A new module option, implicit_fb, is added to specify the driver
looking for the implicit feedback sync.  This can be useful for a
device that could be working better in the implicit feed back mode and
user wants to test it quickly.  When this works, we can add the quirk
entry easily.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-40-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

This patch extends the implicit feedback mode parser code to check the
description more generically, so that the quirk entries can be added
without the explicit EP and interface numbers.  The search is done for
the next and the previous interface of the given altset, and if both
entries are ASYNC mode and the direction matches, it just takes as the
sync endpoint.  The generic parser is applicable only for the playback
stream.

As of now, only a few M-Audio devices have been converted to use this
mode.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-39-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The code dealing with the implicit feedback mode grew recently, and
it's becoming messy.  As we receive more and more devices that need
the similar handling, it's better to be processed through a table
instead of the open code.

This patch moves the code that is relevant with parsing the implicit
feedback mode and some helpers into another file, implicit.c.  The
detection and the setup of the implicit feedback sync EPs are
rewritten to use the ID/class matching table instead.

There should be no functional changes.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-38-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The capture stream of BOSS GT-001 seems always requiring to be tied
with the playback stream.  OTOH, the playback stream of this device
doesn't seem working in the implicit fb mode, per se, since the
playback must be running before the capture stream.

This patch tries to address the points above:
- Avoid the implicit fb mode for the playback
- Set up a fake sync EP for the capture stream with the hard-coded
  playback stream using the implicit fb mode
Reported-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-37-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

Now the sync endpoints have been parsed at the beginning and won't be
changed dynamically, let's show them in the proc outputs for helping
debugging.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-36-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

Just for consistency, use unsigned char for iface and altsetting in
allover places.  Also rearrange the field positions of
snd_usb_endpiont and tidy up with some comments.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-35-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

Follow the inclusive terminology, just replace sync_master/sync_slave
with sync_source/sync_sink.  It's also a bit clearer from its meaning,
too.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-34-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

There are multiple places in format.c performing the similar code for
setting the rate_min, rate_max and rates fields.  This patch unifies
those in a helper function and calls it at the end of the parser phase
so that all rate_table entries have been already determined.

No functional changes, just a minor code refactoring.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-33-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

There are two places calculating the next packet size for the playback
stream in the exactly same way.  Provide the single helper for this
purpose and use it from both places gracefully.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-32-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

Some fields like interface and alt_idx in snd_usb_substream are mostly
useless now as they can be referred via either cur_audiofmt or
data_endpoint assigned to the substream.  Drop those, and also assure
the concurrency about the access of cur_audiofmt field.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-31-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

Minor code refactoring to consolidate the URB deactivation code in
endpoint.c.  A slight behavior change is that the error handling in
snd_usb_endpoint_start() leaves EP_FLAG_STOPPING now.  This should be
synced with the later PCM sync_stop callback.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-30-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The endpoint objects may be started/stopped concurrently by different
substreams in the case of implicit feedback mode, while the current
code handles the reference counter without any protection.

This patch changes the refcount to atomic_t for avoiding the
inconsistency.  We need no reference_t here as the refcount goes only
up to 2.

Also the name "use_count" is renamed to "running" since this is about
actually the running status, not the open refcount.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-29-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The audioformat is referred in many places but most of usages are
read-only.  Let's add const prefix in the possible places.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-28-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The implicit feedback mode uses a ring buffer for storing the received
packet sizes from the feedback source, and the code has a slight flaw;
when a playback stream stalls by some reason and the URBs aren't
processed, the next_packet FIFO might become empty, but the driver
can't distinguish whether it's empty or full because it's managed with
read_poss and write_pos.

This patch addresses those by changing the next_packet array
management.  Instead of keeping read and write positions, now the head
position and the queued amount are kept.  It's easier to understand
about the emptiness.  Also, the URB active flag is now cleared before
calling queue_pending_output_urbs() for avoiding (theoretically)
possible inconsistency.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-27-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

This is an intensive surgery for the endpoint and stream management
for achieving more robust and clean code.

