xdma_channel.h

linux嵌入式系统的dma方式的实现代码

/* $Id: xdma_channel.h,v 1.6 2006/07/18 17:56:33 xduan Exp $ */
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/**
*
* @file xdma_channel.h
*
* <b>Description</b>
*
* This file contains the DMA channel component implementation. This component
* supports a distributed DMA design in which each device can have it's own
* dedicated DMA channel, as opposed to a centralized DMA design.
* A device which uses DMA typically contains two DMA channels, one for
* sending data and the other for receiving data.
*
* This component is designed to be used as a basic building block for
* designing a device driver. It provides registers accesses such that all
* DMA processing can be maintained easier, but the device driver designer
* must still understand all the details of the DMA channel.
*
* The DMA channel allows a CPU to minimize the CPU interaction required to move
* data between a memory and a device.  The CPU requests the DMA channel to
* perform a DMA operation and typically continues performing other processing
* until the DMA operation completes.  DMA could be considered a primitive form
* of multiprocessing such that caching and address translation can be an issue.
*
* <b>Scatter Gather Operations</b>
*
* The DMA channel may support scatter gather operations. A scatter gather
* operation automates the DMA channel such that multiple buffers can be
* sent or received with minimal software interaction with the hardware.  Buffer
* descriptors, contained in the XBufDescriptor component, are used by the
* scatter gather operations of the DMA channel to describe the buffers to be
* processed.
*
* <b>Scatter Gather List Operations</b>
*
* A scatter gather list may be supported by each DMA channel.  The scatter
* gather list allows buffer descriptors to be put into the list by a device
* driver which requires scatter gather.  The hardware processes the buffer
* descriptors which are contained in the list and modifies the buffer
* descriptors to reflect the status of the DMA operations.  The device driver
* is notified by interrupt that specific DMA events occur including scatter
* gather events.  The device driver removes the completed buffer descriptors
* from the scatter gather list to evaluate the status of each DMA operation.
*
* The scatter gather list is created and buffer descriptors are inserted into
* the list.  Buffer descriptors are never removed from the list after it's
* creation such that a put operation copies from a temporary buffer descriptor
* to a buffer descriptor in the list.  Get operations don't copy from the list
* to a temporary, but return a pointer to the buffer descriptor in the list.
* A buffer descriptor in the list may be locked to prevent it from being
* overwritten by a put operation.  This allows the device driver to get a
* descriptor from a scatter gather list and prevent it from being overwritten
* until the buffer associated with the buffer descriptor has been processed.
*
* <b>Typical Scatter Gather Processing</b>
*
* The following steps illustrate the typical processing to use the
* scatter gather features of a DMA channel.
*
* 1. Create a scatter gather list for the DMA channel which puts empty buffer
*    descriptors into the list.<br>
* 2. Create buffer descriptors which describe the buffers to be filled with
*       receive data or the buffers which contain data to be sent.<br>
* 3. Put buffer descriptors into the DMA channel scatter list such that scatter
*    gather operations are requested.<br>
* 4. Commit the buffer descriptors in the list such that they are ready to be
*    used by the DMA channel hardware.<br>
* 5. Start the scatter gather operations of the DMA channel.<br>
* 6. Process any interrupts which occur as a result of the scatter gather
*    operations or poll the DMA channel to determine the status.
*
* <b>Interrupts</b>
*
* Each DMA channel has the ability to generate an interrupt.  This component
* does not perform processing for the interrupt as this processing is typically
* tightly coupled with the device which is using the DMA channel.  It is the
* responsibility of the caller of DMA functions to manage the interrupt
* including connecting to the interrupt and enabling/disabling the interrupt.
*
* <b>Critical Sections</b>
*
* It is the responsibility of the device driver designer to use critical
* sections as necessary when calling functions of the DMA channel.  This
* component does not use critical sections and it does access registers using
* read-modify-write operations.  Calls to DMA functions from a main thread
* and from an interrupt context could produce unpredictable behavior such that
* the caller must provide the appropriate critical sections.
*
* <b>Address Translation</b>
*
* All addresses of data structures which are passed to DMA functions must
* be physical (real) addresses as opposed to logical (virtual) addresses.
*
* <b>Caching</b>
*
* The memory which is passed to the function which creates the scatter gather
* list must not be cached such that buffer descriptors are non-cached.  This
* is necessary because the buffer descriptors are kept in a ring buffer and
* not directly accessible to the caller of DMA functions.
*
* The caller of DMA functions is responsible for ensuring that any data
* buffers which are passed to the DMA channel are cache-line aligned if
* necessary.
*
* The caller of DMA functions is responsible for ensuring that any data
* buffers which are passed to the DMA channel have been flushed from the cache.
*
* The caller of DMA functions is responsible for ensuring that the cache is
* invalidated prior to using any data buffers which are the result of a DMA
* operation.
*
* <b>Memory Alignment</b>
*
* The addresses of data buffers which are passed to DMA functions must be
* 32 bit word aligned since the DMA hardware performs 32 bit word transfers.
*
* <b>Mutual Exclusion</b>
*
* The functions of the DMA channel are not thread safe such that the caller
* of all DMA functions is responsible for ensuring mutual exclusion for a
* DMA channel.  Mutual exclusion across multiple DMA channels is not
* necessary.
*
* @note
*
* Many of the provided functions which are register accessors don't provide
* a lot of error detection. The caller is expected to understand the impact
* of a function call based upon the current state of the DMA channel.  This
* is done to minimize the overhead in this component.
*
* <pre>
* MODIFICATION HISTORY:
*
* Ver   Who  Date     Changes
* ----- ---- -------- -----------------------------------------------
* 1.00a xd   10/27/04 Doxygenated for inclusion in API documentation
* 1.00b ecm  10/31/05 Updated for the check sum offload changes.
* 1.00b xd   03/22/06 Fixed a multi-descriptor packet related bug that sgdma
*                     engine is restarted in case no scatter gather disabled
*                     bit is set yet
* </pre>
*
******************************************************************************/

#ifndef XDMA_CHANNEL_H    /* prevent circular inclusions */
#define XDMA_CHANNEL_H    /* by using protection macros */

#ifdef __cplusplus
extern "C" {
#endif

/***************************** Include Files *********************************/

#include "xbasic_types.h"