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Merged
SnowCheetos merged 1 commit into from
Aug 26, 2026
Merged

drivers/gop: Resolve GOP child controller ownership #2

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11 changes: 7 additions & 4 deletions EXTENSIONS.md
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,10 @@ For `LIMINE_MP_FRAMEBUFFER_SOURCE_UNKNOWN`, `data` is `NULL`. For
segment-group numbering. Values outside the PCI ranges are never reported as a
PCI source.

UEFI GOP handles are resolved through their device paths to the closest handle
supporting `EFI_PCI_IO_PROTOCOL`, whose `GetLocation()` method provides the PCI
coordinates. Resolution failure, a non-PCI provider, and BIOS VBE all produce
an unknown source rather than an inferred identity.
UEFI GOP handles are first resolved through their device paths to the closest
handle supporting `EFI_PCI_IO_PROTOCOL`. If firmware installs GOP on a child
whose device path cannot be resolved to PCI I/O, the loader accepts only an
explicit `EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER` relationship naming that GOP
handle. The selected PCI I/O protocol's `GetLocation()` method provides the PCI
coordinates. Failure of both positive relationships, a non-PCI provider, and
BIOS VBE all produce an unknown source rather than an inferred identity.
109 changes: 90 additions & 19 deletions common/drivers/gop.c
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Original file line number Diff line number Diff line change
Expand Up @@ -131,27 +131,14 @@ static bool mode_to_fb_info(struct fb_info *ret, EFI_GRAPHICS_OUTPUT_PROTOCOL *g

bool gop_force_16 = false;

static void get_framebuffer_source(struct fb_info *fb, EFI_HANDLE gop_handle) {
EFI_GUID device_path_guid = EFI_DEVICE_PATH_PROTOCOL_GUID;
EFI_DEVICE_PATH *device_path = NULL;

EFI_STATUS status = gBS->HandleProtocol(gop_handle, &device_path_guid,
(void **)&device_path);
if (status != EFI_SUCCESS) {
return;
}

static bool set_pci_framebuffer_source(struct fb_info *fb,
EFI_HANDLE pci_handle) {
EFI_GUID pci_io_guid = EFI_PCI_IO_PROTOCOL_GUID;
EFI_HANDLE pci_handle = NULL;
status = gBS->LocateDevicePath(&pci_io_guid, &device_path, &pci_handle);
if (status != EFI_SUCCESS) {
return;
}

EFI_PCI_IO_PROTOCOL *pci_io = NULL;
status = gBS->HandleProtocol(pci_handle, &pci_io_guid, (void **)&pci_io);
EFI_STATUS status = gBS->HandleProtocol(pci_handle, &pci_io_guid,
(void **)&pci_io);
if (status != EFI_SUCCESS) {
return;
return false;
}

UINTN segment;
Expand All @@ -164,7 +151,7 @@ static void get_framebuffer_source(struct fb_info *fb, EFI_HANDLE gop_handle) {
|| bus > UINT8_MAX
|| device > 31
|| function > 7) {
return;
return false;
}

fb->source_type = FB_SOURCE_PCI;
Expand All @@ -176,6 +163,90 @@ static void get_framebuffer_source(struct fb_info *fb, EFI_HANDLE gop_handle) {
printv("gop: Framebuffer source PCI %x:%x:%x.%x\n",
(uint32_t)segment, (uint32_t)bus, (uint32_t)device,
(uint32_t)function);
return true;
}

static bool get_framebuffer_source_from_device_path(struct fb_info *fb,
EFI_HANDLE gop_handle) {
EFI_GUID device_path_guid = EFI_DEVICE_PATH_PROTOCOL_GUID;
EFI_DEVICE_PATH *device_path = NULL;

EFI_STATUS status = gBS->HandleProtocol(gop_handle, &device_path_guid,
(void **)&device_path);
if (status != EFI_SUCCESS) {
return false;
}

EFI_GUID pci_io_guid = EFI_PCI_IO_PROTOCOL_GUID;
EFI_HANDLE pci_handle = NULL;
status = gBS->LocateDevicePath(&pci_io_guid, &device_path, &pci_handle);
return status == EFI_SUCCESS
&& set_pci_framebuffer_source(fb, pci_handle);
}

static bool pci_handle_owns_gop_child(EFI_HANDLE pci_handle,
EFI_GUID *pci_io_guid,
EFI_HANDLE gop_handle) {
EFI_OPEN_PROTOCOL_INFORMATION_ENTRY *entries = NULL;
UINTN entries_count = 0;
EFI_STATUS status = gBS->OpenProtocolInformation(pci_handle, pci_io_guid,
&entries, &entries_count);
if (status != EFI_SUCCESS) {
return false;
}

bool owns = false;
for (UINTN i = 0; i < entries_count; i++) {
if ((entries[i].Attributes & EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER)
&& entries[i].ControllerHandle == gop_handle) {
owns = true;
break;
}
}
if (entries != NULL) {
gBS->FreePool(entries);
}
return owns;
}

static void get_framebuffer_source(struct fb_info *fb, EFI_HANDLE gop_handle) {
if (get_framebuffer_source_from_device_path(fb, gop_handle)) {
return;
}

// Some firmware installs GOP on a child handle whose device path cannot be
// resolved back to EFI_PCI_IO_PROTOCOL. UEFI bus drivers still record the
// controller relationship by opening the parent PCI I/O protocol with
// EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER and the GOP handle as
// ControllerHandle. Walk only those explicit relationships: guessing from
// framebuffer addresses or display class would not prove boot ownership.
EFI_GUID pci_io_guid = EFI_PCI_IO_PROTOCOL_GUID;
EFI_HANDLE tmp_handles[1];
EFI_HANDLE *handles = tmp_handles;
UINTN handles_size = sizeof(tmp_handles);
EFI_STATUS status = gBS->LocateHandle(ByProtocol, &pci_io_guid, NULL,
&handles_size, handles);
if (status != EFI_SUCCESS && status != EFI_BUFFER_TOO_SMALL) {
return;
}

UINTN handles_alloc = handles_size;
handles = ext_mem_alloc(handles_alloc);
status = gBS->LocateHandle(ByProtocol, &pci_io_guid, NULL,
&handles_size, handles);
if (status != EFI_SUCCESS) {
pmm_free(handles, handles_alloc);
return;
}

size_t handles_count = handles_size / sizeof(EFI_HANDLE);
for (size_t i = 0; i < handles_count; i++) {
if (pci_handle_owns_gop_child(handles[i], &pci_io_guid, gop_handle)
&& set_pci_framebuffer_source(fb, handles[i])) {
break;
}
}
pmm_free(handles, handles_alloc);
}

static bool try_mode(struct fb_info *ret, EFI_GRAPHICS_OUTPUT_PROTOCOL *gop,
Expand Down
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