powerpc/pseries: Add papr-hvpipe char driver for HVPIPE interfaces

The hypervisor provides ibm,send-hvpipe-msg and
ibm,receive-hvpipe-msg RTAS calls which can be used by the
partition to communicate through an inband hypervisor channel with
different external sources such as Hardware Management Console
(HMC). The information exchanged, whether it be messages, raw or
formatted data, etc., is only known to between applications in the
OS and the source (HMC). This patch adds papr-hvpipe character
driver and provides the standard interfaces such as open / ioctl/
read / write to user space for exchanging information with HMC
using send/recevive HVPIPE RTAS functions.

PAPR (7.3.32 Hypervisor Pipe Information Exchange) defines the
HVPIPE usage:
- The hypervisor has one HVPIPE per partition for all sources.
- OS can determine this feature’s availability by detecting the
  “ibm,hypervisor-pipe-capable” property in the /rtas node of the
  device tree.
- Each source is represented by the source ID which is used in
  send / recv HVPIPE RTAS. (Ex: source ID is the target for the
  payload in send RTAS).
- Return status of ibm,send-hvpipe-msg can be considered as
  delivered the payload.
- Return status of ibm,receive-hvpipe-msg can be considered as
  ACK to source.
- The hypervisor generates hvpipe message event interrupt when
  the partition has the payload to receive.

Provide the interfaces to the user space with /dev/papr-hvpipe
character device using the following programming model:

int devfd = open("/dev/papr-hvpipe")
int fd = ioctl(devfd, PAPR_HVPIPE_IOC_CREATE_HANDLE, &srcID);
- Restrict the user space to use the same source ID and do not
  expect more than one process access with the same source.
char *buf = malloc(size);
- SIZE should be 4K and the buffer contains header and the
  payload.
length = write(fd, buf, size);
- OS issues ibm,send-hvpipe-msg RTAS and returns the RTAS status
  to the user space.
ret = poll(fd,...)
- The HVPIPE event message IRQ wakes up for any waiting FDs.
length = read(fd, buf, size);
- OS issues ibm,receive-hvpipe-msg to receive payload from the
  hypervisor.
release(fd);
- OS issues ibm,receive-hvpipe-msg if any payload is pending so
  that pipe is not blocked.

The actual implementation of these calls are added in the
next patches.

Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Tested-by: Shashank MS <shashank.gowda@in.ibm.com>
Reviewed-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Reviewed-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250909084402.1488456-4-haren@linux.ibm.com

0 files changed, 0 insertions, 0 deletions