From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthias Kaehlcke Subject: Re: [PATCH v4 4/4] regulator: Prevent falling too fast Date: Tue, 13 Dec 2016 15:14:52 -0800 Message-ID: <20161213231452.GB96889@google.com> References: <20160915143945.GJ27974@sirena.org.uk> <20160915180223.GE62872@google.com> <20160916163253.GA10189@sirena.org.uk> <20160924184133.seh6v6eayt7hwgue@sirena.org.uk> <20161028181521.ywzmow6bgndfotq3@sirena.org.uk> <20161212211502.GA96889@google.com> <20161213171904.ohsxc3xhscdinctt@sirena.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Doug Anderson Cc: Mark Brown , Liam Girdwood , Brian Norris , Javier Martinez Canillas , Rob Herring , Mark Rutland , "linux-kernel@vger.kernel.org" , "devicetree@vger.kernel.org" List-Id: devicetree@vger.kernel.org Hi, El Tue, Dec 13, 2016 at 12:00:32PM -0800 Doug Anderson ha dit: > On Tue, Dec 13, 2016 at 9:19 AM, Mark Brown wrote: > > On Mon, Dec 12, 2016 at 01:15:02PM -0800, Matthias Kaehlcke wrote: > >> El Fri, Oct 28, 2016 at 07:15:21PM +0100 Mark Brown ha dit: > >> > On Mon, Sep 26, 2016 at 10:41:59AM -0700, Doug Anderson wrote: > > > >> > What you're describing to me is a discrete DCDC that has an input > >> > voltage that sets the output voltage which happens to be set with a PWM. > > > >> I experimented a bit with this. Besides the question of how to model > >> the passives I wonder how the two regulators would interact. The > >> correct thing seems to be to specify the input regulator as a supply > >> of the DCDC. dcdc->set_voltage breaks down a voltage transition into > > > > No, not unless the prior descriptions of the hardware have been wildly > > inaccurate - my understanding had been that the DCDC was a normal DCDC > > with an analogue input intended to be biased to set the output voltage > > (presumably in terms of a full rail supply) and that the PWM had been > > connected to this analogue input. If the PWM is supplying the DCDC then > > the hardware design just seems bizzare, I can't see how this would even > > work. > > Looking at one schematic, the discrete BUCK for at least one of the > rails is TPS65261RHBR, which appears to be described at > . Data sheet appears to be at > . > > As you can see from the datasheet ("Adjusting the Output Voltage" > section), it is intended that you stuff a resistor to make a voltage > divider and that's how you select the output voltage. In our case the > PWM interacts here and allows you to make a more dynamic output > voltage. I've always thought about the input to the "FB" pin as > making an input voltage, but I guess it's not terribly simple since > the voltage divider ends up dividing between ground and the output > voltage. I also had put my mind on seeing the output of the PWM circuitry as an input voltage, but technically it isn't a supply of the buck regulator. It seems we could consider it a "control voltage" instead and thus avoid the recursive lock acquisition. Matthias