Re: [PATCH 5/5] Add DMA engine driver for Freescale MPC85xx processors.

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Dan Williams wrote:

This routine implies that there is a piece of code somewhere that
wants to select which channels it can use.  A similar effect can be
achieved by registering a dma_client with the dmaengine interface
('dma_async_client_register').  Then when the client code makes a call
to 'dma_async_client_chan_request' it receives a 'dma_event_callback'
for each channel in the system.  It will also be asynchronously
notified of channels entering and leaving the system.  The goal is to
share a common infrastructure for channel management.

Are you familiar with the "flat device tree" used for PowerPC systems? The "piece of code somewhere" is the device tree subsystem that parses the device tree, which is compiled from the .dts files in arch/powerpc/boot/dts.

The FDT is how PowerPC systems specify hardware configuration. In the case of 85xx, the FDT contains entries for each DMA device (typically 2), and the entries contain sub-entries for each DMA channel as well as the address of the register sets for each channel.

--
Timur Tabi
Linux Kernel Developer @ Freescale
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