From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nishanth Menon Subject: Re: [PATCH V4 1/3] OPP: Redefine bindings to overcome shortcomings Date: Wed, 13 May 2015 11:14:07 -0500 Message-ID: <5553784F.7040905@ti.com> References: <554FFFA3.1060801@ti.com> <20150512051633.GB32300@linux> <555224A2.7000308@ti.com> <20150513050559.GE28858@linux> <55536719.5050208@ti.com> <20150513151652.GX2761@sirena.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150513151652.GX2761@sirena.org.uk> Sender: linux-pm-owner@vger.kernel.org To: Mark Brown Cc: Viresh Kumar , Rafael Wysocki , rob.herring@linaro.org, arnd.bergmann@linaro.org, mike.turquette@linaro.org, sboyd@codeaurora.org, linaro-kernel@lists.linaro.org, linux-pm@vger.kernel.org, grant.likely@linaro.org, olof@lixom.net, Sudeep.Holla@arm.com, devicetree@vger.kernel.org, viswanath.puttagunta@linaro.org, l.stach@pengutronix.de, thomas.petazzoni@free-electrons.com, linux-arm-kernel@lists.infradead.org, ta.omasab@gmail.com, kesavan.abhilash@gmail.com, khilman@linaro.org, santosh.shilimkar@oracle.com List-Id: devicetree@vger.kernel.org On 05/13/2015 10:16 AM, Mark Brown wrote: > On Wed, May 13, 2015 at 10:00:41AM -0500, Nishanth Menon wrote: > >> What I dont see in the thread, and the point I raised here, why have >> nominal/typical voltage at all? min<->max should be sufficient, >> correct? If the device cannot function at min, then it should not be >> documented as part of valid range at all. > > Going for the minimum specified voltage is asking for trouble with > regard to tolerances and so on, see also your concern about process > corners. If the electrical engineers specify things as X +/- Y the > most conservative thing to do is to try to hit X rather than going > straight for the limits. I've had the same debate with my company's SoC designers as well on various occasions as well. At least for the SoCs I deal with, X +/- Y range specification involves PMIC/Board variations, where X is the least voltage that is attempted to be set on PMIC, X-Y is the min voltage allowed at the SoC ball, due to SMPS noise/IRDrop and other board specific behavior. I am not saying all SoC vendors do specifications the same way, but our interest from device tree description is the operating voltage range for the device that we can control on the PMIC. if setting (X-Y) is not stable voltage for the device, then it should not be stated in the description. To illustrate: What does it mean for a driver using regulator API? Attempt X <-> (X+Y), if that fails (example PMIC SMPS max < X), try (X-Y)<->(X)? If yes, then we do expect (X-Y)<->(X+Y) should be stable for all operating conditions for the device, correct? If this is is not stable at (X-Y), then we have a wrong specification for the device for claiming X +/- Y is a valid range for the device. -- Regards, Nishanth Menon From mboxrd@z Thu Jan 1 00:00:00 1970 From: nm@ti.com (Nishanth Menon) Date: Wed, 13 May 2015 11:14:07 -0500 Subject: [PATCH V4 1/3] OPP: Redefine bindings to overcome shortcomings In-Reply-To: <20150513151652.GX2761@sirena.org.uk> References: <554FFFA3.1060801@ti.com> <20150512051633.GB32300@linux> <555224A2.7000308@ti.com> <20150513050559.GE28858@linux> <55536719.5050208@ti.com> <20150513151652.GX2761@sirena.org.uk> Message-ID: <5553784F.7040905@ti.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 05/13/2015 10:16 AM, Mark Brown wrote: > On Wed, May 13, 2015 at 10:00:41AM -0500, Nishanth Menon wrote: > >> What I dont see in the thread, and the point I raised here, why have >> nominal/typical voltage at all? min<->max should be sufficient, >> correct? If the device cannot function at min, then it should not be >> documented as part of valid range at all. > > Going for the minimum specified voltage is asking for trouble with > regard to tolerances and so on, see also your concern about process > corners. If the electrical engineers specify things as X +/- Y the > most conservative thing to do is to try to hit X rather than going > straight for the limits. I've had the same debate with my company's SoC designers as well on various occasions as well. At least for the SoCs I deal with, X +/- Y range specification involves PMIC/Board variations, where X is the least voltage that is attempted to be set on PMIC, X-Y is the min voltage allowed at the SoC ball, due to SMPS noise/IRDrop and other board specific behavior. I am not saying all SoC vendors do specifications the same way, but our interest from device tree description is the operating voltage range for the device that we can control on the PMIC. if setting (X-Y) is not stable voltage for the device, then it should not be stated in the description. To illustrate: What does it mean for a driver using regulator API? Attempt X <-> (X+Y), if that fails (example PMIC SMPS max < X), try (X-Y)<->(X)? If yes, then we do expect (X-Y)<->(X+Y) should be stable for all operating conditions for the device, correct? If this is is not stable at (X-Y), then we have a wrong specification for the device for claiming X +/- Y is a valid range for the device. -- Regards, Nishanth Menon