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Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:44886) by pandora.armlinux.org.uk with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1k06xh-00037t-BM; Mon, 27 Jul 2020 18:30:53 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1k06xf-0003pn-Gq; Mon, 27 Jul 2020 18:30:51 +0100 Date: Mon, 27 Jul 2020 18:30:51 +0100 From: Russell King - ARM Linux admin To: Alexandre Belloni Subject: Re: [PATCH v2 1/3] dt-bindings: rtc: pcf8523: add DSM pm option for battery switch-over Message-ID: <20200727173051.GM1551@shell.armlinux.org.uk> References: <20200720112401.4620-2-miguelborgesdefreitas@gmail.com> <20200723174905.GA596242@bogus> <20200723195755.GV3428@piout.net> <20200727094553.GH1551@shell.armlinux.org.uk> <20200727144938.GC239143@piout.net> <20200727152439.GK1551@shell.armlinux.org.uk> <20200727154104.GE239143@piout.net> <20200727154335.GL1551@shell.armlinux.org.uk> <20200727161632.GF239143@piout.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200727161632.GF239143@piout.net> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200727_133102_933850_F5E6FFBA X-CRM114-Status: GOOD ( 23.63 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Rob Herring , Baruch Siach , Sascha Hauer , a.zummo@towertech.it, Fabio Estevam , Sascha Hauer , Jon Nettleton , Linux Kernel Mailing List , devicetree , NXP Linux Team , Miguel Borges de Freitas , Shawn Guo , linux-arm-kernel Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Jul 27, 2020 at 06:16:32PM +0200, Alexandre Belloni wrote: > On 27/07/2020 17:55:50+0200, Jon Nettleton wrote: > > > So, can we please have that discussion, it is pertinent to this patch. > > > > > > > Thinking about this some more, I believe whether or not an IOCTL > > interface is in the works or needed is irrelevant. This patch > > describes the hardware and how it is designed and the topic of > > discussion is if we need a simple boolean state, or if we need > > something that could be used to support dynamic configuration in the > > future. I would rather make this decision now rather than keep > > tacking on boolean config options, or revisit a bunch of device-tree > > changes. > > Something that would describe the hardware is a property telling whether > the filter is present on VDD, not a property selecting DSM. The driver > can then chose to avoid standard mode when needed. Whether DSM needs to be enabled or not is _not_ just a function of whether there is a filter present or not. The requirement in the data sheet is that when the VDD supply drops below 2.5V, it does not fall more than 0.7V/ms. That can be achieved many different ways, not only by adding a resistive filter to the VDD supply to the RTC. It could also be achieved via the design of the power supply - for example, having a large enough reservoir capacitor to ensure under all loads that the VDD supply will not fall faster than 0.7V/ms. There are many ways to meet this requirement. Adding a DT property to indicate whether the filter is present or not is definitely not the right approach. Should we also add properties for every possible solution to this problem. vdd-has-filter; psu-has-large-capacitors; ... etc ... -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last! _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel