.\" Copyright (c) IBM Corp. 2015
.\" Author: Alexey Ishchuk <aishchuk@linux.vnet.ibm.com>
.\"
.\" SPDX-License-Identifier: GPL-2.0-or-later
.\"
.TH s390_pci_mmio_write 2 2023-03-30 "Linux man-pages 6.04"
.SH NAME
s390_pci_mmio_write, s390_pci_mmio_read \- transfer data to/from PCI
MMIO memory page
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.BR "#include <sys/syscall.h>" "      /* Definition of " SYS_* " constants */"
.B #include <unistd.h>
.PP
.BI "int syscall(SYS_s390_pci_mmio_write, unsigned long " mmio_addr ,
.BI "                       const void " user_buffer [. length "], \
size_t " length );
.BI "int syscall(SYS_s390_pci_mmio_read, unsigned long " mmio_addr ,
.BI "                       void " user_buffer [. length "], size_t " length );
.fi
.PP
.IR Note :
glibc provides no wrappers for these system calls,
necessitating the use of
.BR syscall (2).
.SH DESCRIPTION
The
.BR s390_pci_mmio_write ()
system call writes
.I length
bytes of data from the user-space buffer
.I user_buffer
to the PCI MMIO memory location specified by
.IR mmio_addr .
The
.BR s390_pci_mmio_read ()
system call reads
.I length
bytes of
data from the PCI MMIO memory location specified by
.I mmio_addr
to the user-space buffer
.IR user_buffer .
.PP
These system calls must be used instead of the simple assignment
or data-transfer operations that are used to access the PCI MMIO
memory areas mapped to user space on the Linux System z platform.
The address specified by
.I mmio_addr
must belong to a PCI MMIO memory page mapping in the caller's address space,
and the data being written or read must not cross a page boundary.
The
.I length
value cannot be greater than the system page size.
.SH RETURN VALUE
On success,
.BR s390_pci_mmio_write ()
and
.BR s390_pci_mmio_read ()
return 0.
On failure, \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EFAULT
The address in
.I mmio_addr
is invalid.
.TP
.B EFAULT
.I user_buffer
does not point to a valid location in the caller's address space.
.TP
.B EINVAL
Invalid
.I length
argument.
.TP
.B ENODEV
PCI support is not enabled.
.TP
.B ENOMEM
Insufficient memory.
.SH STANDARDS
Linux on s390.
.SH HISTORY
Linux 3.19.
System z EC12.
.SH SEE ALSO
.BR syscall (2)