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  • Takashi Iwai's avatar
    ALSA: usb-audio: Fix inconsistent card PM state after resume · 862b2509
    Takashi Iwai authored
    When a USB-audio interface gets runtime-suspended via auto-pm feature,
    the driver suspends all functionality and increment
    chip->num_suspended_intf.  Later on, when the system gets suspended to
    S3, the driver increments chip->num_suspended_intf again, skips the
    device changes, and sets the card power state to
    SNDRV_CTL_POWER_D3hot.  In return, when the system gets resumed from
    S3, the resume callback decrements chip->num_suspended_intf.  Since
    this refcount is still not zero (it's been runtime-suspended), the
    whole resume is skipped.  But there is a small pitfall here.
    
    The problem is that the driver doesn't restore the card power state
    after this resume call, leaving it as SNDRV_CTL_POWER_D3hot.  So,
    even after the system resume finishes, the card instance still appears
    as if it were system-suspended, and this confuses many ioctl accesses
    that are blocked unexpectedly.
    
    In details, we have two issues behind the scene: one is that the card
    power state is changed only when the refcount becomes zero, and
    another is that the prior auto-suspend check is kept in a boolean
    flag.  Although the latter problem is almost negligible since the
    auto-pm feature is imposed only on the primary interface, but this can
    be a potential problem on the devices with multiple interfaces.
    
    This patch addresses those issues by the following:
    
    - Replace chip->autosuspended boolean flag with chip->system_suspend
      counter
    
    - At the first system-suspend, chip->num_suspended_intf is recorded to
      chip->system_suspend
    
    - At system-resume, the card power state is restored when the
      chip->num_suspended_intf refcount reaches to chip->system_suspend,
      i.e. the state returns to the auto-suspended
    
    Also, the patch fixes yet another hidden problem by the code
    refactoring along with the fixes above: namely, when some resume
    procedure failed, the driver left chip->num_suspended_intf that was
    already decreased, and it might lead to the refcount unbalance.
    In the new code, the refcount decrement is done after the whole resume
    procedure, and the problem is avoided as well.
    
    Fixes: 0662292a
    
     ("ALSA: usb-audio: Handle normal and auto-suspend equally")
    Reported-and-tested-by: default avatarMacpaul Lin <macpaul.lin@mediatek.com>
    Cc: <stable@vger.kernel.org>
    Link: https://lore.kernel.org/r/20200603153709.6293-1-tiwai@suse.de
    
    
    Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
    862b2509