On Wednesday 23 Aug 2017 14:52:43 Clemens Ladisch wrote:
> Keith A. Milner wrote:
> >>> kernel: [ 1987.452947] usb 1-1: Unable to change format on ep #8e:
> >>> already in use>
> > So the error messages are due to a userspace app trying to open playback
> > and capture at the same time?
>
> For this device, playback requires a running capture stream to determine
> the rate of packets. This error happens when the application tries to
> open the capture stream after the playback stream. (If the format does
> not actually need to change, the error message is misleading.)
>
> Your actual problem is that the device does not send any capture packets.
OK, I found some more time to look at this.
The background is a Roland device. The device descriptor is attached, but it
seems to be common to a lot of Roland devices.
Specifically on this device, the Playback endpoint is 0x0d and there is a
related Implicit feedback endpoint at 0x8e.
I have USB traces of the device operation under Windows and the (non)
operation under Linux. The primary difference seems to be that, under Windows,
the Implict Feedback endpoint (0x8e) is opened prior to playback commencing.
Given previous discussions (and further research) on Implicit feedback, this
makes sense.
Under Linux, this does not happen.
I've been studying the code in pcm.c and endpoint.c to work out why this is,
and have some questions on the code function.
The flow of the code to deal with implict feedback setup in pcm.c is, roughly,
as follows:
set_sync_endpoint
set_sync_ep_implicit_fb_quirk
search_roland_implicit_fb
set_sync_ep_implicit_fb_quirk seems to deal with quirks relating to implicit
feedback and, within this, is a specific check for Roland which ends up
branching to "add_sync_ep" which adds a new endpoint via endpoint.c function
snd_usb_add_endpoint and assigns this as as the sync endpoint:
subs->sync_endpoint = snd_usb_add_endpoint(subs->stream->chip,
alts, ep, !subs->direction,
SND_USB_ENDPOINT_TYPE_DATA);
subs->data_endpoint->sync_master = subs->sync_endpoint;
Within endpoint.c, this new endpoint is added to chip->ep_list :
list_add_tail(&ep->list, &chip->ep_list);
After set_sync_ep_implicit_fb_quirk has completed it returns to
set_sync_endpoint which then checks that there are at least 2 endpoints:
if (altsd->bNumEndpoints < 2)
return 0;
However, in the case I'm testing, on this device, this test fails as
bNumEndpoints is 1, even though we've just added a second endpoint for the
Implicit feedback.
Looking at the code, endpoint.c does not alter bNumEndpoints, which seems to
be a fundamental piece of data held against the usb_host_interface instance
and, presumably, set from the device descriptor by underlying kernel code.
My question is, is the test for bNumEndpoints correct here? From what I can
gather, the whole point of the set_sync_ep_implicit_fb_quirk and
search_roland_implicit_fb code is to add an endpoint that can then be used by
set_sync_endpoint, but this seems to be ignored by doing the test for
bNumEndpoints.
Or, perhaps, is it that the way that this endpoint is added is incorrect.
I have, by the way, tried commenting out the bNumEndpoints test, and it fails
at the subsequent sync-pipe check with:
invalid sync pipe. bmAttributes 00, bLength 0, bSynchAddress 00
To me this suggests the endpoint isn't being set correctly somehow.
Any pointers gratefully received.
Cheers,
Keith
Bus 001 Device 013: ID 0582:01d6 Roland Corp.
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.00
bDeviceClass 255 Vendor Specific Class
bDeviceSubClass 0
bDeviceProtocol 255
bMaxPacketSize0 64
idVendor 0x0582 Roland Corp.
idProduct 0x01d6
bcdDevice 0.00
iManufacturer 1 BOSS
iProduct 2 GT-1
iSerial 0
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 188
bNumInterfaces 4
bConfigurationValue 1
iConfiguration 0
bmAttributes 0xc0
Self Powered
MaxPower 0mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 255 Vendor Specific Class
bInterfaceSubClass 255 Vendor Specific Subclass
bInterfaceProtocol 0
iInterface 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 255 Vendor Specific Class
bInterfaceSubClass 2
bInterfaceProtocol 2
iInterface 0
** UNRECOGNIZED: 06 24 f1 01 00 00
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 1
bNumEndpoints 1
bInterfaceClass 255 Vendor Specific Class
bInterfaceSubClass 2
bInterfaceProtocol 2
iInterface 0
** UNRECOGNIZED: 07 24 01 01 00 01 00
** UNRECOGNIZED: 0b 24 02 01 02 04 18 01 44 ac 00
** UNRECOGNIZED: 06 24 f1 04 16 00
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x0d EP 13 OUT
bmAttributes 5
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Data
wMaxPacketSize 0x0038 1x 56 bytes
bInterval 1
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 2
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 255 Vendor Specific Class
bInterfaceSubClass 2
bInterfaceProtocol 1
iInterface 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 2
bAlternateSetting 1
bNumEndpoints 1
bInterfaceClass 255 Vendor Specific Class
bInterfaceSubClass 2
bInterfaceProtocol 1
iInterface 0
** UNRECOGNIZED: 07 24 01 07 00 01 00
** UNRECOGNIZED: 0b 24 02 01 02 04 18 01 44 ac 00
** UNRECOGNIZED: 06 24 f1 04 16 00
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x8e EP 14 IN
bmAttributes 37
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Implicit feedback Data
wMaxPacketSize 0x0038 1x 56 bytes
bInterval 1
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 3
bAlternateSetting 0
bNumEndpoints 2
bInterfaceClass 255 Vendor Specific Class
bInterfaceSubClass 3
bInterfaceProtocol 0
iInterface 0
** UNRECOGNIZED: 06 24 f1 02 01 01
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x03 EP 3 OUT
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0200 1x 512 bytes
bInterval 1
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x84 EP 4 IN
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0200 1x 512 bytes
bInterval 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 3
bAlternateSetting 1
bNumEndpoints 2
bInterfaceClass 255 Vendor Specific Class
bInterfaceSubClass 3
bInterfaceProtocol 0
iInterface 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x03 EP 3 OUT
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0200 1x 512 bytes
bInterval 4
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x85 EP 5 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0200 1x 512 bytes
bInterval 4
Device Qualifier (for other device speed):
bLength 10
bDescriptorType 6
bcdUSB 2.00
bDeviceClass 255 Vendor Specific Class
bDeviceSubClass 0
bDeviceProtocol 255
bMaxPacketSize0 64
bNumConfigurations 1
Device Status: 0x0001
Self Powered
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