[alsa-devel] [WIP PATCH] Scarlett mixer interface for 6i6, 18i6, 18i8 and 18i20.

[Tobias Hoffmann]

One more thing:

On 07/10/14 17:16, David Henningsson wrote:
> +	/* initialize sampling rate to 48000 */
> +	err = set_ctl_urb2(mixer->chip, UAC2_CS_CUR, 0x0100, 0x29, "\x80\xbb\x00\x00", 4);
> +	if (err<  0)
> +		return err;
> +

There have been two reports of users that had to replace the 
set_ctl_urb2 line with:

    char buffer[4] = { '\x80', '\xbb', '\x00', '\x00' };
    err = set_ctl_urb2(mixer->chip, UAC2_CS_CUR, 0x0100, 0x29, buffer, 4);

otherwise they would get a kernel oops, e.g.:

   BUG: unable to handle kernel paging request at ffffffffa0b43440
   IP: [<ffffffff8136f3c2>] memcpy+0x12/0x110
   ...
   Call Trace:
     [<ffffffffa0b311d2>] ? snd_usb_ctl_msg+0xc2/0x160 [snd_usb_audio]
     [<ffffffffa0b3b7aa>] set_ctl_urb2+0xaa/0x100 [snd_usb_audio]
     [<ffffffffa0b3c9fa>] scarlett_mixer_controls+0x28a/0x4c0 
[snd_usb_audio]
   ...

I'm not sure, why this happen, and why only for very few users.
Maybe it has to do with a particular compiler, or some kernel config 
setting that places the bytes "somewhere else" when they are passed as 
string?

   Tobias