Hi,
On 25-03-19 16:17, Hans de Goede wrote:
Hi,
On 25-03-19 16:12, Benjamin Tissoires wrote:
On Mon, Mar 25, 2019 at 11:57 AM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
Hi,
On 25-03-19 11:54, Benjamin Tissoires wrote:
On Thu, Mar 21, 2019 at 3:51 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
Recent kernels allow the generic-hid driver to be used as fallback for
devices with a specialized driver, when the hiddev is not listed in
hid_have_special_driver. Over time we are removing more and more
devices from the hid_have_special_driver table as devices get tested
to support this setup.
Before this commit the following happens when a HID device which has a
special-driver and is no longer listed in hid_have_special_driver, gets
enumerated:
1) device_add() gets called
2) bus_add_device() looks for a matching already registered hid driver,
and bind hid-generic to the new device
3) kobject_uevent(&dev->kobj, KOBJ_ADD) gets called notifying userspace of
the new hid_dev. udev calls modprobe based on the modalias in the uevent
4) The special driver gets loaded by modprobe
5) __hid_bus_reprobe_drivers() unbinds hid-generic and binds the new driver
There are a couple of downsides to this:
a) The probing messages printend when a HID driver bounds show up twice in
dmesg, which is confusing for the user
b) The (un)binding typically causes one or more evdev device-nodes to get
(un)registed firing of udev events to which e.g. the xserver responds by
(un)registering xinput devices and reporting this to interested clients.
IOW the i. bind generic, ii. unbind generic, iii. bind special driver dance
sets in motion a whole chain of events each step, while we really only want
the events from step iii. to be reported to userspace.
This commits introduces a request_module call before the device_add()
call, so that the special-driver is loaded when step 2) looks for a
matching driver and we directly bind the specialized driver.
Note the request_module call translates to an execve("/sbin/modprobe", ...)
and we now do this for each HID device added. So this is not entirely free,
but adding HID devices is not something which happens 100s of times a
second, so this should be fine.
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
---
This seems good, but I do wonder if there is a catch or not.
IIRC (I might be wrong), calling request_module() would try to load a
module synchronously. So what happens if you are in the initramfs
where you do not have any extra modules?
Would this result in a timeout and add a delay or will this
"immediately" return?
You are right that the /sbin/modprobe call is synchronously, that
is request_module will wait for the modprobe process to exit, note
it waits for modprobe to exit, not for the module to show up.
> I am just worried this will not add some delays during boot.
So AFAIK (and in my testing, I did specifically measure my systems
boot time before and after), this will not cause additional delays,
if the module is not present in the initrd, modprobe will simply fail
to load it and exit immediately.
OK, good.
However, when testing the commit with a Logitech Unifying, hid-generic
still loads prior to hid-logitech-dj. But when creating the DJ
devices, hid-logitech-hidpp is loaded and we do not see hid-generic
for those devices.
Any ideas what could explain this?
First hunch: the creation of hid_device-s from the usbhid driver does
not go through hid_add_device ? Just a hunch I did not check.
Ok, so that clearly is not the cause.
I can reproduce the problem and after 1.5 hours of debugging I've this
fixed now. The problem is we should not add a '\n' at the end of the
string we pass to request_module. I copied the code building the
string from modalias_show() where the \n does belong and did not
notice this :|
The reasons things were working with hid-logitech-dj.ko is because
it contains the following modalias: "hid:b0003g0102v0000046Dp*" where
the ending '*' happily matches the superfluous '\n' at the end.
I'll send a v2 fixing this.
Regards,
Hans