The goals of this patch are:
- More clear endpoint resource changes
- The interface altsetting control in a single place
Below are brief description of the whole changes.

First off, most of the endpoint operations are moved into endpoint.c,
so that the snd_usb_endpoint object is only referred in other places.
The endpoint object is acquired and released via the new functions
snd_usb_endpoint_open() and snd_usb_endpoint_close() that are called
at PCM hw_params and hw_free callbacks, respectively.  Those are
ref-counted and EPs can manage the multiple opens.

The open callback receives the audioformat and hw_params arguments,
and those are used for initializing the EP parameters; especially the
endpoint, interface and altset numbers are read from there, as well as
the PCM parameters like the format, rate and channels.  Those are
stored in snd_usb_endpoint object.  If it's the secondary open, the
function checks whether the given parameters are compatible with the
already opened EP setup, too.

The coupling with a sync EP (including an implicit feedback sync) is
done by the sole snd_usb_endpoint_set_sync() call.

The configuration of each endpoint is done in a single shot via
snd_usb_endpoint_configure() call.  This is the place where most of
PCM configurations are done.  A few flags and special handling in the
snd_usb_substream are dropped along with this change.

A significant difference wrt the configuration from the previous code
is the order of USB host interface setups.  Now the interface is
always disabled at beginning and (re-)enabled at the last step of
snd_usb_endpoint_configure(), in order to be compliant with the
standard UAC2/3.  For UAC1, the interface is set before the parameter
setups since there seem devices that require it (e.g. Yamaha THR10),
just like how it was done in the previous driver code.

The start/stop are almost same as before, also single-shots.  The URB
callbacks need to be set via snd_usb_endpoint_set_callback() like the
previous code at the trigger phase, too.

Finally, the flag for the re-setup is set at the device suspend
through the full EP list, instead of PCM trigger.  This catches the
overlooked cases where the PCM hasn't been running yet but the device
needs the full setup after resume.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-26-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The function to evaluate the match of the parameters with an EP
assumes only the discrete rate tables and doesn't handle the
continuous rates properly.

This patch fixes match_endpoint_audioformats() to handle the
continuous rates.  Also the almost useless debug prints there are
dropped.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-25-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The commit 92adc96f ("ALSA: usb-audio: set the interface format
after resume on Dell WD19") introduced the workaround for the broken
setup after the resume specifically on a Dell dock model.  However,
the full setup should have been performed after the resume on all
devices, as we can't guarantee the same state.  So this patch removes
the conditional check and applies the workaround always.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-24-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The prepare_data_urb and retire_data_urb fields of the endpoint object
are set dynamically at PCM trigger start/stop.  Those are evaluated in
the endpoint handler, but there can be a race, especially if two
different PCM substreams are handling the same endpoint for the
implicit feedback case.  Also, the data_subs field of the endpoint is
set and accessed dynamically, too, which has the same risk.

As a slight improvement for the concurrency, this patch introduces the
function to set the callbacks and the data in a shot with the memory
barrier.  In the reader side, it's also fetched with the memory
barrier.

There is still a room of race if prepare and retire callbacks are set
during executing the URB completion.  But such an inconsistency may
happen only for the implicit fb source, i.e. it's only about the
capture stream.  And luckily, the capture stream never sets the
prepare callback, hence the problem doesn't happen practically.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-23-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

start_endpoints() may leave the data endpoint running if an error
happens at starting the sync endpoint.  We should stop both streams
properly, instead.

