On Tue, 13 Nov 2012 22:24:50 +0100, Alexander Holler wrote: > Am 13.11.2012 22:08, schrieb Jean Delvare: > > It probes in the sense "check if a device is present", not in the sense > > "check if the device there is really what the user told me." So very > > easy to get wrong. Plus there is no universal probe method on I2C, > > i2c_new_probed_device() uses a default heuristic which may not only > > fail to detect a device's presence, but may even heavily confuse the > > device in question. Usage of i2c_new_probed_device() should be limited > > to very specific cases. > > I know about that too. But I prefer such a probe instead of doing it > without an probe. Just try what happens if you add e.g. an pcf8563 (or > ds1307) which is not available. The driver doesn't care and you will > find an /dev/rtcN afterwards in your system. So probing is imho better > than not. Question is, what will you do the day someone wants to instantiate a device for which the default probing mechanism doesn't work? Plus you don't address the main issues. Your syntax gives you no way to support two i2c-tiny-usb adapters with different chips at a specific address. The sysfs interface supports such a setup. Also instantiating the wrong devices is worse than instating a device that doesn't exist at all. So the use of i2c_new_probed_device() here will randomly help in a limited number of cases and randomly be problematic in others. Hard to justify... > > I am not questioning the quality of your code, I did not even look at > > it. I'm questioning the pertinence of adding yet another way to > > instantiate i2c devices when we already have 4 which made everybody > > else happy for the past 3 years AFAIK. > > As said, currently there is no way to do that whithout either patching > the kernel or working in userspace. And a RTC is just an example for a > device you really want before userspace starts (but imho a very good). I am not familiar with RTC constraints. What is so important about it that it can't wait for user-space? It'll have to wait for the USB and I2C stacks to initialize anyway, so it won't be available at the very early stages of the boot. -- Jean Delvare -- 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
