Re: [BUG] ALSA: usb-audio: Scarlett 2 mixer driver fails on ehci-pci

["Geoffrey D. Bennett" <g@b4.vu>]

On Tue, May 18, 2021 at 06:41:45PM -0300, Geraldo Nascimento wrote:
[...]
> Myself I'd hook printk()'s to both ehci_hcd and xhci_hcd to print
> every possible variable involved and see if there's any relevant
> mismatches. Oh and watch with the printk()'s what libusb seems to be
> doing, too.
> 
> When you subscribe to linux-usb you *may* want to Cc: Greg
> Kroah-Hartman with your discoveries so far, he's the USB Subsystem
> Maintainer and the best one to help you track this down.

Thanks for the pointers!

It turns out that usb_sndctrlpipe() is not short for "USB sound
control pipe".

diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c
index 560c2ade829d..dcff3e3a49f3 100644
--- a/sound/usb/mixer_scarlett_gen2.c
+++ b/sound/usb/mixer_scarlett_gen2.c
@@ -635,7 +635,7 @@ static int scarlett2_usb(
 	/* send a second message to get the response */
 
 	err = snd_usb_ctl_msg(mixer->chip->dev,
-			usb_sndctrlpipe(mixer->chip->dev, 0),
+			usb_rcvctrlpipe(mixer->chip->dev, 0),
 			SCARLETT2_USB_VENDOR_SPECIFIC_CMD_RESP,
 			USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,
 			0,

I'll properly submit the patch once I've got confirmation from someone
else that this fixes the issue.

Thanks again,
Geoffrey.