At Sun, 09 Nov 2014 00:30:48 +1100, Damien Zammit wrote:
Hi Takashi,
On 07/11/14 01:12, Takashi Iwai wrote:
At Tue, 4 Nov 2014 11:06:36 +1100, Damien Zammit wrote:
down_read(&mixer->chip->shutdown_rwsem);I dont know what down_read and up_read does.
This is to protect against the disconnect and autopm. If you touch the USB hardware, do lock with this.
if (mixer->chip->shutdown) {err = -ENODEV;} else {err = snd_usb_ctl_msg(mixer->chip->dev,usb_rcvctrlpipe(mixer->chip->dev, 0), 0x81,USB_DIR_IN |USB_TYPE_CLASS |USB_RECIP_INTERFACE, 0x00, 0x500, buff, 1);if (err < 0)return err;err = snd_usb_ctl_msg(mixer->chip->dev,usb_rcvctrlpipe(mixer->chip->dev, 0), 0x81,USB_DIR_IN |USB_TYPE_CLASS |USB_RECIP_ENDPOINT, 0x100, 0x81, buff, 3);if (err < 0)return err;What do these two messages and why needed?
These two messages are the first half of the SPDIF mode selection. The device does not respond to standard mixer commands. I snooped the bus in Windows and replayed the packets when selecting SPDIF mode. Basically it appears that this command sets the mode of the device to receive the SPDIF clock source setting.
Then add the comment explaining that. There is absolutely no reason not to add any comment for such a black magic.
if (new_val == 0) {buff[0] = 0x80;buff[1] = 0xbb;buff[2] = 0x00;} else {buff[0] = buff[1] = buff[2] = 0;}If the mixer control is cleared to internal clock mode, the device expects the next command to have the sample rate fed in. Otherwise if the mixer control is set to spdif mode, the buffer is fed 3 zero bytes instead. It does not work as expected if the sample rate is allowed to be changed by the user, therefore I locked the sample rate to 48kHz.
Ditto. Give more comments.
err = snd_usb_ctl_msg(mixer->chip->dev,usb_sndctrlpipe(mixer->chip->dev, 0), 0x1,USB_TYPE_CLASS |USB_RECIP_ENDPOINT, 0x100, 0x81, buff, 3);if (err < 0)return err;err = snd_usb_ctl_msg(mixer->chip->dev,usb_rcvctrlpipe(mixer->chip->dev, 0), 0x81,USB_DIR_IN |USB_TYPE_CLASS |USB_RECIP_ENDPOINT, 0x100, 0x81, buff, 3);if (err < 0)return err;err = snd_usb_ctl_msg(mixer->chip->dev,usb_rcvctrlpipe(mixer->chip->dev, 0), 0x81,USB_DIR_IN |USB_TYPE_CLASS |USB_RECIP_ENDPOINT, 0x100, 0x2, buff, 3);if (err < 0)return err;This is where the magic happens...
And yet give more comments.
up_read(&mixer->chip->shutdown_rwsem);No idea what up_read is for.
Thanks for the review, and I will post a new patch soon. How do I tell git send-email to reply to this thread?
For the revised patch series, you shouldn't connect to the old thread. Hanging too deeply make often rather difficult to read.
Takashi