[PATCH v8 0/9] Adjust fbcon console device detection

[PATCH v8 0/9] Adjust fbcon console device detection

[Mario Limonciello]

From: Mario Limonciello <mario.limonciello@amd.com>

This series started out as changes to VGA arbiter to try to handle a case
of a system with 2 GPUs that are not VGA devices.  This was discussed
but decided not to overload the VGA arbiter for non VGA devices.

Instead move the x86 specific detection of framebuffer resources into x86
specific code that the fbcon can use to properly identify the primary
device. This code is still called from the VGA arbiter, and the logic does
not change there. To avoid regression default to VGA arbiter and only fall
back to looking up with x86 specific detection method.

In order for userspace to also be able to discover which device was the
primary video display device create a new sysfs file 'boot_display'.

A matching userspace implementation for this file is available here:
Link: https://gitlab.freedesktop.org/xorg/lib/libpciaccess/-/merge_requests/39
Link: https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2038

Dave Airlie has been pinged for a comment on this approach.
Dave had suggested in the past [1]:

"
 But yes if that doesn't work, then maybe we need to make the boot_vga
 flag mean boot_display_gpu, and fix it in the kernel
"

This was one of the approached tried in earlier revisions and it was
rejected in favor of creating a new sysfs file (which is what this
version does).

It is suggested that this series merge entirely through the PCI tree.

Link: https://gitlab.freedesktop.org/xorg/lib/libpciaccess/-/merge_requests/37#note_2938602 [1]

v8 fixes an LKP robot reported issue

Mario Limonciello (9):
  PCI: Add helper for checking if a PCI device is a display controller
  vfio/pci: Use pci_is_display()
  vga_switcheroo: Use pci_is_display()
  iommu/vt-d: Use pci_is_display()
  ALSA: hda: Use pci_is_display()
  Fix access to video_is_primary_device() when compiled without
    CONFIG_VIDEO
  PCI/VGA: Replace vga_is_firmware_default() with a screen info check
  fbcon: Use screen info to find primary device
  PCI: Add a new 'boot_display' attribute

 Documentation/ABI/testing/sysfs-bus-pci |  8 +++++
 arch/parisc/include/asm/video.h         |  2 +-
 arch/sparc/include/asm/video.h          |  2 ++
 arch/x86/include/asm/video.h            |  2 ++
 arch/x86/video/video-common.c           | 17 ++++++++-
 drivers/gpu/vga/vga_switcheroo.c        |  2 +-
 drivers/iommu/intel/iommu.c             |  2 +-
 drivers/pci/pci-sysfs.c                 | 46 +++++++++++++++++++++++++
 drivers/pci/vgaarb.c                    | 31 +++--------------
 drivers/vfio/pci/vfio_pci_igd.c         |  3 +-
 include/linux/pci.h                     | 15 ++++++++
 sound/hda/hdac_i915.c                   |  2 +-
 sound/pci/hda/hda_intel.c               |  4 +--
 13 files changed, 101 insertions(+), 35 deletions(-)

-- 
2.43.0

[PATCH v8 1/9] PCI: Add helper for checking if a PCI device is a display controller

[Mario Limonciello]

From: Mario Limonciello <mario.limonciello@amd.com>

Several places in the kernel do class shifting to match whether a
PCI device is display class.  Introduce a helper for those places to
use.

Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Daniel Dadap <ddadap@nvidia.com>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
 include/linux/pci.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/include/linux/pci.h b/include/linux/pci.h
index 05e68f35f3923..e77754e43c629 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -744,6 +744,21 @@ static inline bool pci_is_vga(struct pci_dev *pdev)
 	return false;
 }
 
+/**
+ * pci_is_display - Check if a PCI device is a display controller
+ * @pdev: Pointer to the PCI device structure
+ *
+ * This function determines whether the given PCI device corresponds
+ * to a display controller. Display controllers are typically used
+ * for graphical output and are identified based on their class code.
+ *
+ * Return: true if the PCI device is a display controller, false otherwise.
+ */
+static inline bool pci_is_display(struct pci_dev *pdev)
+{
+	return (pdev->class >> 16) == PCI_BASE_CLASS_DISPLAY;
+}
+
 #define for_each_pci_bridge(dev, bus)				\
 	list_for_each_entry(dev, &bus->devices, bus_list)	\
 		if (!pci_is_bridge(dev)) {} else
-- 
2.43.0

[PATCH v8 2/9] vfio/pci: Use pci_is_display()

[Mario Limonciello]

From: Mario Limonciello <mario.limonciello@amd.com>

The inline pci_is_display() helper does the same thing.  Use it.

