14, 2018 at 8:12 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > On Tuesday, March 13, 2018 12:23:34 PM CET Tomasz Figa wrote:
> >> On Tue, Mar 13, 2018 at 7:34 PM, Vivek Gautam
> >> <vivek.gautam@...eaurora.org> wrote:
> >> > Hi Tomasz,
> >> >
> >> > On Tue, Mar 13, 2018 at 3:45 PM, Tomasz Figa <tfiga@...omium.org> wrote:
> >> >> Hi Vivek,
> >> >>
> >> >> Thanks for the patch.
> >> >>
> >> >> On Tue, Mar 13, 2018 at 5:55 PM, Vivek Gautam
> >> >> <vivek.gautam@...eaurora.org> wrote:
> >> >>> The lists managing the device-links can be traversed to
> >> >>> find the link between two devices. The device_link_add() APIs
> >> >>> does traverse these lists to check if there's already a link
> >> >>> setup between the two devices.
> >> >>> So, add a new APIs, device_link_find(), to find an existing
> >> >>> device link between two devices - suppliers and consumers.
> >> >>
> >> >> I'm wondering if this API would be useful for anything else that the
> >> >> problem we're trying to solve with deleting links without storing them
> >> >> anywhere. Perhaps a device_link_del_dev(consumer, supplier) would be a
> >> >> better alternative?
> >> >
> >> > Yea, that sounds simpler i think. Will add this API instead of
> >> > find_link(). Thanks.
> >>
> >> Perhaps let's wait for a moment to see if there are other opinions. :)
> >>
> >> Rafael, Lucas, any thoughts?
> >
> > It is not clear to me what the device_link_del_dev(consumer, supplier) would do.
> 
> It would delete a link between consumer and supplier.

If there's one I suppose.

I'm wondering if you are somehow trying to address the same problem as the
device links reference counting patch from Lukas that has been queued up for 4.17
already.

Thanks,
Rafael