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.Dd Dec 22, 2016
.Dt USBA_HCDI_PIPE_INTR_XFER 9E
.Os
.Sh NAME
.Nm usba_hcdi_pipe_intr_xfer
.Nd perform a USB interrupt transfer
.Sh SYNOPSIS
.In sys/usb/usba/hcdi.h
.Ft int
.Fo prefix_hcdi_pipe_intr_xfer
.Fa "usba_pipe_handle_data_t *ph"
.Fa "usb_intr_req_t *uirp"
.Fa "usb_flags_t usb_flags"
.Fc
.Sh INTERFACE LEVEL
.Sy Volatile -
illumos USB HCD private function
.Pp
This is a private function that is not part of the stable DDI. It may be
removed or changed at any time.
.Sh PARAMETERS
.Bl -tag -width Fa
.It Fa ph
A pointer to a USB pipe handle as defined in
.Xr usba_pipe_handle_data 9S .
.It Fa uirp
A pointer to a USB interrupt transfer request. The structure's members
are documented in
.Xr usb_intr_req 9S .
.It Fa usb_flags
Flags which describe how allocations should be performed. Valid flags
are:
.Bl -tag -width Sy
.It Sy USB_FLAGS_NOSLEEP
Do not block waiting for memory. If memory is not available the allocation
will fail.
.It Sy USB_FLAGS_SLEEP
Perform a blocking allocation. If memory is not available, the function
will wait until memory is made available.
.Pp
Note, the request may still fail even if
.Sy USB_FLAGS_SLEEP
is specified.
.El
.El
.Sh DESCRIPTION
The
.Fn usba_hcdi_pipe_intr_xfer
entry point is used to initiate an
.Em asynchronous
USB interrupt transfer on the pipe
.Fa ph .
The specific USB interrupt transfer is provided in
.Fa uirp .
For more background on transfer types, see
.Xr usba_hcdi 9E .
.Pp
The host controller driver should first check the USB address of the
pipe handle. It may correspond to the root hub. If it does, rather than
initiating an I/O transfer, the driver may need to emulate it.
.Pp
Unlike other transfers, interrupt transfers may be periodic. If the
transfer is meant to be a one-shot, then the
.Sy USB_ATTRS_ONE_XFER
flag will be set in the
.Sy intr_attributes
member of the
.Fa uirp
structure. If the
.Sy USB_ATTRS_ONE_XFER
flag is not set, then the transfer begins a periodic transfer. Periodic
transfers have different handling and behavior.
.Pp
Interrupt transfers may send data to the device or receive data from the
device. A given interrupt endpoint is uni-directional. The direction can
be determined from the endpoint address based on the
.Sy p_ep
member of
.Fa ubrp .
See
.Xr usb_ep_descr 9S
for more information on how to determine the direction of the endpoint.
.Pp
The device driver should allocate memory, whether memory suitable for a
DMA transfer or otherwise, to perform the transfer. For all memory
allocated, it should honor the values in
.Fa usb_flags
to determine whether or not it should block for allocations.
.Pp
The length of the interrupt transfer and its data can be found in the
.Sy intr_len
and
.Sy intr_data
members of
.Fa uirp
respectively.
 The
.Xr mblk 9S
structure that should not be used directly and data should be copied to
or from the data buffer that will go the controller.
.Pp
Unlike bulk and control transfers, the
.Fa intr_data
member may not be allocated for interrupt-IN transfers. In such cases,
the device driver is required to allocate the message block through
something like
.Xr allocb 9F
and assign it to the
.Sy intr_data
member.
.Pp
If the driver successfully schedules the I/O, then it should return
.Sy USB_SUCCESS .
When the I/O completes, it must call
.Xr usba_hcdi_cb 9F
with
.Fa uirp .
If the transfer fails, but the driver returned
.Sy USB_SUCCESS ,
it still must call
.Xr usba_hcdi_cb 9F
and should specify an error there.
.Pp
It is the driver's responsibility to time out one-shot interrupt transfer
requests. If the timeout in the request as indicated in the
.Sy intr_timeout
member of
.Fa uirp
is set to zero, then the driver should use the USBA default timeout of
.Sy HCDI_DEFAULT_TIMEOUT .
