Hi Takashi,
On 7/25/2023 2:27 AM, Takashi Iwai wrote:
On Tue, 25 Jul 2023 11:15:11 +0200,
Pierre-Louis Bossart wrote:
On 7/25/23 04:34, Wesley Cheng wrote:
In case of notifying SND platform drivers of connection events, some of
these use cases, such as offloading, require an ASoC USB backend device to
be initialized before the events can be handled. If the USB backend device
has not yet been probed, this leads to missing initial USB audio device
connection events.
Expose an API that traverses the usb_chip array for connected devices, and
to call the respective connection callback registered to the SND platform
driver.
Signed-off-by: Wesley Cheng <quic_wcheng@xxxxxxxxxxx>
---
sound/usb/card.c | 19 +++++++++++++++++++
sound/usb/card.h | 2 ++
2 files changed, 21 insertions(+)
diff --git a/sound/usb/card.c b/sound/usb/card.c
index 365f6d978608..27a89aaa0bf3 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -170,6 +170,25 @@ struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
}
EXPORT_SYMBOL_GPL(snd_usb_find_suppported_substream);
+/*
+ * in case the platform driver was not ready at the time of USB SND
+ * device connect, expose an API to discover all connected USB devices
+ * so it can populate any dependent resources/structures.
+ */
+void snd_usb_rediscover_devices(void)
+{
+ int i;
+
+ mutex_lock(®ister_mutex);
+ for (i = 0; i < SNDRV_CARDS; i++) {
+ if (usb_chip[i])
+ if (platform_ops && platform_ops->connect_cb)
+ platform_ops->connect_cb(usb_chip[i]);
what happens if the USB device is removed while the platform device adds
a port?
That should be protected by the register_mutex. But there can be
other races (see below :)
This sounds super-racy to me. It's the same set of problems we're having
between audio and display/DRM, I would be surprised if this function
dealt with all corner cases of insertion/removal, bind/unbind.
Yes, we need to be more careful about binding.
For example, in the current patch set, I see no way to prevent
unloading snd-usb-audio-qmi module, and it allows user to cut off the
stuff during operation, which may break things while the kernel is
running the code of the unloaded module. You need to have a proper
module refcount management for avoiding such a scenario. Most of
drivers don't need it because ALSA core part already takes care of
it. But in this case, it requires a manual adjustment.
Sorry for the delayed response...this was routed to another folder, and
missed it.
I see, that is a valid situation, so I think the best way to address it
is to do something like the following:
static void __exit qc_usb_audio_offload_exit(void)
{
...
snd_usb_unregister_platform_ops();
for (idx = 0; idx < SNDRV_CARDS; idx++)
qc_usb_audio_offload_disconnect(uadev[idx].chip);
We'll first unregister the platform ops, so that we get no further
connect/disconnect CBs, and then we'll forcefully ensure that all
devices are removed/cleaned. Part of the USB offload disconnect
sequence will also forcefully stop the offload path on the external DSP
by issuing a disconnect indication QMI message.
Then we can safely clean up the rest of the resources. We do have
refcounting in place for several of the other structures, but I think in
the module exit case, we need to ensure the offload path is stopped fully.
Thanks
Wesley Cheng
