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

From: Sudeep Holla <sudeep.holla@arm.com>
To: Saravana Kannan <skannan@codeaurora.org>
Cc: Georgi Djakov <georgi.djakov@linaro.org>,
	Rob Herring <robh@kernel.org>,
	linux-pm@vger.kernel.org, gregkh@linuxfoundation.org,
	rjw@rjwysocki.net, mturquette@baylibre.com, khilman@baylibre.com,
	vincent.guittot@linaro.org, bjorn.andersson@linaro.org,
	amit.kucheria@linaro.org, seansw@qti.qualcomm.com,
	daidavid1@codeaurora.org, evgreen@chromium.org,
	mark.rutland@arm.com, lorenzo.pieralisi@arm.com,
	abailon@baylibre.com, maxime.ripard@bootlin.com, arnd@arndb.de,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-arm-msm@vger.kernel.org,
	Sudeep Holla <sudeep.holla@arm.com>
Subject: Re: [PATCH v9 2/8] dt-bindings: Introduce interconnect binding
Date: Wed, 3 Oct 2018 10:33:46 +0100	[thread overview]
Message-ID: <20181003093346.GA12570@e107155-lin> (raw)
In-Reply-To: <c17450ce-fc25-e792-b91b-51106f032542@codeaurora.org>

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