While we're at it, move the debug prints into the endpoint.c that is a
more suitable place.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-22-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

A preliminary change for the later big changes.  This is a minor code
refactoring to drop the unnecessary arguments that can be retrieved in
a different way.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-21-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

A preliminary change for the later big changes.  This is a minor code
refactoring to drop the unnecessary arguments that can be retrieved in
a different way.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-20-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

A preliminary patch for the later big change.  Just a minor code
refactoring.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-19-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

Setting the active altsetting at changing sample rate seems
unrecommended.  The host should deselect the altsetting at first
before that, then select it again.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-18-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

Add a helper function to retrieve the usb_host_interface object from
the given interface and altsetting number pair, which is a commonly
used procedure in the driver code.

No functional changes, just minor code refactoring.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-17-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

This behavior turned out to be invalid from the USB spec POV and
shouldn't be applied.  As it's an optional flag that is set only via
an card control element that must be hardly used, let's drop it
again.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-16-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

Currently snd_usb_endpoint objects are created at first when the
substream is opened and tries to assign the endpoints corresponding to
the matching audioformat.  But since basically the all endpoints have
been already parsed and the information have been obtained, we may
create the endpoint objects statically at the init phase.  It's easier
to manage for the implicit fb case, for example.

This patch changes the endpoint object management and lets the parser
to create the all endpoint objects.

This change shouldn't bring any functional changes.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-15-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The implicit feedback mode initializes both the main data stream and
the sync data stream.  When a sync stream was already opened, this
would result in the doubly initialization and might screw up things.

Add the check of already opened sync streams and skip the unnecessary
initialization.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-14-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The file debug.h contains a simple macro for debug prints, and it's
used only in two places, the format parser and the hw_params rules.
The former actually should print a more informative message instead,
so the only users are the hw_parmas rules.

This patch moves the contents of debug.h into the hw_params rules
local code and remove the unneeded includes.  Also, the debug print in
the format parser is replaced with the information print with more
useful information, and the raw printk() call is replaced with
pr_debug().
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-13-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

Several hw_params functions narrows the interval via min/max rule in
the very similar way, so factor out those into a helper function and
use commonly.

No functional changes, just minor code refactoring.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-12-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

In the current code, there is no check at the stream open time whether
the endpoint is being already used by others.  In the normal
operations, this shouldn't happen, but in the case of the implicit
feedback mode, it's a common problem with the full duplex operation,
because the capture stream is always opened by the playback stream as
an implicit sync source.

Although we recently introduced the check of such a conflict of
parameters at the PCM hw_params time, it doesn't give any hint at the
hw_params itself and just gives the error.  This isn't quite
comfortable, and it caused problems on many applications.

This patch attempts to make the parameter handling easier by
introducing the strict hw constraint matching with the counterpart
stream that is being used.  That said, when an implicit feedback
playback stream is running before a capture stream is opened, the
capture stream carries the PCM hw-constraint to allow only the same
sample rate, format, periods and period frames as the running playback
stream.  If not opened or there is no conflict of endpoints, the
behavior remains as same as before.

Note that this kind of "weak link" should work for most cases, but
this is no concrete solution; e.g. if an application changes the hw
params multiple times while another stream is opened, this would lead
to inconsistencies.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-11-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

This is a preliminary work for the upcoming hw-constraint change for
the implicit feedback mode.

Currently snd_usb_autoresume() is called at the end of
setup_hwinfo().  It's a bit confusing; because of this implicit
refcount usage, the caller side needs to call snd_usb_autosuspend()
later in the error path although it's not seen inside the function.
Instead, it's clearer to call both snd_usb_autoresume() and suspend()
in the very same function.

It's only refactoring and no functional changes.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-10-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

Instead of parsing and evaluating the sync endpoint and the implicit
feedback mode at each time the audio stream is opened, let's parse it
once at the probe time, as the all needed information can be obtained
statically from the descriptor or from the quirk.

