Hello, Am Mittwoch, 22. August 2012, 16:04:39 schrieb Feng Tang: > > Why use a fixed one? Give the driver (and maybe every i2c bus driver) a parameter which sets the base bus number it should use. > > E.g. i2c-eg20t.base-bus-num=2 so it will register the bus numbers starting from 2. If this parameter is unset. It would use the first free one, thus simply using i2c_add_adapter. > > The reason we need a fixed number is it is easier for platform code > which needs to register dozens of i2c devices to different controllers > with i2c_register_board_info, and they need provide a bus number for > each i2c device, this _binding_ info is not detectable but have to > be fixed. Yes, I'm aware of that. With "Why use a fixed one?" I meant why hard-code it into the driver. I should be changeable. Because this is/was not possible in general to use i2c_register_board_info, so we used an echo to /sys/bus/i2c/devices/i2c-0/new_device or /sys/bus/i2c/devices/i2c-1/new_device. > Yes, your module parameter "base-bus-num" sounds like a plan too, > at the cost of some extra setting in the kernel cmdline. And I'm fine > with all solutions as long as I can get a _fixed_ bus number so that > I can easily write the platform config code (I guess this is same > for device tree, and even ACPI 5.0) i2c_add_numbered_adapter only works reliably if only using a single driver. If you are using several, especially if one uses dynamic bus numbers, you're kinda screwed. So, not very driver can add busses starting at bus number 0. I guess using an Intel Atom (i2c-isch) with an eg20t is not that uncommon, so you'll end up using 2 drivers where each one should have a fixed number. Some mechanism like udev for renaming ethernet or block devices is needed here. Regards, Alexander -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
