• Hans de Goede's avatar
    pwm: lpss: platform: Save/restore the ctrl register over a suspend/resume · 3c718460
    Hans de Goede authored
    commit 1d375b58 upstream.
    
    On some devices the contents of the ctrl register get lost over a
    suspend/resume and the PWM comes back up disabled after the resume.
    
    This is seen on some Bay Trail devices with the PWM in ACPI enumerated
    mode, so it shows up as a platform device instead of a PCI device.
    
    If we still think it is enabled and then try to change the duty-cycle
    after this, we end up with a "PWM_SW_UPDATE was not cleared" error and
    the PWM is stuck in that state from then on.
    
    This commit adds suspend and resume pm callbacks to the pwm-lpss-platform
    code, which save/restore the ctrl register over a suspend/resume, fixing
    this.
    
    Note that:
    
    1) There is no need to do this over a runtime suspend, since we
    only runtime suspend when disabled and then we properly set the enable
    bit and reprogram the timings when we re-enable the PWM.
    
    2) This may be happening on more systems then we realize, but has been
    covered up sofar by a bug in the acpi-lpss.c code which was save/restoring
    the regular device registers instead of the lpss private registers due to
    lpss_device_desc.prv_offset not being set. This is fixed by a later patch
    in this series.
    
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarHans de Goede <hdegoede@redhat.com>
    Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
    Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    3c718460