Acked-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Daniel Dadap <ddadap@nvidia.com>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Suggested-by: Bjorn Helgaas <helgaas@kernel.org>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
 drivers/vfio/pci/vfio_pci_igd.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_igd.c b/drivers/vfio/pci/vfio_pci_igd.c
index ef490a4545f48..988b6919c2c31 100644
--- a/drivers/vfio/pci/vfio_pci_igd.c
+++ b/drivers/vfio/pci/vfio_pci_igd.c
@@ -437,8 +437,7 @@ static int vfio_pci_igd_cfg_init(struct vfio_pci_core_device *vdev)
 
 bool vfio_pci_is_intel_display(struct pci_dev *pdev)
 {
-	return (pdev->vendor == PCI_VENDOR_ID_INTEL) &&
-	       ((pdev->class >> 16) == PCI_BASE_CLASS_DISPLAY);
+	return (pdev->vendor == PCI_VENDOR_ID_INTEL) && pci_is_display(pdev);
 }
 
 int vfio_pci_igd_init(struct vfio_pci_core_device *vdev)
-- 
2.43.0

[PATCH v8 3/9] vga_switcheroo: Use pci_is_display()

[Mario Limonciello]

From: Mario Limonciello <mario.limonciello@amd.com>

The inline pci_is_display() helper does the same thing.  Use it.

Reviewed-by: Daniel Dadap <ddadap@nvidia.com>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Suggested-by: Bjorn Helgaas <helgaas@kernel.org>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
 drivers/gpu/vga/vga_switcheroo.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c
index 18f2c92beff8e..68e45a26e85f7 100644
--- a/drivers/gpu/vga/vga_switcheroo.c
+++ b/drivers/gpu/vga/vga_switcheroo.c
@@ -437,7 +437,7 @@ find_active_client(struct list_head *head)
  */
 bool vga_switcheroo_client_probe_defer(struct pci_dev *pdev)
 {
-	if ((pdev->class >> 16) == PCI_BASE_CLASS_DISPLAY) {
+	if (pci_is_display(pdev)) {
 		/*
 		 * apple-gmux is needed on pre-retina MacBook Pro
 		 * to probe the panel if pdev is the inactive GPU.
-- 
2.43.0

[PATCH v8 4/9] iommu/vt-d: Use pci_is_display()

[Mario Limonciello]

From: Mario Limonciello <mario.limonciello@amd.com>

The inline pci_is_display() helper does the same thing.  Use it.

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Daniel Dadap <ddadap@nvidia.com>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Suggested-by: Bjorn Helgaas <helgaas@kernel.org>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
 drivers/iommu/intel/iommu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 148b944143b81..cad9ed1016cfc 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -34,7 +34,7 @@
 #define ROOT_SIZE		VTD_PAGE_SIZE
 #define CONTEXT_SIZE		VTD_PAGE_SIZE
 
-#define IS_GFX_DEVICE(pdev) ((pdev->class >> 16) == PCI_BASE_CLASS_DISPLAY)
+#define IS_GFX_DEVICE(pdev) pci_is_display(pdev)
 #define IS_USB_DEVICE(pdev) ((pdev->class >> 8) == PCI_CLASS_SERIAL_USB)
 #define IS_ISA_DEVICE(pdev) ((pdev->class >> 8) == PCI_CLASS_BRIDGE_ISA)
 #define IS_AZALIA(pdev) ((pdev)->vendor == 0x8086 && (pdev)->device == 0x3a3e)
-- 
2.43.0

[PATCH v8 5/9] ALSA: hda: Use pci_is_display()

[Mario Limonciello]

From: Mario Limonciello <mario.limonciello@amd.com>

The inline pci_is_display() helper does the same thing.  Use it.

