On Wed, Oct 06, 2021 at 11:37:58AM +0200, Oliver Neukum wrote: > > On 05.10.21 21:59, Alan Stern wrote: > > On Tue, Oct 05, 2021 at 09:51:02AM -0700, Dmitry Torokhov wrote: > >> Hi Alan, > >> > >> On Tue, Oct 5, 2021 at 7:56 AM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > >>> As I understand it, the "removable" property refers specifically to > >>> the device's upstream link, not to whether _any_ of the links leading > >>> from the device to the computer could be removed. > >> No, that is not what it means. I'll cite our sysfs ABI: > >> > >> What: /sys/devices/.../removable > >> Date: May 2021 > >> Contact: Rajat Jain <rajatxjain@xxxxxxxxx> > >> Description: > >> Information about whether a given device can be removed from the > >> platform by the user. This is determined by its subsystem in a > >> bus / platform-specific way. This attribute is only present for > >> devices that can support determining such information: > >> > >> "removable": device can be removed from the platform by the user > >> "fixed": device is fixed to the platform / cannot be removed > >> by the user. > >> "unknown": The information is unavailable / cannot be deduced. > >> > >> Currently this is only supported by USB (which infers the > >> information from a combination of hub descriptor bits and > >> platform-specific data such as ACPI) and PCI (which gets this > >> from ACPI / device tree). > >> > >> It specifically talks about _platform_, not about properties of some > >> peripheral attached to a system. Note that the wording is very similar > >> to what we had for USB devices that originally implemented "removable" > >> attribute: > > In that case, shouldn't Rajat's patch change go into the driver core > > rather than the hub driver? _Every_ device downstream from a > > removable link should count as removable, yes? Not just the USB > > devices. > In theory yes. If your HC is removable by that logic every device is. > That renders the information content of 'removable' to zero. Everything > is removable. So we should add a new attribute. Call it "unpluggable", perhaps. It will say whether the device's immediate upstream link is hot-unpluggable. Then the device is removable if its parent is removable or if it is unpluggable. > > And to say that the attribute is supported only by USB and PCI is > > misleading, since it applies to every device downstream from a > > removable link. > Exactly and it is a difference. If you know that a device is removable > you must not disable hotplug detection on that port if you want full > functionality. While if you know that a device is not removable you may > straight up cut power, even if the _parent_ is still removable. > > The device tree is a tree and if you want to know whether hotplugging > is possible (let's ignore hibernation), you need to walk the tree top to > bottom. Adding the "unpluggable" attribute should take care of this, right? Alan Stern
