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. If every devboard manufacturer did a similar thing and had USB power always enabled by default without any need to configure anything (with or without the possibility to switch it off if necessary), then we would have a much easier job with generic device-independent bootable SD card installer images for Allwinner boards: http://lists.denx.de/pipermail/u-boot/2015-January/202306.html "USB host ports use dedicated pins and only enabling/disabling power can be device specific. The missing USB power can be solved by using a powered USB hub, which is not very convenient, but still a workable solution." -- 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