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    Subject[PATCH AUTOSEL 4.4 20/38] ALSA: usb-audio: Don't call usb_set_interface() at trigger callback
    Date
    From: Takashi Iwai <tiwai@suse.de>

    [ Upstream commit 4974b7950929e4a28d4eaee48e4ad07f168ac132 ]

    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: Keith Milner <kamilner@superlative.org>
    Tested-by: Dylan Robinson <dylan_robinson@motu.com>
    Link: https://lore.kernel.org/r/20201123085347.19667-3-tiwai@suse.de
    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    sound/usb/pcm.c | 28 +++++++++++++---------------
    1 file changed, 13 insertions(+), 15 deletions(-)

    diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
    index 366813f1a5f80..59f3a9492d74b 100644
    --- a/sound/usb/pcm.c
    +++ b/sound/usb/pcm.c
    @@ -242,21 +242,6 @@ static int start_endpoints(struct snd_usb_substream *subs)
    !test_and_set_bit(SUBSTREAM_FLAG_SYNC_EP_STARTED, &subs->flags)) {
    struct snd_usb_endpoint *ep = subs->sync_endpoint;

    - if (subs->data_endpoint->iface != subs->sync_endpoint->iface ||
    - subs->data_endpoint->altsetting != subs->sync_endpoint->altsetting) {
    - err = usb_set_interface(subs->dev,
    - subs->sync_endpoint->iface,
    - subs->sync_endpoint->altsetting);
    - if (err < 0) {
    - clear_bit(SUBSTREAM_FLAG_SYNC_EP_STARTED, &subs->flags);
    - dev_err(&subs->dev->dev,
    - "%d:%d: cannot set interface (%d)\n",
    - subs->sync_endpoint->iface,
    - subs->sync_endpoint->altsetting, err);
    - return -EIO;
    - }
    - }
    -
    dev_dbg(&subs->dev->dev, "Starting sync EP @%p\n", ep);

    ep->sync_slave = subs->data_endpoint;
    @@ -489,6 +474,19 @@ static int set_sync_endpoint(struct snd_usb_substream *subs,

    subs->data_endpoint->sync_master = subs->sync_endpoint;

    + if (subs->data_endpoint->iface != subs->sync_endpoint->iface ||
    + subs->data_endpoint->altsetting != subs->sync_endpoint->altsetting) {
    + err = usb_set_interface(subs->dev,
    + subs->sync_endpoint->iface,
    + subs->sync_endpoint->altsetting);
    + if (err < 0)
    + return err;
    + dev_dbg(&dev->dev, "setting usb interface %d:%d\n",
    + subs->sync_endpoint->iface,
    + subs->sync_endpoint->altsetting);
    + snd_usb_set_interface_quirk(dev);
    + }
    +
    return 0;
    }

    --
    2.27.0
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