This patch extends audioformat struct to record the sync endpoint,
interface and altsetting as well as the implicit feedback flag, which
are filled at parsing the streams.  Then, set_sync_endpoint() is much
simplified just to follow the already parsed data.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-9-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

There are a few rooms for improvements wrt the debug prints:
- The EP debug print is shown only at starting, not at stopping
- The EP debug print contains useless object addresses
- Some helpers show the urb and the EP object addresses, too

This patch addresses those shortcomings.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-8-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The sync EP setup isn't cleared at stopping the stream but expected to
be cleared at the next stream start.  This may leave the sync link
setup stale and can spoof wrongly when full duplex streams were
running in the implicit fb sync.  Let's initialize them properly at
start and end of the stream.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-7-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

Factor out the code to obtain snd_usb_endpoint object matching with
the given endpoint.  It'll be used in the later patch to add the
implicit feedback hw-constraint.

No functional change by this patch itself.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-6-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

It seems that many UAC2 devices are with the implicit feedback, but
they couldn't be probed properly because the assumption the driver
takes currently isn't applied: they have the single endpoint for both
data and implicit-fb streams, while we checked only the classical sync
endpoints assigned to the next altsetting in the same interface.

This patch extends the search to match with those typical cases where
the implicit fb stream is found in the next interface number.

While we're at it, slightly refactor the code, not returning 0/-ERROR
but use the standard bool to success/failur, which is more intuitive
in this particular case.
Reported-by: NDylan Robinson <dylan_robinson@motu.com>
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-5-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The current driver code assumes blindly that all found sample rates for
the same endpoint from the UAC2 and UAC3 descriptors can be used no
matter which altsetting, but actually this was wrong: some devices
accept only limited sample rates in each altsetting.  For determining
which altsetting supports which rate, we need to verify each sample rate
and check the validity via UAC2_AS_VAL_ALT_SETTINGS.  This control
reports back the available altsettings as a bitmap.

This patch implements the missing piece above, the verification and
reconstructs the sample rate tables based on the result.

An open question is how to deal with the altsettings that ended up
with no valid sample rates after verification.  At least, there is a
device that showed this problem although the sample rates did work in
the later usage (see bug link).  For now, we accept such an altset as
is, assuming that it's a firmware bug.
Reported-by: NDylan Robinson <dylan_robinson@motu.com>
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
BugLink: https://bugzilla.suse.com/show_bug.cgi?id=1178203
Link: https://lore.kernel.org/r/20201123085347.19667-4-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

The PCM trigger callback is atomic, hence we must not call a function
like usb_set_interface() there.  Calling it from there would lead to a
kernel Oops.

Fix it by moving the usb_set_interface() call to set_sync_endpoint().

Also, apply the snd_usb_set_interface_quirk() for consistency, too.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-3-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

In the current code, when the device provides the discrete sample rate
tables with unusual sample rates, the driver tries to gather the whole
values from the audioformat entries and create a hw-constraint rule to
restrict with this single rate list.  This is rather inefficient and
may overlook the rates that are associated only with the certain
audioformat entries.

This patch improves the hw constraint setup by rewriting the existing
hw_rule_rate().  The discrete sample rates (identified by rate_table
and nr_rates of format entry) are checked in the existing
hw_rule_rate() instead of extra rules; in the case of discrete rates,
the function compares with each rate table entry and calculates the
min/max values from there.  For the contiguous rates, the behavior
doesn't change.

Along with it, snd_usb_pcm_check_knot() and snb_usb_substream
rate_list field become superfluous, thus those are dropped.
Tested-by: NKeith Milner <kamilner@superlative.org>
Tested-by: NDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-2-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

Found one more Logitech device, BCC950 ConferenceCam, which needs
the same delay here. This makes 3 out of 3 devices I have tried.

Therefore, add a delay for all Logitech devices as it does not hurt.
Signed-off-by: NJoakim Tjernlund <joakim.tjernlund@infinera.com>
Cc: <stable@vger.kernel.org> # 4.19.y, 5.4.y
Link: https://lore.kernel.org/r/20201117122803.24310-1-joakim.tjernlund@infinera.comSigned-off-by: NTakashi Iwai <tiwai@suse.de>