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Copyright 2014 Garrett D'Amore <garrett@damore.org>
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ddi_check_acc_handle, ddi_check_dma_handle - Check data access and DMA handles

#include <sys/ddi.h>
#include <sys/sunddi.h>



int ddi_check_acc_handle(ddi_acc_handle_t  acc_handle );

int ddi_check_dma_handle(ddi_dma_handle_t dma_handle );

illumos DDI specific (illumos DDI) acc_handle dma_handle The ddi_check_acc_handle() and ddi_check_dma_handle() functions check for faults that can interfere with communication between a driver and the device it controls. Each function checks a single handle of a specific type and returns a status value indicating whether faults affecting the resource mapped by the supplied handle have been detected.

If a fault is indicated when checking a data access handle, this implies that the driver is no longer able to access the mapped registers or memory using programmed I/O through that handle. Typically, this might occur after the device has failed to respond to an I/O access (for example, has incurred a bus error or timed out). The effect of programmed I/O accesses made after this happens is undefined; for example, read accesses (for example, ddi_get8(9F)) may return random values, and write accesses (for example, ddi_put8(9F)) may or may not have any effect. This type of fault is normally fatal to the operation of the device, and the driver should report it via ddi_dev_report_fault(9F) specifying DDI_SERVICE_LOST for the impact, and DDI_DATAPATH_FAULT for the location.

If a fault is indicated when checking a DMA handle, it implies that a fault has been detected that has (or will) affect DMA transactions between the device and the memory currently bound to the handle (or most recently bound, if the handle is currently unbound). Possible causes include the failure of a component in the DMA data path, or an attempt by the device to make an invalid DMA access. The driver may be able to continue by falling back to a non-DMA mode of operation, but in general, DMA faults are non-recoverable. The contents of the memory currently (or previously) bound to the handle should be regarded as indeterminate. The fault indication associated with the current transaction is lost once the handle is (re-)bound, but because the fault may persist, future DMA operations may not succeed.

Note that some implementations cannot detect all types of failure. If a fault is not indicated, this does not constitute a guarantee that communication is possible. However, if a check fails, this is a positive indication that a problem does exist with respect to communication using that handle.

The ddi_check_acc_handle() and ddi_check_dma_handle() functions return DDI_SUCCESS if no faults affecting the supplied handle are detected and DDI_FAILURE if any fault affecting the supplied handle is detected.

static int
xxattach(dev_info_t *dip, ddi_attach_cmd_t cmd)
{
 ...
 /* This driver uses only a single register-access handle */
 status = ddi_regs_map_setup(dip, REGSET_ZERO, &regaddr,
 0, 0, , &acc_attrs, &acc_hdl);
 if (status != DDI_SUCCESS)
 return (DDI_FAILURE);
 ...
}

static int
xxread(dev_t dev, struct uio *uio_p, cred_t *cred_p)
{
 ...
 if (ddi_check_acc_handle(acc_hdl) != DDI_SUCCESS) {
 ddi_dev_report_fault(dip, DDI_SERVICE_LOST,
 DDI_DATAPATH_FAULT, "register access fault during read");
 return (EIO);
 }
 ...

The ddi_check_acc_handle() and ddi_check_dma_handle() functions may be called from user, kernel, or interrupt context. ddi_dev_report_fault (9F), ddi_dma_alloc_handle (9F), ddi_get8 (9F), ddi_put8 (9F), ddi_regs_map_setup (9F)