On Wed, Jan 19, 2011 at 02:23:41PM +0100, Arvid Brodin wrote: > Hello, > > How do I make my platform device a character device that > can be handled by udev? Have you read the Linux Device Drivers book about this very topic? If not, I suggest you do so. > Background: > > I've written a driver for a very simple platform device (a jumper > connected to an input pin on the processor). Today I can read the status > of the pin through a driver attribute file in sysfs at: > > /sys/devices/platform/msel/ > > As a learning experience I want to get udev to detect this device and > create a character device file under /dev for it, that I could read to > get the pin status. If I understand correctly, udev looks for files > named "dev" in sysfs, which contains the major and minor device numbers > which udev use to create the device node. > > From the kernel code it seems that ((struct platform_device *) > my_platform_device)->dev->devt would have to be set to contain the major > & minor device numbers when the device is created for a "dev" file to > appear, which is not possible in this case since the device is > registered in board setup code where it seems wrong to get device > numbers by calling call alloc_chrdev_region() (right?). > > I found a few previous questions about this same problem in these > kernelnewbies threads: > > http://www.mail-archive.com/kernelnewbies@xxxxxxxxxxxx/msg08461.html > http://www.mail-archive.com/kernelnewbies@xxxxxxxxxxxx/msg06807.html > > Using that info, and looking at the hpet driver code, I initialised a > struct miscdevice and called misc_register(). This gives me a > /sys/class/misc/msel_chrdev/ folder with the required dev and > uevent files. udev also picks up this and creates the corresponding file > in /dev. Great. > Is this the correct way to do this? One "device" for the hardware and > one or more "devices" for the userland interface(s)? Yes. But you might want to rethink a char device for your user interface, as it doesn't sound like it fits very well. What about the GPIO interface instead? thanks, greg k-h _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
