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         efi_handle_t *pci_handle __free(efi_pool) = NULL;
  20         unsigned long pci_handle_num;
  21         efi_handle_t handle;
  22         efi_status_t status;
  23         u16 class, command;
  24
  25         status = efi_bs_call(locate_handle_buffer, EFI_LOCATE_BY_PROTOCOL,
  26                              &pci_proto, NULL, &pci_handle_num, &pci_handle);
  27         if (status != EFI_SUCCESS) {
  28                 efi_err("Failed to locate PCI I/O handles\n");
  29                 return;
  30         }
  31
  32         for_each_efi_handle(handle, pci_handle, pci_handle_num) {
  33                 efi_pci_io_protocol_t *pci;
  34                 unsigned long segment_nr, bus_nr, device_nr, func_nr;
  35
  36                 status = efi_bs_call(handle_protocol, handle, &pci_proto,
  37                                      (void **)&pci);
  38                 if (status != EFI_SUCCESS)
  39                         continue;
  40
  41                 /*
  42                  * Disregard devices living on bus 0 - these are not behind a
  43                  * bridge so no point in disconnecting them from their drivers.
  44                  */
  45                 status = efi_call_proto(pci, get_location, &segment_nr, &bus_nr,
  46                                         &device_nr, &func_nr);
  47                 if (status != EFI_SUCCESS || bus_nr == 0)
  48                         continue;
  49
  50                 /*
  51                  * Don't disconnect VGA controllers so we don't risk losing
  52                  * access to the framebuffer. Drivers for true PCIe graphics
  53                  * controllers that are behind a PCIe root port do not use
  54                  * DMA to implement the GOP framebuffer anyway [although they
  55                  * may use it in their implementation of Gop->Blt()], and so
  56                  * disabling DMA in the PCI bridge should not interfere with
  57                  * normal operation of the device.
  58                  */
  59                 status = efi_call_proto(pci, pci.read, EfiPciIoWidthUint16,
  60                                         PCI_CLASS_DEVICE, 1, &class);
  61                 if (status != EFI_SUCCESS || class == PCI_CLASS_DISPLAY_VGA)
  62                         continue;
  63
  64                 /* Disconnect this handle from all its drivers */
  65                 efi_bs_call(disconnect_controller, handle, NULL, NULL);
  66         }
  67
  68         for_each_efi_handle(handle, pci_handle, pci_handle_num) {
  69                 efi_pci_io_protocol_t *pci;
  70
  71                 status = efi_bs_call(handle_protocol, handle, &pci_proto,
  72                                      (void **)&pci);
  73                 if (status != EFI_SUCCESS || !pci)
  74                         continue;
  75
  76                 status = efi_call_proto(pci, pci.read, EfiPciIoWidthUint16,
  77                                         PCI_CLASS_DEVICE, 1, &class);
  78
  79                 if (status != EFI_SUCCESS || class != PCI_CLASS_BRIDGE_PCI)
  80                         continue;
  81
  82                 /* Disable busmastering */
  83                 status = efi_call_proto(pci, pci.read, EfiPciIoWidthUint16,
  84                                         PCI_COMMAND, 1, &command);
  85                 if (status != EFI_SUCCESS || !(command & PCI_COMMAND_MASTER))
  86                         continue;
  87
  88                 command &= ~PCI_COMMAND_MASTER;
  89                 status = efi_call_proto(pci, pci.write, EfiPciIoWidthUint16,
  90                                         PCI_COMMAND, 1, &command);
  91                 if (status != EFI_SUCCESS)
  92                         efi_err("Failed to disable PCI busmastering\n");
  93         }
  94 }