drivers/firmware/efi/libstub/pci.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * PCI-related functions used by the EFI stub on multiple
   4  * architectures.
   5  *
   6  * Copyright 2019 Google, LLC
   7  */
   8
   9 #include <linux/efi.h>
  10 #include <linux/pci.h>
  11
  12 #include <asm/efi.h>
  13
  14 #include "efistub.h"
  15
  16 void efi_pci_disable_bridge_busmaster(void)
  17 {
  18         efi_guid_t pci_proto = EFI_PCI_IO_PROTOCOL_GUID;
  19         unsigned long pci_handle_size = 0;
  20         efi_handle_t *pci_handle = NULL;
  21         efi_handle_t handle;
  22         efi_status_t status;
  23         u16 class, command;
  24         int i;
  25
  26         status = efi_bs_call(locate_handle, EFI_LOCATE_BY_PROTOCOL, &pci_proto,
  27                              NULL, &pci_handle_size, NULL);
  28
  29         if (status != EFI_BUFFER_TOO_SMALL) {
  30                 if (status != EFI_SUCCESS && status != EFI_NOT_FOUND)
  31                         efi_err("Failed to locate PCI I/O handles'\n");
  32                 return;
  33         }
  34
  35         status = efi_bs_call(allocate_pool, EFI_LOADER_DATA, pci_handle_size,
  36                              (void **)&pci_handle);
  37         if (status != EFI_SUCCESS) {
  38                 efi_err("Failed to allocate memory for 'pci_handle'\n");
  39                 return;
  40         }
  41
  42         status = efi_bs_call(locate_handle, EFI_LOCATE_BY_PROTOCOL, &pci_proto,
  43                              NULL, &pci_handle_size, pci_handle);
  44         if (status != EFI_SUCCESS) {
  45                 efi_err("Failed to locate PCI I/O handles'\n");
  46                 goto free_handle;
  47         }
  48
  49         for_each_efi_handle(handle, pci_handle, pci_handle_size, i) {
  50                 efi_pci_io_protocol_t *pci;
  51                 unsigned long segment_nr, bus_nr, device_nr, func_nr;
  52
  53                 status = efi_bs_call(handle_protocol, handle, &pci_proto,
  54                                      (void **)&pci);
  55                 if (status != EFI_SUCCESS)
  56                         continue;
  57
  58                 /*
  59                  * Disregard devices living on bus 0 - these are not behind a
  60                  * bridge so no point in disconnecting them from their drivers.
  61                  */
  62                 status = efi_call_proto(pci, get_location, &segment_nr, &bus_nr,
  63                                         &device_nr, &func_nr);
  64                 if (status != EFI_SUCCESS || bus_nr == 0)
  65                         continue;
  66
  67                 /*
  68                  * Don't disconnect VGA controllers so we don't risk losing
  69                  * access to the framebuffer. Drivers for true PCIe graphics
  70                  * controllers that are behind a PCIe root port do not use
  71                  * DMA to implement the GOP framebuffer anyway [although they
  72                  * may use it in their implementation of Gop->Blt()], and so
  73                  * disabling DMA in the PCI bridge should not interfere with
  74                  * normal operation of the device.
  75                  */
  76                 status = efi_call_proto(pci, pci.read, EfiPciIoWidthUint16,
  77                                         PCI_CLASS_DEVICE, 1, &class);
  78                 if (status != EFI_SUCCESS || class == PCI_CLASS_DISPLAY_VGA)
  79                         continue;
  80
  81                 /* Disconnect this handle from all its drivers */
  82                 efi_bs_call(disconnect_controller, handle, NULL, NULL);
  83         }
  84
  85         for_each_efi_handle(handle, pci_handle, pci_handle_size, i) {
  86                 efi_pci_io_protocol_t *pci;
  87
  88                 status = efi_bs_call(handle_protocol, handle, &pci_proto,
  89                                      (void **)&pci);
  90                 if (status != EFI_SUCCESS || !pci)
  91                         continue;
  92
  93                 status = efi_call_proto(pci, pci.read, EfiPciIoWidthUint16,
  94                                         PCI_CLASS_DEVICE, 1, &class);
  95
  96                 if (status != EFI_SUCCESS || class != PCI_CLASS_BRIDGE_PCI)
  97                         continue;
  98
  99                 /* Disable busmastering */
 100                 status = efi_call_proto(pci, pci.read, EfiPciIoWidthUint16,
 101                                         PCI_COMMAND, 1, &command);
 102                 if (status != EFI_SUCCESS || !(command & PCI_COMMAND_MASTER))
 103                         continue;
 104
 105                 command &= ~PCI_COMMAND_MASTER;
 106                 status = efi_call_proto(pci, pci.write, EfiPciIoWidthUint16,
 107                                         PCI_COMMAND, 1, &command);
 108                 if (status != EFI_SUCCESS)
 109                         efi_err("Failed to disable PCI busmastering\n");
 110         }
 111
 112 free_handle:
 113         efi_bs_call(free_pool, pci_handle);
 114 }