On Fri, Jan 09, 2004 at 04:56:12PM -0700, Matthew Mastracci wrote: > >But adapters are not on the i2c bus. They are the "root" of the i2c > >bus. I2C adapters live as devices on other busses (PCI, platform, etc.) > > I'm modelling this after the usb sysfs entry. The usb adapters > themselves appear in /sys/bus/usb/devices: That is because those "usbX" devices _are_ real USB devices. They are the USB root hub, which lives in the silicon inside the USB controller. The kernel sees them as a real USB device, and they talk USB to the kernel. I2C adapters are not like that. > >What exactly is the problem that HAL can't see the devices in the place > >where they are in the sysfs tree? > > Without this patch, the device only appears in two places: > > * under the class directory with class "i2c-adapter", and This is why that class directory was created. In order that userspace can find all of the i2c adapters. > * under the root devices tree in its respective pci path. > > If you contrast this with the usb controllers, they appear in three places: > > * under the class directory with class "usb_host", > * under the root devices tree in its repective pci path, and > * under the /sys/bus/usb directory Again, the USB root hubs are a different type of device, you can't compare the two, sorry. > HAL uses libsysfs, which parses the contents of the various bus/ > directories to determine the appropriate bus for the given subdevices > beneath each device. It assumes that for each valid device directory > directory in the /sys/devices/ tree, there is an entry in one of the bus > directories. > > Since the I2C-n directories don't appear in any of the bus directories, > libsysfs can only print "unknown" bus for them and they can't be > appropriately placed within the HAL tree. But i2c adapters _are not_ on the i2c bus. They are the "bridge device" between say the PCI bus and the i2c bus. They are really just a PCI device, and so that's where they are in the tree. > I had assumed that since the I2C adapters are similar in function to the > usb_host devices, they should appear in the same place. Nope, apples and oranges. > If this is not the case, should the usb hosts be under the PCI bus tree > as well? In that case, should the I2C adapters be there too? USB hosts do show up in /sys/class/usb_hosts/ just like the i2c adapters do :) Hope this helps, greg k-h
