diff options
| author | Ruslan Bilovol <ruslan.bilovol@gmail.com> | 2021-06-04 00:01:04 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-06-09 11:26:49 +0200 |
| commit | e89bb4288378b85c82212b60dc98ecda6b3d3a70 (patch) | |
| tree | 902329a9974240b3a8fe129d0e890e2dcd680cf1 /drivers/usb/gadget/function/u_audio.h | |
| parent | 40c73b30546e759bedcec607fedc2d4be954508f (diff) | |
usb: gadget: u_audio: add real feedback implementation
This adds interface between userspace and feedback endpoint to report real
feedback frequency to the Host.
Current implementation adds new userspace interface ALSA mixer control
"Capture Pitch 1000000" (similar to aloop driver's "PCM Rate Shift 100000"
mixer control)
Value in PPM is chosen to have correction value agnostic of the actual HW
rate, which the application is not necessarily dealing with, while still
retaining a good enough precision to allow smooth clock correction on the
playback side, if necessary.
Similar to sound/usb/endpoint.c, a slow down is allowed up to 25%. This
has no impact on the required bandwidth. Speedup correction has an impact
on the bandwidth reserved for the isochronous endpoint. The default
allowed speedup is 500ppm. This seems to be more than enough but, if
necessary, this is configurable through a module parameter. The reserved
bandwidth is rounded up to the next packet size.
Usage of this new control is easy to implement in existing userspace tools
like alsaloop from alsa-utils.
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20210603220104.1216001-4-jbrunet@baylibre.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/usb/gadget/function/u_audio.h')
| -rw-r--r-- | drivers/usb/gadget/function/u_audio.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/drivers/usb/gadget/function/u_audio.h b/drivers/usb/gadget/function/u_audio.h index 53e6baf55cbf..a218cdf771fe 100644 --- a/drivers/usb/gadget/function/u_audio.h +++ b/drivers/usb/gadget/function/u_audio.h @@ -11,6 +11,14 @@ #include <linux/usb/composite.h> +/* + * Same maximum frequency deviation on the slower side as in + * sound/usb/endpoint.c. Value is expressed in per-mil deviation. + * The maximum deviation on the faster side will be provided as + * parameter, as it impacts the endpoint required bandwidth. + */ +#define FBACK_SLOW_MAX 250 + struct uac_params { /* playback */ int p_chmask; /* channel mask */ @@ -23,6 +31,7 @@ struct uac_params { int c_ssize; /* sample size */ int req_number; /* number of preallocated requests */ + int fb_max; /* upper frequency drift feedback limit per-mil */ }; struct g_audio { |