From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sudeep Holla Subject: Re: [PATCH v9 2/8] dt-bindings: Introduce interconnect binding Date: Wed, 10 Oct 2018 16:02:24 +0100 Message-ID: <20181010150224.GA3583@e107155-lin> References: <20180831140151.13972-1-georgi.djakov@linaro.org> <20180831140151.13972-3-georgi.djakov@linaro.org> <20180925180215.GA12435@bogus> <20180926144830.GB25838@e107155-lin> <20181002111758.GC1086@e107155-lin> <20181003093346.GA12570@e107155-lin> <0a276103-15fb-807c-5379-1a35de789290@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <0a276103-15fb-807c-5379-1a35de789290@codeaurora.org> Sender: linux-kernel-owner@vger.kernel.org To: Saravana Kannan Cc: Georgi Djakov , Rob Herring , 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 List-Id: linux-arm-msm@vger.kernel.org On Wed, Oct 03, 2018 at 11:06:45AM -0700, Saravana Kannan wrote: > > > On 10/03/2018 02:33 AM, Sudeep Holla wrote: > > 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. > > > What you are asking would be an ideal case, but this is not an ideal world. Agreed. > There are tons of constraints for each chip vendor. Saying you can't mix and > match makes perfect the enemy of the good. We can have endless debate on that. > Adding FW support for A and B might make them optimal. OK... > But adding support for X might not be possible for > multiple real world constraints (chip area, cost, time to market, etc). but is not a good design though. If f/w blindly changes DVFS for X based on OS request, then there's possibility for clkscrew kind of exploits still though moving A/B to f/w was to avoid it. The chances are low but not zero. > Saying "either do it all or do nothing" is going to hold back a lot progress > that can come in increments. Heck, we do the same thing in the kernel. We'll > add basic simple features first and then improve on them. Why is it suddenly > frowned up if a FW/HW follows the same approach? I'll just have to agree to > disagree with you on this view point. > I agree on adding basic and then improve on that policy. But it's not fair to compare this mix-'n'-match approach to that. Sorry but I disagree with the comparison here. -- Regards, Sudeep From mboxrd@z Thu Jan 1 00:00:00 1970 From: sudeep.holla@arm.com (Sudeep Holla) Date: Wed, 10 Oct 2018 16:02:24 +0100 Subject: [PATCH v9 2/8] dt-bindings: Introduce interconnect binding In-Reply-To: <0a276103-15fb-807c-5379-1a35de789290@codeaurora.org> References: <20180831140151.13972-1-georgi.djakov@linaro.org> <20180831140151.13972-3-georgi.djakov@linaro.org> <20180925180215.GA12435@bogus> <20180926144830.GB25838@e107155-lin> <20181002111758.GC1086@e107155-lin> <20181003093346.GA12570@e107155-lin> <0a276103-15fb-807c-5379-1a35de789290@codeaurora.org> Message-ID: <20181010150224.GA3583@e107155-lin> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Oct 03, 2018 at 11:06:45AM -0700, Saravana Kannan wrote: > > > On 10/03/2018 02:33 AM, Sudeep Holla wrote: > > 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. > > > What you are asking would be an ideal case, but this is not an ideal world. Agreed. > There are tons of constraints for each chip vendor. Saying you can't mix and > match makes perfect the enemy of the good. We can have endless debate on that. > Adding FW support for A and B might make them optimal. OK... > But adding support for X might not be possible for > multiple real world constraints (chip area, cost, time to market, etc). but is not a good design though. If f/w blindly changes DVFS for X based on OS request, then there's possibility for clkscrew kind of exploits still though moving A/B to f/w was to avoid it. The chances are low but not zero. > Saying "either do it all or do nothing" is going to hold back a lot progress > that can come in increments. Heck, we do the same thing in the kernel. We'll > add basic simple features first and then improve on them. Why is it suddenly > frowned up if a FW/HW follows the same approach? I'll just have to agree to > disagree with you on this view point. > I agree on adding basic and then improve on that policy. But it's not fair to compare this mix-'n'-match approach to that. Sorry but I disagree with the comparison here. -- Regards, Sudeep