Reviewed-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Daniel Dadap <ddadap@nvidia.com>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Suggested-by: Bjorn Helgaas <helgaas@kernel.org>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
 sound/hda/hdac_i915.c     | 2 +-
 sound/pci/hda/hda_intel.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/sound/hda/hdac_i915.c b/sound/hda/hdac_i915.c
index e9425213320ea..44438c799f957 100644
--- a/sound/hda/hdac_i915.c
+++ b/sound/hda/hdac_i915.c
@@ -155,7 +155,7 @@ static int i915_gfx_present(struct pci_dev *hdac_pci)
 
 	for_each_pci_dev(display_dev) {
 		if (display_dev->vendor != PCI_VENDOR_ID_INTEL ||
-		    (display_dev->class >> 16) != PCI_BASE_CLASS_DISPLAY)
+		    !pci_is_display(display_dev))
 			continue;
 
 		if (pci_match_id(denylist, display_dev))
diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
index 439cf1bda6e66..75badb5c69b8e 100644
--- a/sound/pci/hda/hda_intel.c
+++ b/sound/pci/hda/hda_intel.c
@@ -1465,7 +1465,7 @@ static struct pci_dev *get_bound_vga(struct pci_dev *pci)
 				 * the dGPU is the one who is involved in
 				 * vgaswitcheroo.
 				 */
-				if (((p->class >> 16) == PCI_BASE_CLASS_DISPLAY) &&
+				if (pci_is_display(p) &&
 				    (atpx_present() || apple_gmux_detect(NULL, NULL)))
 					return p;
 				pci_dev_put(p);
@@ -1477,7 +1477,7 @@ static struct pci_dev *get_bound_vga(struct pci_dev *pci)
 			p = pci_get_domain_bus_and_slot(pci_domain_nr(pci->bus),
 							pci->bus->number, 0);
 			if (p) {
-				if ((p->class >> 16) == PCI_BASE_CLASS_DISPLAY)
+				if (pci_is_display(p))
 					return p;
 				pci_dev_put(p);
 			}
-- 
2.43.0

[PATCH v8 6/9] Fix access to video_is_primary_device() when compiled without CONFIG_VIDEO

[Mario Limonciello]

From: Mario Limonciello <mario.limonciello@amd.com>

When compiled without CONFIG_VIDEO the architecture specific
implementations of video_is_primary_device() include prototypes and
assume that video-common.c will be linked. Guard against this so that the
fallback inline implementation that returns false will be used when
compiled without CONFIG_VIDEO.

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202506221312.49Fy1aNA-lkp@intel.com/
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
v5:
 * add tag
v4:
 * new patch
---
 arch/parisc/include/asm/video.h | 2 +-
 arch/sparc/include/asm/video.h  | 2 ++
 arch/x86/include/asm/video.h    | 2 ++
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/parisc/include/asm/video.h b/arch/parisc/include/asm/video.h
index c5dff3223194a..a9d50ebd6e769 100644
--- a/arch/parisc/include/asm/video.h
+++ b/arch/parisc/include/asm/video.h
@@ -6,7 +6,7 @@
 
 struct device;
 
-#if defined(CONFIG_STI_CORE)
+#if defined(CONFIG_STI_CORE) && defined(CONFIG_VIDEO)
 bool video_is_primary_device(struct device *dev);
 #define video_is_primary_device video_is_primary_device
 #endif
diff --git a/arch/sparc/include/asm/video.h b/arch/sparc/include/asm/video.h
index a6f48f52db584..773717b6d4914 100644
--- a/arch/sparc/include/asm/video.h
+++ b/arch/sparc/include/asm/video.h
@@ -19,8 +19,10 @@ static inline pgprot_t pgprot_framebuffer(pgprot_t prot,
 #define pgprot_framebuffer pgprot_framebuffer
 #endif
 
+#ifdef CONFIG_VIDEO
 bool video_is_primary_device(struct device *dev);
 #define video_is_primary_device video_is_primary_device
+#endif
 
 static inline void fb_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
 {
diff --git a/arch/x86/include/asm/video.h b/arch/x86/include/asm/video.h
index 0950c9535fae9..08ec328203ef8 100644
--- a/arch/x86/include/asm/video.h
+++ b/arch/x86/include/asm/video.h
@@ -13,8 +13,10 @@ pgprot_t pgprot_framebuffer(pgprot_t prot,
 			    unsigned long offset);
 #define pgprot_framebuffer pgprot_framebuffer
 
