• Andy Shevchenko's avatar
    dma: acpi-dma: introduce ACPI DMA helpers · 1b2e98bc
    Andy Shevchenko authored
    There is a new generic API to get a DMA channel for a slave device (commit
    9a6cecc8 "dmaengine: add helper function to request a slave DMA channel"). In
    similar fashion to the DT case (commit aa3da644 "of: Add generic device tree
    DMA helpers") we introduce helpers to the DMAC drivers which are enumerated by
    ACPI.
    
    The proposed extension provides the following API calls:
    	acpi_dma_controller_register(), devm_acpi_dma_controller_register()
    	acpi_dma_controller_free(), devm_acpi_dma_controller_free()
    	acpi_dma_simple_xlate()
    	acpi_dma_request_slave_chan_by_index()
    	acpi_dma_request_slave_chan_by_name()
    
    The first two should be used, for example, at probe() and remove() of the
    corresponding DMAC driver. At the register stage the DMAC driver supplies a
    custom xlate() function to translate a struct dma_spec into struct dma_chan.
    
    Accordingly to the ACPI Fixed DMA resource specification the only two pieces of
    information the slave device has are the channel id and the request line (slave
    id). Those two are represented by struct dma_spec. The
    acpi_dma_request_slave_chan_by_index() provides access to the specifix FixedDMA
    resource by its index. Whereas dma_request_slave_channel() takes a string
    parameter to identify the DMA resources required by the slave device. To make a
    slave device driver work with both DeviceTree and ACPI enumeration a simple
    convention is established: "tx" corresponds to the index 0 and "rx" to the
    index 1. In case of robust configuration the slave device driver unfortunately
    needs to call acpi_dma_request_slave_chan_by_index() directly.
    
    Additionally the patch provides "managed" version of the register/free pair
    i.e. devm_acpi_dma_controller_register() and devm_acpi_dma_controller_free().
    Usually, the driver uses only devm_acpi_dma_controller_register().
    Signed-off-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
    Reviewed-by: default avatarMika Westerberg <mika.westerberg@linux.intel.com>
    Acked-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: default avatarVinod Koul <vinod.koul@intel.com>
    1b2e98bc
acpi-dma.c 7.47 KB