Hi Kay, On Sun, 5 Jul 2009 22:19:46 +0200, Kay Sievers wrote: > On Sat, Jul 4, 2009 at 19:14, Jean Delvare<khali@xxxxxxxxxxxx> wrote: > > On Mon, 4 May 2009 14:40:36 +0200, Kay Sievers wrote: > > >> (The less difference between classes and buses the better. It is wrong > >> to have two types of subsystems, doing almost the same thing. One > >> could argue that it could be useful inside the kernel, which it isn't, > >> I think, but exporting them to userspace was definitely the wrong > >> thing.) > > > > I finally took a stab at this. The resulting patch is below. I have > > used device_type to differentiate between I2C clients and I2C adapters. > > Is this what you had in mind? > > Looks fine, by just looking at the patch. > > > It seems to work reasonably well, with the following issues remaining: > > > > * The change breaks at least sensors-detect and libsensors. I can > > easily modify them so that they work again, but we still have a > > compatibility issue. Is it possible to have a compatibility option > > that would add symbolic links from class/i2c-adapter/i2c-* to > > bus/i2c/devices/i2c-* for a couple years? > > Yeah, we can add that. I guess others will need that too, if we > convert things from class to bus. How would that look like? Like a > device_add_class_compat_link(*dev, *class)? Yes. I'm not just sure what "class" would be exactly... either a "real" fake class, or a mere string representing the fake class name? > > * Now that i2c-core makes use of device_type, I tried to move the power > > management handling callbacks there from bus_type, to save a test in > > each function, however I found that the callback set is different > > between bus_type and device_type.pm. Why is it so? Is there a document > > explaining the difference? Is the whole world (including bus_type) > > eventually moving to dev_pm_ops? > > I think this is already removed in the current git tree, and all > should use dev_pm_ops, yes. In which git tree? In Linus' tree, struct bus_type definitely doesn't use dev_pm_ops yet. > > * When i2c-adapters were class devices, virtual ones (for example > > i2c-stub) appeared in sysfs as devices/virtual/i2c-adapter/i2c-*, > > which made sense and seemed safe. Now that I have turned them into > > bus devices, virtual ones appear in sysfs as devices/i2c-* directly, > > which looks dirty and could result in collisions someday. What should > > be done about this? I wanted to use virtual_device_parent() but it is > > internal to the driver core at the moment, and doesn't even exist if > > CONFIG_SYSFS_DEPRECATED=y. > > Yeah, we just need to apply the /sys/devices/virtual logic to bus > devices too, it's currently limited to class devices, because there > was no bus device so far who needed this, but should be an easy > change. It will probably have do be a little different, as it is valid to register a device without a parent, to have it appear at the root (actually 1st level) of the device tree. So we'll need a way to differentiate between this case and the virtual device case. I admit I am a little surprised that I am the first person asking for virtual bus devices, especially given how you like to repeat that i2c was doing things differently from the rest of the world so far and I am merely changing i2c to fit in the common model. > > I would be grateful if you can advise on any of the above points. > > If you decide to do it that way, you would need the driver core to be able: > - to create a link from an otherwise empty "struct class" to an > existing bus-device > - put bus devices without a parent into the /sys/devices/virtual logic > right? Let me know, I can look into that, if you need that. Yes, this is a good summary of my needs. With some room for discussion on both points: * Do we need an actually struct class for each fake class, or just a class name? * Do we want to put virtual devices in devices/virtual directly, or do we want separate namespaces? But these are details which can be solved on the way, and I have no strong opinion about them anyway. Thanks, -- 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
