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'\" te .\" Copyright (c) 2005, 2016, Oracle and/or its affiliates. All rights reserved. .TH ddi_dma_req 9S "10 Nov 2016" "Oracle Solaris 11.4" "Kernel & Driver Data Structures" .SH NAME ddi_dma_req \- DMA Request structure .SH SYNOPSIS .LP .nf #include <sys/ddidmareq.h> .fi .SH INTERFACE LEVEL .sp .LP Solaris DDI specific (Solaris DDI). This interface is obsolete. .SH DESCRIPTION .sp .LP A \fBddi_dma_req\fR structure describes a request for \fBDMA\fR resources. A driver can use it to describe forms of allocations and ways to allocate \fBDMA\fR resources for a \fBDMA\fR request. .SH STRUCTURE MEMBERS .sp .in +2 .nf ddi_dma_lim_t *dmar_limits; /* Caller's dma engine constraints */ uint_t dmar_flags; /* Contains info for mapping routines */ int (*dmar_fp)(caddr_t);/* Callback function */ caddr_t dmar_arg; /* Callback function's argument */ ddi_dma_obj_t dmar_object; /* Descrip. of object to be mapped */ .fi .in -2 .sp .sp .LP For the definition of the \fBDMA\fR limits structure, which \fBdmar_limits\fR points to, see \fBddi_dma_lim_sparc\fR(9S) or \fBddi_dma_lim_x86\fR(9S). .sp .LP Valid values for \fBdmar_flags\fR are: .sp .in +2 .nf DDI_DMA_WRITE /* Direction memory --> IO */ DDI_DMA_READ /* Direction IO --> memory */ DDI_DMA_RDWR /* Both read and write */ DDI_DMA_REDZONE /* Establish MMU redzone at end of mapping */ DDI_DMA_PARTIAL /* Partial mapping is allowed */ DDI_DMA_CONSISTENT /* Byte consistent access wanted */ DDI_DMA_SBUS_64BIT /* Use 64 bit capability on SBus */ .fi .in -2 .sp .sp .LP \fBDDI_DMA_WRITE\fR, \fBDDI_DMA_READ\fR, and \fBDDI_DMA_RDWR\fR describe the intended direction of the \fBDMA \fRtransfer. Some implementations might explicitly disallow \fBDDI_DMA_RDWR\fR. .sp .LP \fBDDI_DMA_REDZONE\fR asks the system to establish a protected \fBred zone\fR after the object. The \fBDMA\fR resource allocation functions do not guarantee the success of this request, as some implementations might not have the hardware ability to support it. .sp .LP \fBDDI_DMA_PARTIAL\fR lets the system know that the caller can accept partial mapping. That is, if the size of the object exceeds the resources available, the system allocates only a portion of the object and returns status indicating this partial allocation. At a later point, the caller can use \fBddi_dma_curwin\fR(9F) and \fBddi_dma_movwin\fR(9F) to change the valid portion of the object that has resources allocated. .sp .LP \fBDDI_DMA_CONSISTENT\fR gives a hint to the system that the object should be mapped for \fBbyte consistent\fR access. Normal data transfers usually use a \fBstreaming\fR mode of operation. They start at a specific point, transfer a fairly large amount of data sequentially, and then stop, usually on an aligned boundary. Control mode data transfers for memory-resident device control blocks (for example, Ethernet message descriptors) do not access memory in such a sequential fashion. Instead, they tend to modify a few words or bytes, move around and maybe modify a few more. .sp .LP Many machine implementations make this non-sequential memory access difficult to control in a generic and seamless fashion. Therefore, explicit synchronization steps using \fBddi_dma_sync\fR(9F) or \fBddi_dma_free\fR(9F) are required to make the view of a memory object shared between a \fBCPU \fRand a \fBDMA\fR device consistent. However, proper use of the \fBDDI_DMA_CONSISTENT\fR flag can create a condition in which a system will pick resources in a way that makes these synchronization steps are