linux-kernel - Re: [PATCH v9 2/8] dt-bindings: Introduce interconnect binding

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Date:   Wed, 3 Oct 2018 10:33:46 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Saravana Kannan <skannan@...eaurora.org>
Cc:     Georgi Djakov <georgi.djakov@...aro.org>,
        Rob Herring <robh@...nel.org>, linux-pm@...r.kernel.org,
        gregkh@...uxfoundation.org, rjw@...ysocki.net,
        mturquette@...libre.com, khilman@...libre.com,
        vincent.guittot@...aro.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,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH v9 2/8] dt-bindings: Introduce interconnect binding

On Tue, Oct 02, 2018 at 11:56:56AM -0700, Saravana Kannan wrote:
> 
> On 10/02/2018 04:17 AM, Sudeep Holla wrote:

[...]

> > Yes, I do understand I have made the same point multiple time and it's
> > intentional. We need to get the fragmented f/w support story fixed.
> > Different ARM vendors are doing different things in f/w and ARM sees the
> > same fragmentation story as before. We have come up with new specification
> > and my annoying multiple emails are just to constantly remind the same.
> > 
> > I do understand we have existing implementations to consider, but fixing
> > the functionality in arbitrary way is not a good design and it better
> > to get them fixed for future.
> 
> I believe the fragmentation you are referring to is  in the
> interface/communication protocol. I see the benefit of standardizing that as
> long as the standard actually turns out to be good. But that's completely
> separate from what the FW can/can't do. Asking to standardize what the FW
> can/can't do doesn't seem realistic as each chip vendor will have different
> priorities - power, performance, cost, chip area, etc. It's the conflation
> of these separate topics that doesn't help IMHO.

I agree on interface/communication protocol fragmentation and firmware
can implement whatever the vendor wish. What I was also referring was
the mix-n-match approach which should be avoided.

e.g. Device A and B's PM is managed completely by firmware using OSPM hints
Suppose Device X's PM is dependent on Device A and B, in which case it's
simpler and cleaner to leave Device X PM to firmware. Reading the state
of A and B and using that as hint for X is just overhead which firmware
can manage better. That was my main concern here: A=CPU and B=some other
device and X is inter-connect to which A and B are connected.

If CPU OPPs are obtained from f/w and this inter-connect from DT, mapping
then is a mess and that's what I was concerned. I am sorry if that's not
the scenario here, I may have mistaken then.

--
Regards,
Sudeep