On Mon, 5 Oct 2015 08:39:40 +0300 Siarhei Siamashka <siarhei.siamashka@xxxxxxxxx> 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. > > 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. > Based on the schematics comparison, there do not seem to be any > substantial differences between these boards if we ignore the PD2 > pin altogether. LinkSprite says that "Ubuntu images are same for > both pcDuino1 and pcDuino2" at their website: > http://www.linksprite.com/?page_id=809 > > And I actually like their decision to have the PD2 pin pulled-up. I'm not sure if everyone would like this, but the following trick works. If we configure the PD2 pin as input with pull-down on the SoC side and read it, then it still reads as 1 on pcDuino2. Which means that the pull-up is apparently stronger (by how much and whether this is really reliable is another question). It should read as 0 on pcDuino1 and we might use this to detect the board type at runtime. Still it is probably an overkill for just this really minor thing :-) -- 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
