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!
