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| Data Structures for Drivers | ddi_device_acc_attr(9S) |
| | ddi_device_acc_attr - data access attributes structure |
SYNOPSIS
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#include <sys/ddi.h>
#include <sys/sunddi.h>
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Solaris DDI specific (Solaris DDI).
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The ddi_device_acc_attr structure describes the data access characteristics and requirements of the device.
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ushort_t devacc_attr_version;
uchar_t devacc_attr_endian_flags;
uchar_t devacc_attr_dataorder;
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The devacc_attr_version member identifies the version number of this structure. The current version number is DDI_DEVICE_ATTR_V0.
The devacc_attr_endian_flags member describes the endian characteristics of the device. Specify one of the following values:
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DDI_NEVERSWAP_ACC
- Data access with no byte swapping
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DDI_STRUCTURE_BE_ACC
- Structural data access in big-endian format
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DDI_STRUCTURE_LE_ACC
- Structural data access in little endian format
DDI_STRUCTURE_BE_ACC and DDI_STRUCTURE_LE_ACC describes the endian characteristics of the device as big-endian or little-endian, respectively. Though most of the devices will have the same endian characteristics
as their buses, examples of devices that have opposite endian characteristics of the buses do exist. When DDI_STRUCTURE_BE_ACC or DDI_STRUCTURE_LE_ACC is set, byte swapping is automatically performed by the system if the
host machine and the device data formats have opposite endian characteristics. The implementation can take advantage of hardware platform byte swapping capabilities.
When you specify DDI_NEVERSWAP_ACC, byte swapping is not invoked in the data access functions.
The devacc_attr_dataorder member describes order in which the CPU will reference data. Specify one of the following values.
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DDI_STRICTORDER_ACC
- The data references must be issued by a CPU in program order. Strict ordering is the default behavior.
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DDI_UNORDERED_OK_ACC
- The CPU can re-order the data references. This includes all kinds of re-ordering. For example, a load followed by a store may be replaced by a store followed
by a load.
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DDI_MERGING_OK_ACC
- The CPU can merge individual stores to consecutive locations. For example, the CPU can turn two consecutive byte stores
into one halfword store. It can also batch individual loads. For example, the CPU might turn two consecutive byte loads into one halfword load. DDI_MERGING_OK_ACC also implies re-ordering.
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DDI_LOADCACHING_OK_ACC
- The CPU can cache the data it fetches and reuse it until another store occurs. The default behavior is to fetch new data on every load. DDI_LOADCACHING_OK_ACC also implies merging and re-ordering.
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DDI_STORECACHING_OK_ACC
- The CPU can keep the data in the cache and push it to the device (perhaps with other data) at a later time. The default behavior is to push the data
right away. DDI_STORECACHING_OK_ACC also implies load caching, merging, and re-ordering.
These values are advisory, not mandatory. For example, data can be ordered without being merged or cached, even though a driver requests unordered, merged, and cached together.
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The following examples illustrate the use of device register address mapping setup functions and different data access functions. Example 1. Using ddi_device_acc_attr in ddi_regs_map_setup9F
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This example demonstrates the use of the ddi_device_acc_attr() structure in ddi_regs_map_setup(9F). It also shows the use
of ddi_getw(9F) and ddi_putw(9F)
functions in accessing the register contents.
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dev_info_t *dip;
uint_t rnumber;
ushort_t *dev_addr;
offset_t offset;
offset_t len;
ushort_t dev_command;
ddi_device_acc_attr_t dev_attr;
ddi_acc_handle_t handle;
...
/*
* setup the device attribute structure for little endian,
* strict ordering and 16-bit word access.
*/
dev_attr.devacc_attr_version = DDI_DEVICE_ATTR_V0;
dev_attr.devacc_attr_endian_flags = DDI_STRUCTURE_LE_ACC;
dev_attr.devacc_attr_dataorder = DDI_STRICTORDER_ACC;
/*
* set up the device registers address mapping
*/
ddi_regs_map_setup(dip, rnumber, (caddr_t *)&dev_addr, offset, len,
&dev_attr, &handle);
/* read a 16-bit word command register from the device */
dev_command = ddi_getw(handle, dev_addr);
dev_command |= DEV_INTR_ENABLE;
/* store a new value back to the device command register */
ddi_putw(handle, dev_addr, dev_command);
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Example 2. Accessing a Device with Different Apertures
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The following example illustrates the steps used to access a device with different apertures. Several apertures are assumed to be grouped under one single "reg" entry. For example, the sample device has four different apertures, each 32 Kbyte in size. The apertures represent YUV
little-endian, YUV big-endian, RGB little-endian, and RGB big-endian. This sample device uses entry 1 of the "reg" property list for this purpose. The size of the address space is 128 Kbyte with each 32 Kbyte range as a separate aperture. In the
register mapping setup function, the sample driver uses the offset and len parameters to specify one of the apertures.
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ulong_t *dev_addr;
ddi_device_acc_attr_t dev_attr;
ddi_acc_handle_t handle;
uchar_t buf[256];
...
/*
* setup the device attribute structure for never swap,
* unordered and 32-bit word access.
*/
dev_attr.devacc_attr_version = DDI_DEVICE_ATTR_V0;
dev_attr.devacc_attr_endian_flags = DDI_NEVERSWAP_ACC;
dev_attr.devacc_attr_dataorder = DDI_UNORDERED_OK_ACC;
/*
* map in the RGB big-endian aperture
* while running in a big endian machine
* - offset 96K and len 32K
*/
ddi_regs_map_setup(dip, 1, (caddr_t *)&dev_addr, 96*1024, 32*1024,
&dev_attr, &handle);
/*
* Write to the screen buffer
* first 1K bytes words, each size 4 bytes
*/
ddi_rep_putl(handle, buf, dev_addr, 256, DDI_DEV_AUTOINCR);
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Example 3. Functions That Call Out the Data Word Size
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The following example illustrates the use of the functions that explicitly call out the data word size to override the data size in the device attribute structure.
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struct device_blk {
ushort_t d_command; /* command register */
ushort_t d_status; /* status register */
ulong d_data; /* data register */
} *dev_blkp;
dev_info_t *dip;
caddr_t dev_addr;
ddi_device_acc_attr_t dev_attr;
ddi_acc_handle_t handle;
uchar_t buf[256];
...
/*
* setup the device attribute structure for never swap,
* strict ordering and 32-bit word access.
*/
dev_attr.devacc_attr_version = DDI_DEVICE_ATTR_V0;
dev_attr.devacc_attr_endian_flags = DDI_NEVERSWAP_ACC;
dev_attr.devacc_attr_dataorder= DDI_STRICTORDER_ACC;
ddi_regs_map_setup(dip, 1, (caddr_t *)&dev_blkp, 0, 0,
&dev_attr, &handle);
/* write command to the 16-bit command register */
ddi_putw(handle, &dev_blkp->d_command, START_XFER);
/* Read the 16-bit status register */
status = ddi_getw(handle, &dev_blkp->d_status);
if (status & DATA_READY)
/* Read 1K bytes off the 32-bit data register */
ddi_rep_getl(handle, buf, &dev_blkp->d_data,
256, DDI_DEV_NO_AUTOINCR);
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