Re: [PATCH] USB: Add quirk for WORLDE easykey.25 MIDI keyboard

[Lukáš Lalinský]

On Tue, Jan 24, 2017 at 8:37 AM, Lukáš Lalinský <lu...@oxygene.sk> wrote:
> On Tue, Jan 24, 2017 at 8:32 AM, Oliver Neukum <oneu...@suse.com> wrote:
>> Am Montag, den 23.01.2017, 19:36 +0100 schrieb Lukáš Lalinský:
>>> I have uploaded both captures here -
>>> https://gist.github.com/lalinsky/83148a827d5cd43e79e377d8e1b5ed0d
>>
>> Indeed it is does not set a configuration. Either the capture
>> is incomplete or device and host violate the standard. A device
>> may be left unconfigured.
>
> Is this may or may not? I'm not familiar with USB, so I assumed if
> there is only one configuration and there is always one active, it
> does not need to be set explicitly because the correct one is already
> active.
>
>> We need to read the descriptors even if we
>> see only one configuration to get the power budgeting right.
>
> Aren't those in the CONFIGURATION descriptors? Reading the STRING
> descriptor is probably only useful if you need to print the
> configuration details somewhere.

I re-ran the capture on a Windows 7 host. The previous capture was
missing data, probably due to interactions of the Linux host and
Windows VM.

https://gist.github.com/lalinsky/2ec7d74b049b448b1f7032d8861ca4a2

It does set the configuration, but does not request the string descriptor.

Lukas
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Re: [PATCH] USB: Add quirk for WORLDE easykey.25 MIDI keyboard

[Lukáš Lalinský]

On Tue, Jan 24, 2017 at 8:32 AM, Oliver Neukum <oneu...@suse.com> wrote:
> Am Montag, den 23.01.2017, 19:36 +0100 schrieb Lukáš Lalinský:
>> I have uploaded both captures here -
>> https://gist.github.com/lalinsky/83148a827d5cd43e79e377d8e1b5ed0d
>
> Indeed it is does not set a configuration. Either the capture
> is incomplete or device and host violate the standard. A device
> may be left unconfigured.

Is this may or may not? I'm not familiar with USB, so I assumed if
there is only one configuration and there is always one active, it
does not need to be set explicitly because the correct one is already
active.

> We need to read the descriptors even if we
> see only one configuration to get the power budgeting right.

Aren't those in the CONFIGURATION descriptors? Reading the STRING
descriptor is probably only useful if you need to print the
configuration details somewhere.

> Does the device work without any .ini file?

Yes. It's a standard MIDI device, no configuration is required.

Lukas
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Re: [PATCH] USB: Add quirk for WORLDE easykey.25 MIDI keyboard

[Lukáš Lalinský]

On Sat, Jan 21, 2017 at 10:08 AM, Greg Kroah-Hartman
 wrote:
> Always use scripts/get_maintainer.pl to determine who to send patches
> to, and what mailing list.  You forgot linux-usb@vger, which I've now
> added...

I'm sorry about that. I actually did use scripts/get_maintainer.pl,
but it only returned your email address and I added linux-kernel@vger
myself. I guess I ran it with wrong options.

> That's odd, how does other operating systems handle this device?

I'm not sure how realistic this test is, but I ran a Wireshark capture
from Windows 8.1 VM and it seems that for this particular device,
Windows doesn't try to set the current configuration (since there is
only one) and it does not even attempt to get the configuration string
descriptor. I'm not sure if Windows does this in general, but it seems
to work around the problem for this device by not caring about the
configuration string descriptor in the first place.

I have uploaded both captures here -
https://gist.github.com/lalinsky/83148a827d5cd43e79e377d8e1b5ed0d

Lukas
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