+#ifdef CONFIG_VIDEO
 bool video_is_primary_device(struct device *dev);
 #define video_is_primary_device video_is_primary_device
+#endif
 
 #include <asm-generic/video.h>
 
-- 
2.43.0

[PATCH v8 7/9] PCI/VGA: Replace vga_is_firmware_default() with a screen info check

[Mario Limonciello]

From: Mario Limonciello <mario.limonciello@amd.com>

vga_is_firmware_default() checks firmware resources to find the owner
framebuffer resources to find the firmware PCI device.  This is an
open coded implementation of screen_info_pci_dev().  Switch to using
screen_info_pci_dev() instead.

Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Suggested-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
v6:
 * fix lkp robot error
v5:
 * split from next patch
---
 drivers/pci/vgaarb.c | 31 +++++--------------------------
 1 file changed, 5 insertions(+), 26 deletions(-)

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index 78748e8d2dbae..b58f94ee48916 100644
--- a/drivers/pci/vgaarb.c
+++ b/drivers/pci/vgaarb.c
@@ -556,34 +556,13 @@ EXPORT_SYMBOL(vga_put);
 
 static bool vga_is_firmware_default(struct pci_dev *pdev)
 {
-#if defined(CONFIG_X86)
-	u64 base = screen_info.lfb_base;
-	u64 size = screen_info.lfb_size;
-	struct resource *r;
-	u64 limit;
+#ifdef CONFIG_SCREEN_INFO
+	struct screen_info *si = &screen_info;
 
-	/* Select the device owning the boot framebuffer if there is one */
-
-	if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
-		base |= (u64)screen_info.ext_lfb_base << 32;
-
-	limit = base + size;
-
-	/* Does firmware framebuffer belong to us? */
-	pci_dev_for_each_resource(pdev, r) {
-		if (resource_type(r) != IORESOURCE_MEM)
-			continue;
-
-		if (!r->start || !r->end)
-			continue;
-
-		if (base < r->start || limit >= r->end)
-			continue;
-
-		return true;
-	}
-#endif
+	return pdev == screen_info_pci_dev(si);
+#else
 	return false;
+#endif
 }
 
 static bool vga_arb_integrated_gpu(struct device *dev)
-- 
2.43.0

[PATCH v8 8/9] fbcon: Use screen info to find primary device

[Mario Limonciello]

From: Mario Limonciello <mario.limonciello@amd.com>

On systems with non VGA GPUs fbcon can't find the primary GPU because
video_is_primary_device() only checks the VGA arbiter.

Add a screen info check to video_is_primary_device() so that callers
can get accurate data on such systems.

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Suggested-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
v8:
 * add guards for the non CONFIG_SCREEN_INFO case
v5:
 * Only change video-common.c
v4:
 * use helper
---
 arch/x86/video/video-common.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/x86/video/video-common.c b/arch/x86/video/video-common.c
index 81fc97a2a837a..4bbfffec4b640 100644
--- a/arch/x86/video/video-common.c
+++ b/arch/x86/video/video-common.c
@@ -9,6 +9,7 @@
 
 #include <linux/module.h>
 #include <linux/pci.h>
+#include <linux/screen_info.h>
 #include <linux/vgaarb.h>
 
 #include <asm/video.h>
@@ -27,6 +28,9 @@ EXPORT_SYMBOL(pgprot_framebuffer);
 
 bool video_is_primary_device(struct device *dev)
 {
+#ifdef CONFIG_SCREEN_INFO
+	struct screen_info *si = &screen_info;
+#endif
 	struct pci_dev *pdev;
 
 	if (!dev_is_pci(dev))
@@ -34,7 +38,18 @@ bool video_is_primary_device(struct device *dev)
 
 	pdev = to_pci_dev(dev);
 
