github.com/mvdan/u-root-coreutils@v0.0.0-20230122170626-c2eef2898555/cmds/core/io/smn.go (about)

     1  // Copyright 2020 the u-root Authors. All rights reserved
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build amd64 && linux
     6  // +build amd64,linux
     7  
     8  // The System Management Network (SMN, try to say it fast)
     9  // is a parallel universe address space on newer AMD64 cpus.
    10  // The address is 32 bits, as is data.
    11  // Unfortunately it is only accessible via the classic
    12  // index/register pair. Fortunately that pair is accessible
    13  // in mmconfig space.
    14  package main
    15  
    16  import (
    17  	"github.com/mvdan/u-root-coreutils/pkg/memio"
    18  )
    19  
    20  type op func() error
    21  
    22  // This is a const at present but there are no guarantees.
    23  const pcibase = 0xe0000000
    24  
    25  func init() {
    26  	usageMsg += `io rs index # read from system management network on newer AMD CPUs.
    27  io ws index value # write value to system management network on newer AMD CPUs.
    28  `
    29  	addCmd(readCmds, "rs", &cmd{smnRead, 32, 32})
    30  	addCmd(writeCmds, "ws", &cmd{smnWrite, 32, 32})
    31  }
    32  
    33  func do(addr int64, data memio.UintN, op func(int64, memio.UintN) error) error {
    34  	a := newInt(uint64(addr), 32)
    35  	if err := memio.Write(pcibase+0xb8, a); err != nil {
    36  		return err
    37  	}
    38  	return op(pcibase+0xbc, data)
    39  }
    40  
    41  func smnWrite(addr int64, data memio.UintN) error {
    42  	return do(addr, data, memio.Write)
    43  }
    44  
    45  func smnRead(addr int64, data memio.UintN) error {
    46  	return do(addr, data, memio.Read)
    47  }