All timeout values are in
.Em seconds .
.Ss Periodic Transfers
When the
.Sy USB_ATTRS_ONE_XFER
flag is not present, it indicates that a periodic interrupt transfer is
being initiated. Once a periodic interrupt transfer is initiated, every
time data is received the driver should call
.Xr usba_hcdi_cb 9F
with the updated data.
.Pp
When a periodic transfer is initiated, many controller drivers will
allocate multiple transfers up front and schedule them all. Many drivers
do this to ensure that data isn't lost between servicing the first
transfer and scheduling the next. The number of such transfers used
depends on the polling frequency specified in the endpoint descriptor.
.Pp
Unless an error occurs, the driver must not use the original interrupt
request,
.Fa uirp .
Instead, it should duplicate the request through the
.Xr usba_hcdi_dup_intr_req 9F
function before calling
.Xr usba_hcdi_cb 9F .
.Pp
The driver should return the original transfer in one of the following
conditions:
.Bl -bullet
.It
A pipe reset request came in from the
.Xr usba_hcdi_pipe_rest 9E
entry point.
.It
A request to stop polling came in from the
.Xr usba_hcdi_pipe_stop_intr_polling 9E
entry point.
.It
A request to close the pipe came in from the
.Xr usba_hcdi_pipe_close 9E
entry point.
.It
An out of memory condition occurred. The caller should call
.Xr usba_hcdi_cb 9F
with the code
.Sy USB_CR_NO_RESOURCES .
.It
Some other transfer error occurred.
.El
.Pp
If the periodic interrupt transfer is for the root hub, the driver will
need to emulate the behavior of a hub as specified in the USB
specification. For more information, see the
.Sx Root Hub Management
section in
.Xr usba_hcdi 9E .
.Ss Callback Handling
When the interrupt transfer completes, the driver should consider the
following items to determine what actions it should take on the
callback:
.Sy USB_SUCCESS .
Otherwise, it should return the appropriate USB error. If uncertain, use
.Sy USB_FAILURE .
.Bl -bullet
.It
If the transfer timed out, it should remove the transfer from the
outstanding list, queue the next transfer, and return the transfer back
to the OS with the error code
.Sy USB_CR_TIMEOUT
with
.Xr usba_hcdi_cb 9F .
.It
If the transfer failed, it should find the appropriate error and call
.Xr usba_hcdi_cb 9F
with that error.
.It
If the transfer succeeded, but less data was transferred than expected,
consult the
.Sy intr_attributes
member of the
.Fa uirp .
If the
.Sy USB_ATTRS_SHORT_XFER_OK
flag is not present, then the driver should call
.Xr usba_hcdi_cb 9F
with the error
.Sy USB_CR_DATA_UNDERRUN .
.It
If the transfer was going to the host, then the driver should copy the
data into the transfer's message block and update the
.Sy b_wptr
member of the
.Xr mblk 9S .
.It
If everything was successful, call
.Xr usba_hcdi_cb 9F
with the code
.Sy USB_CR_OK .
.It
If this was a periodic transfer, it should reschedule the transfer.
.El
.Sh RETURN VALUES
Upon successful completion, the
.Fn usba_hcdi_pipe_intr_xfer
function should return
function should return
.Sy USB_SUCCESS .
Otherwise, it should return the appropriate USB error. If uncertain, use
.Sy USB_FAILURE .
.Sh SEE ALSO
.Xr usba_hcdi 9E ,
.Xr usba_hcdi_pipe_close 9E ,
.Xr usba_hcdi_pipe_rest 9E ,
.Xr usba_hcdi_pipe_stop_intr_polling 9E ,
.Xr allocb 9F ,
.Xr usba_hcdi_cb 9F ,
.Xr usba_hcdi_dup_intr_req 9F ,
.Xr mblk 9S ,
.Xr usb_ep_descr 9S ,
.Xr usb_intr_req 9S ,
.Xr usba_pipe_handle_data 9S