-	return (pdev == vga_default_device());
+	if (!pci_is_display(pdev))
+		return false;
+
+	if (pdev == vga_default_device())
+		return true;
+
+#ifdef CONFIG_SCREEN_INFO
+	if (pdev == screen_info_pci_dev(si))
+		return true;
+#endif
+
+	return false;
 }
 EXPORT_SYMBOL(video_is_primary_device);
 
-- 
2.43.0

[PATCH v8 9/9] PCI: Add a new 'boot_display' attribute

[Mario Limonciello]

From: Mario Limonciello <mario.limonciello@amd.com>

On systems with multiple GPUs there can be uncertainty which GPU is the
primary one used to drive the display at bootup. In order to disambiguate
this add a new sysfs attribute 'boot_display' that uses the output of
video_is_primary_device() to populate whether a PCI device was used for
driving the display.

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
v7:
 * fix lkp failure
 * Add tag
v6:
 * Only show for the device that is boot display
 * Only create after PCI device sysfs files are initialized to ensure
   that resources are ready.
v4:
 * new patch
---
 Documentation/ABI/testing/sysfs-bus-pci |  8 +++++
 drivers/pci/pci-sysfs.c                 | 46 +++++++++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 69f952fffec72..8b455b1a58852 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -612,3 +612,11 @@ Description:
 
 		  # ls doe_features
 		  0001:01        0001:02        doe_discovery
+
+What:		/sys/bus/pci/devices/.../boot_display
+Date:		October 2025
+Contact:	Linux PCI developers <linux-pci@vger.kernel.org>
+Description:
+		This file indicates the device was used as a boot
+		display. If the device was used as the boot display, the file
+		will be present and contain "1".
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 268c69daa4d57..6b1a0ae254d3a 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -30,6 +30,7 @@
 #include <linux/msi.h>
 #include <linux/of.h>
 #include <linux/aperture.h>
+#include <asm/video.h>
 #include "pci.h"
 
 #ifndef ARCH_PCI_DEV_GROUPS
@@ -679,6 +680,13 @@ const struct attribute_group *pcibus_groups[] = {
 	NULL,
 };
 
+static ssize_t boot_display_show(struct device *dev, struct device_attribute *attr,
+				 char *buf)
+{
+	return sysfs_emit(buf, "1\n");
+}
+static DEVICE_ATTR_RO(boot_display);
+
 static ssize_t boot_vga_show(struct device *dev, struct device_attribute *attr,
 			     char *buf)
 {
@@ -1051,6 +1059,37 @@ void pci_remove_legacy_files(struct pci_bus *b)
 }
 #endif /* HAVE_PCI_LEGACY */
 
+/**
+ * pci_create_boot_display_file - create a file in sysfs for @dev
+ * @pdev: dev in question
+ *
+ * Creates a file `boot_display` in sysfs for the PCI device @pdev
+ * if it is the boot display device.
+ */
+static int pci_create_boot_display_file(struct pci_dev *pdev)
+{
+#ifdef CONFIG_VIDEO
+	if (video_is_primary_device(&pdev->dev))
+		return sysfs_create_file(&pdev->dev.kobj, &dev_attr_boot_display.attr);
+#endif
+	return 0;
+}
+
+/**
+ * pci_remove_boot_display_file - remove the boot display file for @dev
+ * @pdev: dev in question
+ *
+ * Removes the file `boot_display` in sysfs for the PCI device @pdev
+ * if it is the boot display device.
+ */
+static void pci_remove_boot_display_file(struct pci_dev *pdev)
+{
+#ifdef CONFIG_VIDEO
+	if (video_is_primary_device(&pdev->dev))
+		sysfs_remove_file(&pdev->dev.kobj, &dev_attr_boot_display.attr);
+#endif
+}
+
 #if defined(HAVE_PCI_MMAP) || defined(ARCH_GENERIC_PCI_MMAP_RESOURCE)
 /**
  * pci_mmap_resource - map a PCI resource into user memory space
@@ -1654,9 +1693,15 @@ static const struct attribute_group pci_dev_resource_resize_group = {
 
 int __must_check pci_create_sysfs_dev_files(struct pci_dev *pdev)
 {
+	int retval;
+
 	if (!sysfs_initialized)
 		return -EACCES;
 
