On Wed, Jan 29, 2025 at 05:40:04PM +0100, Takashi Iwai wrote:
> On Wed, 29 Jan 2025 17:05:19 +0100,
> John Keeping wrote:
> >
> > In the two loops before setting the MIDIStreaming descriptors,
> > ms_in_desc.baAssocJackID[] has entries written for "in_ports" values and
> > ms_out_desc.baAssocJackID[] has entries written for "out_ports" values.
> > But the counts and lengths are set the other way round in the
> > descriptors.
> >
> > Fix the descriptors so that the bNumEmbMIDIJack values and the
> > descriptor lengths match the number of entries populated in the trailing
> > arrays.
>
> Are you sure that it's a correct change?
>
> IIUC, the in_ports and out_ports parameters are for external IN and
> OUT jacks, where an external OUT jack is connected to an embedded IN
> jack, and an external IN jack is connected to an embedded OUT jack.
I think it depends how the in_ports and out_ports values in configfs are
interpreted. However, the case where in_ports != out_ports has been
broken since these files were added!
Without this change, setting in_ports=4 out_ports=2 we end up with:
Endpoint Descriptor:
[...]
bEndpointAddress 0x01 EP 1 OUT
[...]
MIDIStreaming Endpoint Descriptor:
bLength 8
bDescriptorType 37
bDescriptorSubtype 1 (Invalid)
bNumEmbMIDIJack 4
baAssocJackID( 0) 9
baAssocJackID( 1) 11
baAssocJackID( 2) 9
baAssocJackID( 3) 0
Endpoint Descriptor:
[...]
bEndpointAddress 0x81 EP 1 IN
[...]
MIDIStreaming Endpoint Descriptor:
bLength 6
bDescriptorType 37
bDescriptorSubtype 1 (Invalid)
bNumEmbMIDIJack 2
baAssocJackID( 0) 2
baAssocJackID( 1) 4
Note that baAssocJackID values 2 and 3 on the OUT endpoint are wrong.
