On 19 September 2016 at 13:23, Jan Kandziora <j...@gmx.de> wrote: > Am 19.09.2016 um 10:42 schrieb Colin Law: >> I have been trying >> to get to grips with device tree and (on pi with raspbian jessie) in >> /boot/overlays/README it says >> >> "Device Tree makes it possible >> to support many hardware configurations with a single kernel and without the >> need to explicitly load or blacklist kernel modules." >> >> which I think means that it should not be necessary to use modprobe >> w1-gpio or to put the module in /etc/modules. >> > This is a misunderstanding. > > If you don't modprobe the module, someone else has to do. It depends on > your udev setup whether udev does it for you. The kernel doesn't load > modules automatically just because a device is listed in the loaded > device tree.
Are you sure about that? https://www.raspberrypi.org/documentation/configuration/device-tree.md says, in section 3.1, "With a Device Tree, the kernel will automatically search for and load modules that support the indicated, enabled devices. As a result, by creating an appropriate DT overlay for a device, you save users of the device from having to edit /etc/modules; all of the configuration goes in config.txt, and in the case of a HAT, even that step is unnecessary. Note, however, that layered modules such as i2c-dev still need to be loaded explicitly." > > Before device trees, hardware layout has been hardcoded in the driver > modules or have to be specified by module options. That's what is no > longer necessary. > >> ... >> Does this mean I can (should?) use >> dtoverlay=w1-gpio,gpiopin=4,pullup=y >> > Haven't checked yet. Technically it is possible to use the internal push > transistor of the GPIO port to act as a strong pullup. > > HOWEVER, you should use a series resistor outside the GPIO port then. > Because, overcurrent from shorting the Onewire too long may kill the > GPIO4 push transistor inside the BCM2835 SoC. I didn't realise there was a push transistor in the GPIO port. I haven't been able to find any information on this. Do you have any references/specs I can look up? If the push does work then presumably one can get away with a higher value of pullup on the data line. > >> and remove the modprobe command? >> > Check with lsmod whether the module gets loaded automatically by udev. I can confirm that using raspbian Jessie w1-gpio is loaded without using modprobe or putting it in /etc/modules Cheers Colin ------------------------------------------------------------------------------ _______________________________________________ Owfs-developers mailing list Owfs-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/owfs-developers