+	retval = pci_create_boot_display_file(pdev);
+	if (retval)
+		return retval;
+
 	return pci_create_resource_files(pdev);
 }
 
@@ -1671,6 +1716,7 @@ void pci_remove_sysfs_dev_files(struct pci_dev *pdev)
 	if (!sysfs_initialized)
 		return;
 
+	pci_remove_boot_display_file(pdev);
 	pci_remove_resource_files(pdev);
 }
 
-- 
2.43.0

Re: [PATCH v8 9/9] PCI: Add a new 'boot_display' attribute

[Maxime Ripard]

[-- Attachment #1: Type: text/plain, Size: 1852 bytes --]

Hi Mario,

On Mon, Jul 14, 2025 at 04:21:46PM -0500, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@amd.com>
> 
> On systems with multiple GPUs there can be uncertainty which GPU is the
> primary one used to drive the display at bootup. In order to disambiguate
> this add a new sysfs attribute 'boot_display' that uses the output of
> video_is_primary_device() to populate whether a PCI device was used for
> driving the display.
> 
> Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
> v7:
>  * fix lkp failure
>  * Add tag
> v6:
>  * Only show for the device that is boot display
>  * Only create after PCI device sysfs files are initialized to ensure
>    that resources are ready.
> v4:
>  * new patch
> ---
>  Documentation/ABI/testing/sysfs-bus-pci |  8 +++++
>  drivers/pci/pci-sysfs.c                 | 46 +++++++++++++++++++++++++
>  2 files changed, 54 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> index 69f952fffec72..8b455b1a58852 100644
> --- a/Documentation/ABI/testing/sysfs-bus-pci
> +++ b/Documentation/ABI/testing/sysfs-bus-pci
> @@ -612,3 +612,11 @@ Description:
>  
>  		  # ls doe_features
>  		  0001:01        0001:02        doe_discovery
> +
> +What:		/sys/bus/pci/devices/.../boot_display
> +Date:		October 2025
> +Contact:	Linux PCI developers <linux-pci@vger.kernel.org>
> +Description:
> +		This file indicates the device was used as a boot
> +		display. If the device was used as the boot display, the file
> +		will be present and contain "1".

It would probably be a good idea to define what a "boot display" here
is. I get what you mean, but it's pretty vague and could easily be
misunderstood.

Maxime

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Re: [PATCH v8 9/9] PCI: Add a new 'boot_display' attribute

[Mario Limonciello]

On 7/16/25 3:22 AM, Maxime Ripard wrote:
> Hi Mario,
> 
> On Mon, Jul 14, 2025 at 04:21:46PM -0500, Mario Limonciello wrote:
>> From: Mario Limonciello <mario.limonciello@amd.com>
>>
>> On systems with multiple GPUs there can be uncertainty which GPU is the
>> primary one used to drive the display at bootup. In order to disambiguate
>> this add a new sysfs attribute 'boot_display' that uses the output of
>> video_is_primary_device() to populate whether a PCI device was used for
>> driving the display.
>>
>> Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
>> ---
>> v7:
>>   * fix lkp failure
>>   * Add tag
>> v6:
>>   * Only show for the device that is boot display
>>   * Only create after PCI device sysfs files are initialized to ensure
>>     that resources are ready.
>> v4:
>>   * new patch
>> ---
>>   Documentation/ABI/testing/sysfs-bus-pci |  8 +++++
>>   drivers/pci/pci-sysfs.c                 | 46 +++++++++++++++++++++++++
>>   2 files changed, 54 insertions(+)
>>
>> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
>> index 69f952fffec72..8b455b1a58852 100644
>> --- a/Documentation/ABI/testing/sysfs-bus-pci
>> +++ b/Documentation/ABI/testing/sysfs-bus-pci
>> @@ -612,3 +612,11 @@ Description:
>>   
>>   		  # ls doe_features
>>   		  0001:01        0001:02        doe_discovery
>> +
>> +What:		/sys/bus/pci/devices/.../boot_display
>> +Date:		October 2025
>> +Contact:	Linux PCI developers <linux-pci@vger.kernel.org>
>> +Description:
>> +		This file indicates the device was used as a boot
>> +		display. If the device was used as the boot display, the file
>> +		will be present and contain "1".
> 
> It would probably be a good idea to define what a "boot display" here
> is. I get what you mean, but it's pretty vague and could easily be
> misunderstood.
> 
> Maxime

Here's my proposal for updated text, can you please bikeshed or propose 
an alternative?

