|DDI_DMA_ALLOC_HANDLE(9F)||Kernel Functions for Drivers||DDI_DMA_ALLOC_HANDLE(9F)|
#include <sys/ddi.h> #include <sys/sunddi.h> int ddi_dma_alloc_handle(dev_info_t *dip, ddi_dma_attr_t *attr, int (*callback) (caddr_t), caddr_t arg, ddi_dma_handle_t *handlep);
The callback function, callback, indicates how a caller wants to handle the possibility of resources not being available. If callback is set to DDI_DMA_DONTWAIT, then the caller does not care if the allocation fails, and can handle an allocation failure appropriately. If callback is set to DDI_DMA_SLEEP, then the caller wishes to have the allocation routines wait for resources to become available. If any other value is set, and a DMA resource allocation fails, this value is assumed to be a function to call at a later time when resources may become available. When the specified function is called, it is passed arg as an argument. The specified callback function must return either DDI_DMA_CALLBACK_RUNOUT or DDI_DMA_CALLBACK_DONE. DDI_DMA_CALLBACK_RUNOUT indicates that the callback routine attempted to allocate DMA resources but failed to do so, in which case the callback function is put back on a list to be called again later. DDI_DMA_CALLBACK_DONE indicates either success at allocating DMA resources or the driver no longer wishes to retry.
The callback function is called in interrupt context. Therefore, only system functions that are accessible from interrupt context is available. The callback function must take whatever steps necessary to protect its critical resources, data structures, queues, and so forth.
When a DMA handle is no longer needed, ddi_dma_free_handle(9F) must be called to free the handle.
Writing Device Drivers
|September 22, 1996||OmniOS|