On Mon, 5 Oct 2015 14:49:49 +0200 Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote: > On Mon, Oct 05, 2015 at 08:39:40AM +0300, Siarhei Siamashka wrote: > > On Mon, 5 Oct 2015 09:55:28 +0800 > > Chen-Yu Tsai <wens@xxxxxxxx> wrote: > > > > > On Mon, Oct 5, 2015 at 2:58 AM, Siarhei Siamashka > > > <siarhei.siamashka@xxxxxxxxx> wrote: > > > > The pcDuino1 board does not use any power switches at all for its > > > > two USB host ports and the VBUS pins are always connected to 5V. > > > > > > > > The pcDuino2 board uses the RT9701GB power switch for its single > > > > USB host port, but the USB_EN pin (PD2) is pulled up with a 10K > > > > resistor. So that the USB power is still enabled by default even > > > > if nobody bothers to configure the PD2 pin or runs the pcDuino1 > > > > firmware. > > > > > > Seems like it would be better if you had a regulator controlled > > > by PD2. At least can shut down VBUS power when it wants to? > > > > That's a good question. > > > > Describing the regulator controlled by PD2 in the dts file is surely > > the right solution for pcDuino2 boards. But in the case of using this > > dts for pcDuino1, the kernel would think that it can shut down VBUS > > power, while in fact this is not true. > > I do agree that this is the right solution for the pcduino1, but it's > definitely not the right one for the pcduino 2 then. > > Declaring this as a regulator isn't just meant for the USB to be > working, it's also meant so that it keeps working. If the pin is not > claimed by anyone, the userspace and / or some other driver, will > actually be able to grab that pin and do whatever it wants with it, > effectively fiddling with the VBUS supply behind the USB driver's > back. OK. That's a very good point. > It also allows to disable the regulator if VBUS isn't going to be > used, for example because the driver has not be compiled in, or that > it's actually a module that might (or might not) be loaded later. > > Finally, it also allows to keep track of who consumes what amount of > power in the system, which is a nice plus. > > > The RT9701GB switch also provides the current limiting feature in > > addition to the ability to enable/disable the VBUS power. Probably > > this was a real reason why it was added to the board. > > > > Everything boils down to the question whether we want to have a > > common dts file for pcDuino1 and pcDuino2 or decide to split them. > > You don't have to split them, if this is really the only difference, > just create a new dts for the pcduino2 that includes the first one, > and add the supply there. Well, we get two dts files instead of one as the end result. If "split" is not a good description, then I should have probably used a different word for it. I don't mind having separate dts files for pcDuino1 and pcDuino2. What are we going to do with testing on pcDuino1? I only have pcDuino2 hardware myself. -- Best regards, Siarhei Siamashka -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