This file indicates that displays connected to the device were used to 
display the boot sequence.  If a display connected to the device was
used to display the boot sequence the file will be present and contain "1".

Re: [PATCH v8 0/9] Adjust fbcon console device detection

[Bjorn Helgaas]

On Mon, Jul 14, 2025 at 04:21:37PM -0500, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@amd.com>
> 
> This series started out as changes to VGA arbiter to try to handle a case
> of a system with 2 GPUs that are not VGA devices.  This was discussed
> but decided not to overload the VGA arbiter for non VGA devices.
> 
> Instead move the x86 specific detection of framebuffer resources into x86
> specific code that the fbcon can use to properly identify the primary
> device. This code is still called from the VGA arbiter, and the logic does
> not change there. To avoid regression default to VGA arbiter and only fall
> back to looking up with x86 specific detection method.
> 
> In order for userspace to also be able to discover which device was the
> primary video display device create a new sysfs file 'boot_display'.
> 
> A matching userspace implementation for this file is available here:
> Link: https://gitlab.freedesktop.org/xorg/lib/libpciaccess/-/merge_requests/39
> Link: https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2038
> 
> Dave Airlie has been pinged for a comment on this approach.
> Dave had suggested in the past [1]:
> 
> "
>  But yes if that doesn't work, then maybe we need to make the boot_vga
>  flag mean boot_display_gpu, and fix it in the kernel
> "
> 
> This was one of the approached tried in earlier revisions and it was
> rejected in favor of creating a new sysfs file (which is what this
> version does).
> 
> It is suggested that this series merge entirely through the PCI tree.
> 
> Link: https://gitlab.freedesktop.org/xorg/lib/libpciaccess/-/merge_requests/37#note_2938602 [1]

There's an underlying bug that we're trying to fix with this series
and the related libpciaccess and xserver changes, isn't there?  Can we
include that somewhere to help motivate this?  (I guess it's really
only the last two or three patches that are strictly related, right?)

> v8 fixes an LKP robot reported issue
> 
> Mario Limonciello (9):
>   PCI: Add helper for checking if a PCI device is a display controller
>   vfio/pci: Use pci_is_display()
>   vga_switcheroo: Use pci_is_display()
>   iommu/vt-d: Use pci_is_display()
>   ALSA: hda: Use pci_is_display()
>   Fix access to video_is_primary_device() when compiled without
>     CONFIG_VIDEO
>   PCI/VGA: Replace vga_is_firmware_default() with a screen info check
>   fbcon: Use screen info to find primary device
>   PCI: Add a new 'boot_display' attribute
> 
>  Documentation/ABI/testing/sysfs-bus-pci |  8 +++++
>  arch/parisc/include/asm/video.h         |  2 +-
>  arch/sparc/include/asm/video.h          |  2 ++
>  arch/x86/include/asm/video.h            |  2 ++
>  arch/x86/video/video-common.c           | 17 ++++++++-
>  drivers/gpu/vga/vga_switcheroo.c        |  2 +-
>  drivers/iommu/intel/iommu.c             |  2 +-
>  drivers/pci/pci-sysfs.c                 | 46 +++++++++++++++++++++++++
>  drivers/pci/vgaarb.c                    | 31 +++--------------
>  drivers/vfio/pci/vfio_pci_igd.c         |  3 +-
>  include/linux/pci.h                     | 15 ++++++++
>  sound/hda/hdac_i915.c                   |  2 +-
>  sound/pci/hda/hda_intel.c               |  4 +--
>  13 files changed, 101 insertions(+), 35 deletions(-)
> 
> -- 
> 2.43.0
> 

Re: [PATCH v8 0/9] Adjust fbcon console device detection

[Mario Limonciello]