as efficient as possible. .sp .LP \fBDDI_DMA_SBUS_64BIT\fR tells the system that the device can perform 64-bit transfers on a 64-bit SBus. If the SBus does not support 64-bit data transfers, data will be transferred in 32-bit mode. .sp .LP The callback function specified by the member \fBdmar_fp\fR indicates how a caller to one of the \fBDMA\fR resource allocation functions wants to deal with the possibility of resources not being available. (See \fBddi_dma_setup\fR(9F).) If \fBdmar_fp\fR is set to \fBDDI_DMA_DONTWAIT\fR, then the caller does not care if the allocation fails, and can deal with an allocation failure appropriately. Setting \fBdmar_fp\fR to \fBDDI_DMA_SLEEP\fR indicates the caller wants to have the allocation routines wait for resources to become available. If any other value is set, and a \fBDMA\fR resource allocation fails, this value is assumed to be a function to call later, when resources become available. When the specified function is called, it is passed the value set in the structure member \fBdmar_arg\fR. The specified callback function \fBmust\fR return either: .sp .ne 2 .mk .na \fB\fB0\fR\fR .ad .RS 5n .rt Indicating that it attempted to allocate a \fBDMA\fR resource but failed to do so, again, in which case the callback function will be put back on a list to be called again later. .RE .sp .ne 2 .mk .na \fB\fB1\fR\fR .ad .RS 5n .rt Indicating either success at allocating \fBDMA\fR resources or that it no longer wants to retry. .RE .sp .LP The callback function is called in interrupt context. Therefore, only system functions and contexts that are accessible from interrupt context are available. The callback function must take whatever steps necessary to protect its critical resources, data structures, and queues. .sp .LP It is possible that a call to \fBddi_dma_free\fR(9F), which frees \fBDMA\fR resources, might cause a callback function to be called and, unless some care is taken, an undesired recursion can occur. This can cause an undesired recursive \fBmutex_enter\fR(9F), which makes the system panic. .SS "dmar_object Structure" .sp .LP The \fBdmar_object\fR member of the \fBddi_dma_req\fR structure is itself a complex and extensible structure: .sp .in +2 .nf uint_t dmao_size; /* size, in bytes, of the object */ ddi_dma_atyp_t dmao_type; /* type of object */ ddi_dma_aobj_t dmao_obj; /* the object described */ .fi .in -2 .sp .sp .LP The \fBdmao_size\fR element is the size, in bytes, of the object resources allocated for \fBDMA\fR. .sp .LP The \fBdmao_type\fR element selects the kind of object described by \fBdmao_obj\fR. It can be set to \fBDMA_OTYP_VADDR\fR, indicating virtual addresses. .sp .LP The last element, \fBdmao_obj\fR, consists of the virtual address type: .sp .in +2 .nf struct v_address virt_obj; .fi .in -2 .sp .sp .LP It is specified as: .sp .in +2 .nf struct v_address { caddr_t v_addr; /* base virtual address */ struct as *v_as; /* pointer to address space */ void *v_priv; /* priv data for shadow I/O */ }; .fi .in -2 .sp .SH ATTRIBUTES .sp .LP See \fBattributes\fR(7) for descriptions of the following attributes: .sp .TS tab( ) box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) . ATTRIBUTE TYPE ATTRIBUTE VALUE _ Interface Stability Obsolete .TE .sp .SH SEE ALSO .sp .LP \fBddi_dma_addr_setup\fR(9F), \fBddi_dma_buf_setup\fR(9F), \fBddi_dma_curwin\fR(9F), \fBddi_dma_free\fR(9F), \fBddi_dma_movwin\fR(9F), \fBddi_dma_setup\fR(9F), \fBddi_dma_sync\fR(9F), \fBdmao_get_size\fR(9F), \fBmutex\fR(9F) .sp .LP \fIWriting Device Drivers in Oracle Solaris 11.4\fR