FreeBSD/Linux Kernel Cross Reference
sys/contrib/device-tree/Bindings/sound/fsl,ssi.txt

     Freescale Synchronous Serial Interface
     
     The SSI is a serial device that communicates with audio codecs.  It can
     be programmed in AC97, I2S, left-justified, or right-justified modes.
     
     Required properties:
     - compatible:       Compatible list, should contain one of the following
                         compatibles:
                           fsl,mpc8610-ssi
                          fsl,imx51-ssi
                          fsl,imx35-ssi
                          fsl,imx21-ssi
    - cell-index:       The SSI, <0> = SSI1, <1> = SSI2, and so on.
    - reg:              Offset and length of the register set for the device.
    - interrupts:       <a b> where a is the interrupt number and b is a
                        field that represents an encoding of the sense and
                        level information for the interrupt.  This should be
                        encoded based on the information in section 2)
                        depending on the type of interrupt controller you
                        have.
    - fsl,fifo-depth:   The number of elements in the transmit and receive FIFOs.
                        This number is the maximum allowed value for SFCSR[TFWM0].
     - clocks:          "ipg" - Required clock for the SSI unit
                        "baud" - Required clock for SSI master mode. Otherwise this
                          clock is not used
    
    Required are also ac97 link bindings if ac97 is used. See
    Documentation/devicetree/bindings/sound/soc-ac97link.txt for the necessary
    bindings.
    
    Optional properties:
    - codec-handle:     Phandle to a 'codec' node that defines an audio
                        codec connected to this SSI.  This node is typically
                        a child of an I2C or other control node.
    - fsl,fiq-stream-filter: Bool property. Disabled DMA and use FIQ instead to
                        filter the codec stream. This is necessary for some boards
                        where an incompatible codec is connected to this SSI, e.g.
                        on pca100 and pcm043.
    - dmas:             Generic dma devicetree binding as described in
                        Documentation/devicetree/bindings/dma/dma.txt.
    - dma-names:        Two dmas have to be defined, "tx" and "rx", if fsl,imx-fiq
                        is not defined.
    - fsl,mode:         The operating mode for the AC97 interface only.
                        "ac97-slave" - AC97 mode, SSI is clock slave
                        "ac97-master" - AC97 mode, SSI is clock master
    - fsl,ssi-asynchronous:
                        If specified, the SSI is to be programmed in asynchronous
                        mode.  In this mode, pins SRCK, STCK, SRFS, and STFS must
                        all be connected to valid signals.  In synchronous mode,
                        SRCK and SRFS are ignored.  Asynchronous mode allows
                        playback and capture to use different sample sizes and
                        sample rates.  Some drivers may require that SRCK and STCK
                        be connected together, and SRFS and STFS be connected
                        together.  This would still allow different sample sizes,
                        but not different sample rates.
    - fsl,playback-dma: Phandle to a node for the DMA channel to use for
                        playback of audio.  This is typically dictated by SOC
                        design.  See the notes below.
                        Only used on Power Architecture.
    - fsl,capture-dma:  Phandle to a node for the DMA channel to use for
                        capture (recording) of audio.  This is typically dictated
                        by SOC design.  See the notes below.
                        Only used on Power Architecture.
    
    Child 'codec' node required properties:
    - compatible:       Compatible list, contains the name of the codec
    
    Child 'codec' node optional properties:
    - clock-frequency:  The frequency of the input clock, which typically comes
                        from an on-board dedicated oscillator.
    
    Notes on fsl,playback-dma and fsl,capture-dma:
    
    On SOCs that have an SSI, specific DMA channels are hard-wired for playback
    and capture.  On the MPC8610, for example, SSI1 must use DMA channel 0 for
    playback and DMA channel 1 for capture.  SSI2 must use DMA channel 2 for
    playback and DMA channel 3 for capture.  The developer can choose which
    DMA controller to use, but the channels themselves are hard-wired.  The
    purpose of these two properties is to represent this hardware design.
    
    The device tree nodes for the DMA channels that are referenced by
    "fsl,playback-dma" and "fsl,capture-dma" must be marked as compatible with
    "fsl,ssi-dma-channel".  The SOC-specific compatible string (e.g.
    "fsl,mpc8610-dma-channel") can remain.  If these nodes are left as
    "fsl,elo-dma-channel" or "fsl,eloplus-dma-channel", then the generic Elo DMA
    drivers (fsldma) will attempt to use them, and it will conflict with the
    sound drivers.

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