On 7/16/25 6:23 PM, Bjorn Helgaas wrote:
> On Mon, Jul 14, 2025 at 04:21:37PM -0500, Mario Limonciello wrote:
>> From: Mario Limonciello <mario.limonciello@amd.com>
>>
>> This series started out as changes to VGA arbiter to try to handle a case
>> of a system with 2 GPUs that are not VGA devices.  This was discussed
>> but decided not to overload the VGA arbiter for non VGA devices.
>>
>> Instead move the x86 specific detection of framebuffer resources into x86
>> specific code that the fbcon can use to properly identify the primary
>> device. This code is still called from the VGA arbiter, and the logic does
>> not change there. To avoid regression default to VGA arbiter and only fall
>> back to looking up with x86 specific detection method.
>>
>> In order for userspace to also be able to discover which device was the
>> primary video display device create a new sysfs file 'boot_display'.
>>
>> A matching userspace implementation for this file is available here:
>> Link: https://gitlab.freedesktop.org/xorg/lib/libpciaccess/-/merge_requests/39
>> Link: https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2038
>>
>> Dave Airlie has been pinged for a comment on this approach.
>> Dave had suggested in the past [1]:
>>
>> "
>>   But yes if that doesn't work, then maybe we need to make the boot_vga
>>   flag mean boot_display_gpu, and fix it in the kernel
>> "
>>
>> This was one of the approached tried in earlier revisions and it was
>> rejected in favor of creating a new sysfs file (which is what this
>> version does).
>>
>> It is suggested that this series merge entirely through the PCI tree.
>>
>> Link: https://gitlab.freedesktop.org/xorg/lib/libpciaccess/-/merge_requests/37#note_2938602 [1]
> 
> There's an underlying bug that we're trying to fix with this series
> and the related libpciaccess and xserver changes, isn't there?  Can we
> include that somewhere to help motivate this?  (I guess it's really
> only the last two or three patches that are strictly related, right?)

Do you mean in the cover letter of another spin of the series or just 
inline here?

The issue is that on systems with more than one GPU userspace doesn't 
know which one to be used to treat as primary.  The concept of primary 
is important to be able to decide which GPU is used for display and 
which is used for rendering.  If it's guessed wrong then both GPUs will 
be kept awake burning a lot of power.

Historically it would use the "boot_vga" attribute but this isn't 
present on modern GPUs.  So this series introduces a new attribute to 
give a hint to userspace which was used for display at bootup.  The 
matching patches to libpciaccess and xorg-server utilize this new sysfs 
file to set things up as intended.

And yes, the last few ones are the only ones strictly related to this 
issue. The other patches were just cleanups to use the same new helper 
from these patches elsewhere in the kernel too.

> 
>> v8 fixes an LKP robot reported issue
>>
>> Mario Limonciello (9):
>>    PCI: Add helper for checking if a PCI device is a display controller
>>    vfio/pci: Use pci_is_display()
>>    vga_switcheroo: Use pci_is_display()
>>    iommu/vt-d: Use pci_is_display()
>>    ALSA: hda: Use pci_is_display()
>>    Fix access to video_is_primary_device() when compiled without
>>      CONFIG_VIDEO
>>    PCI/VGA: Replace vga_is_firmware_default() with a screen info check
>>    fbcon: Use screen info to find primary device
>>    PCI: Add a new 'boot_display' attribute
>>
>>   Documentation/ABI/testing/sysfs-bus-pci |  8 +++++
>>   arch/parisc/include/asm/video.h         |  2 +-
>>   arch/sparc/include/asm/video.h          |  2 ++
>>   arch/x86/include/asm/video.h            |  2 ++
>>   arch/x86/video/video-common.c           | 17 ++++++++-
>>   drivers/gpu/vga/vga_switcheroo.c        |  2 +-
>>   drivers/iommu/intel/iommu.c             |  2 +-
>>   drivers/pci/pci-sysfs.c                 | 46 +++++++++++++++++++++++++
>>   drivers/pci/vgaarb.c                    | 31 +++--------------
>>   drivers/vfio/pci/vfio_pci_igd.c         |  3 +-
>>   include/linux/pci.h                     | 15 ++++++++
>>   sound/hda/hdac_i915.c                   |  2 +-
>>   sound/pci/hda/hda_intel.c               |  4 +--
>>   13 files changed, 101 insertions(+), 35 deletions(-)
>>
>> -- 
>> 2.43.0
>>