HI Hans,
On 30 June 2015 at 14:20, Hans de Goede hdegoede@redhat.com wrote:
Hi,
On 06/30/2015 06:07 PM, Simon Glass wrote:
<snip>
Instead, I wonder if we can remove the children when we probe the bus?
That should work, but I do not really see any advantage in that, removing the children is not that expensive and it feels like a kludge.
That's how it currently works, from what I can see in the code. But since there is a 'usb_started' boolean this is irrelevant.
Also, what happens to children that are in the device tree - i.e. static USB devices like WiFi? The device tree might have parameters for them. Still, that might not matter as I'm not sure that case is handled correctly today.
AFAIK there is no such thing as usb devices in devicetree, which makes sense as usb is a fully discoverable bus.
Sort-of. But as with PCI it is useful to be able to add settings for the devices in some cases. You can match them using vendor/device or interface IDs. Then the driver can access its settings.
AFAIK there is not a single example of having settings in devicetree for an usb device, since usb-devices are always 100% self describing since usb is a bus designed for hot(un)plug from the outset.
That's why I'm suggesting we unbind the devices that are no-longer present.
You're asking to make the code more complicated here using a what if reasoning with a "what if" which is likely to never happen.
> > The result of this commit is best seen in the output of "dm tree" > after > plugging out an usb hub with 2 devices plugges in and plugging in a > keyb. > instead, before this commit the output would be: > > usb [ + ] `-- sunxi-musb > usb_hub [ ] |-- usb_hub > usb_mass_st [ ] | |-- usb_mass_storage > usb_dev_gen [ ] | `-- generic_bus_0_dev_3 > usb_dev_gen [ + ] `-- generic_bus_0_dev_1 > > Notice the non active usb_hub child and its 2 non active children. > The > first child being non-active as in this example also causes > usb_get_dev_index > to return NULL when probing the first child, which results in the usb > kbd > code not binding to the keyboard.
Although I suspect that could be fixed.
Right, but just removing the children is a much cleaner solution, and also makes the output of "dm tree" properly reflect reality.
True, although you also have 'usb tree' for that. Another option would be to mark devices that were found and remove the others after the scan.
That seems like needless complexity. I believe that simply removing + unbinding the children on usb_stop is the right thing to do, and it also is the KISS solution.
I'm good with the remove(), but less sure about the unbind().
The unbind is necessary for usb_get_dev_index() to work properly, which is necessary for proper output of "usb tree" and for driver binding to work properly, without the unbind usb-keyboards will e.g. not work in certain circumstances.
The state of 'dm tree' does not bother me,
The state if dm tree is what usb_get_dev_index() works from, so if it is not in a good state, then usb_get_dev_index() will not work.
and I worry that we then limit our ability to use usb_find_child() to locate a device's parameters (i.e. support for more complex devices which need settings might be harder).
Again this is a what if reasoning for a hypothetical future problem which will likely never happen, where as the broken state of the dm tree after a "usb reset" is causing real problems.
For now, can we just leave this alone? I really don't want to re-visit this later.
Nope we cannot leave this alone, without unbinding usb devices which no longer exist, the dm tree will be broken and with it usb_get_dev_index() and through usb_get_dev_index() the keyboard driver.
We really should not be calling usb_get_dev_index() from the keyboard driver - that function is an interim port-helper. If it were ported fully to driver model it could use USB_DEVICE() like mass storage. We could fairly easily change the devnum to 0 for all devices instead of deleting them, and I suspect that would solve the problem.
But we would have to port usb ethernet which uses the same technique.
Anyway I think you've persuaded me that I might be worrying too much about what is to come. USB is not really the same as PCI in the sense that settings don't seem to be added to the device like PCI. Let's go with your approach. We still have the USB emulation stuff working, and that's the only real use case today.
Regards, Simon