Re: [linux-sunxi] [PATCH 1/3] ARM: dts: sun4i: Allow to use the PH6 pin for GPIO on pcDuino1/2
On Mon, 5 Oct 2015 08:58:53 +0300 Siarhei Siamashka wrote: > On Mon, 5 Oct 2015 08:39:40 +0300 > Siarhei Siamashka wrote: > > > On Mon, 5 Oct 2015 09:55:28 +0800 > > Chen-Yu Tsai wrote: > > > > > On Mon, Oct 5, 2015 at 2:58 AM, Siarhei Siamashka > > > 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 :-) I few more details about this. I have actually measured the voltage with/without pull-down on the SoC side (which competes with the 10K pull-up resistor on the PCB) and the results are the following. The voltage drops from 3.306V to 3.187V on one board and from 3.325V to 3.204V on another. Based on these numbers, we can in estimate pull-down resistors used for GPIO inside of the A10 SoC as something like ~270K Ohm. As such, it looks like we can do reliable runtime detection of pcDuino1 and pcDuino2 variants by probing this PD2 pin. The most appropriate place to do the runtime detection is probably the board type selection stub (sunxi-bootsetup), run as the initial part of a Linux distribution installer. We are perfectly fine having separate dts files for the pcDuino1/pcDuino2 boards and the kernel does not need to become more complicated. Probing for pull-up and pull-down resistors on the PCB can be generalized beyond just PD2 and used to further narrow down the selection of compatible boards (sunxi-bootsetup currently only considers the SoC type, DRAM size and DRAM bus width for this). Additional very interesting observation is that the reference Allwinner schematics and Cubieboard/Cubietruck boards use 510K pull-down resistor for the USB power switches. With 270K pull-up by the SoC and 510K pull-down by a resistor on the PCB, the resulting voltage is going to be around ~2.2V, which should be enough to be interpreted as digital 1. And indeed, a quick test shows that if we just configure either PH3 or PH6 pin as input with pull-up, then the corresponding USB port gets powered up on the Cubieboard :-) There are two important consequences: * As far as generic device independent code is concerned, we can reasonably safely enable USB power on the Cubieboard, Cubietruck and other device, which did not deviate from the reference Allwinner schematics and used 510K pull-down resistors. Configuring pins for input can't possibly do much harm (if any at all). * By doing run-time checks, we can see the difference between the boards using 10K pull-down resistors (OLIMEX boards) and the boards using 510K pull-down resistors (CubieTech boards). -- Best regards, Siarhei Siamashka -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [linux-sunxi] [PATCH 1/3] ARM: dts: sun4i: Allow to use the PH6 pin for GPIO on pcDuino1/2
On Mon, 5 Oct 2015 14:49:49 +0200 Maxime Ripard 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 wrote: > > > > > On Mon, Oct 5, 2015 at 2:58 AM, Siarhei Siamashka > > > 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [linux-sunxi] [PATCH 1/3] ARM: dts: sun4i: Allow to use the PH6 pin for GPIO on pcDuino1/2
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 wrote: > > > On Mon, Oct 5, 2015 at 2:58 AM, Siarhei Siamashka > > 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. 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. Thanks! Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com signature.asc Description: Digital signature
Re: [linux-sunxi] [PATCH 1/3] ARM: dts: sun4i: Allow to use the PH6 pin for GPIO on pcDuino1/2
On Mon, 5 Oct 2015 08:39:40 +0300 Siarhei Siamashka wrote: > On Mon, 5 Oct 2015 09:55:28 +0800 > Chen-Yu Tsai wrote: > > > On Mon, Oct 5, 2015 at 2:58 AM, Siarhei Siamashka > > 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [linux-sunxi] [PATCH 1/3] ARM: dts: sun4i: Allow to use the PH6 pin for GPIO on pcDuino1/2
On Mon, 5 Oct 2015 09:55:28 +0800 Chen-Yu Tsai wrote: > On Mon, Oct 5, 2015 at 2:58 AM, Siarhei Siamashka > 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [linux-sunxi] [PATCH 1/3] ARM: dts: sun4i: Allow to use the PH6 pin for GPIO on pcDuino1/2
On Mon, Oct 5, 2015 at 2:58 AM, Siarhei Siamashka 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? ChenYu > The current dts file unnecessarily meddles with the PH3 and PH6 > pins. But the PH6 pin is available on the J11 expansion header > and may have a better use for other purposes. This patch fixes > the problem and now the PH6 pin can be used with the GPIO sysfs > interface. Tested on a pcDuino2 board and confirmed the voltage > on the PH6 pin with a multimeter: > > echo 230 > /sys/class/gpio/export > echo "out" > /sys/class/gpio/gpio230/direction > echo 0 > /sys/class/gpio/gpio230/value > echo 1 > /sys/class/gpio/gpio230/value > > USB still works as expected too. > > Signed-off-by: Siarhei Siamashka > --- > arch/arm/boot/dts/sun4i-a10-pcduino.dts | 10 -- > 1 file changed, 10 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
