Re: [PATCH] usb: gadget: f_midi: fix MIDI Streaming descriptor lengths

[Takashi Iwai <tiwai@suse.de>]

On Wed, 29 Jan 2025 18:31:35 +0100,
John Keeping wrote:
> 
> 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.
> 
> From the same config, the jack definitions are:
> 
> 	1:  IN  External
> 	2:  OUT Embedded, source 1
> 	3:  IN  External
> 	4:  OUT Embedded, source 3
> 	5:  IN  External
> 	6:  OUT Embedded, source 5
> 	7:  IN  External
> 	8:  OUT Embedded, source 7
> 
> 	9:  IN  Embedded
> 	10: OUT External, source 9
> 	11: IN  Embedded
> 	12: OUT External, source 11
> 
> So it seems that the first 2 entries in each endpoint list are correct.
> For the OUT endpoint, jacks 9 and 11 are embedded IN jacks and for the
> IN endpoint, jacks 2 and 4 are embedded OUT jacks.
> 
> The problem is that the OUT endpoint lists two extra invalid jack IDs
> and the IN endpoint should list jacks 6 and 8 but does not.
> 
> After applying this patch, the endpoint descriptors for the same config
> are:
> 
>       Endpoint Descriptor:
>         [...]
>         bEndpointAddress     0x01  EP 1 OUT
>         [...]
>         MIDIStreaming Endpoint Descriptor:
>           bLength                 6
>           bDescriptorType        37
>           bDescriptorSubtype      1 (Invalid)
>           bNumEmbMIDIJack         2
>           baAssocJackID( 0)       9
>           baAssocJackID( 1)      11
>       Endpoint Descriptor:
>         [...]
>         bEndpointAddress     0x81  EP 1 IN
>         [...]
>         MIDIStreaming Endpoint Descriptor:
>           bLength                 8
>           bDescriptorType        37
>           bDescriptorSubtype      1 (Invalid)
>           bNumEmbMIDIJack         4
>           baAssocJackID( 0)       2
>           baAssocJackID( 1)       4
>           baAssocJackID( 2)       6
>           baAssocJackID( 3)       8
> 
> Which lists all the jack IDs where they should be.

Hmm, I don't get your point.  The embedded IN is paired with the
external OUT.  That's the intended behavior, no?


Takashi

> 
> 
> Regards,
> John
> 
> > > Cc: stable@vger.kernel.org
> > > Fixes: c8933c3f79568 ("USB: gadget: f_midi: allow a dynamic number of input and output ports")
> > > Signed-off-by: John Keeping <jkeeping@inmusicbrands.com>
> > > ---
> > >  drivers/usb/gadget/function/f_midi.c | 8 ++++----
> > >  1 file changed, 4 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
> > > index 837fcdfa3840f..6cc3d86cb4774 100644
> > > --- a/drivers/usb/gadget/function/f_midi.c
> > > +++ b/drivers/usb/gadget/function/f_midi.c
> > > @@ -1000,11 +1000,11 @@ static int f_midi_bind(struct usb_configuration *c, struct usb_function *f)
> > >  	}
> > >  
> > >  	/* configure the endpoint descriptors ... */
> > > -	ms_out_desc.bLength = USB_DT_MS_ENDPOINT_SIZE(midi->in_ports);
> > > -	ms_out_desc.bNumEmbMIDIJack = midi->in_ports;
> > > +	ms_out_desc.bLength = USB_DT_MS_ENDPOINT_SIZE(midi->out_ports);
> > > +	ms_out_desc.bNumEmbMIDIJack = midi->out_ports;
> > >  
> > > -	ms_in_desc.bLength = USB_DT_MS_ENDPOINT_SIZE(midi->out_ports);
> > > -	ms_in_desc.bNumEmbMIDIJack = midi->out_ports;
> > > +	ms_in_desc.bLength = USB_DT_MS_ENDPOINT_SIZE(midi->in_ports);
> > > +	ms_in_desc.bNumEmbMIDIJack = midi->in_ports;
> > >  
> > >  	/* ... and add them to the list */
> > >  	endpoint_descriptor_index = i;
> > > -- 
> > > 2.48.1
> > > 
> > >