Adjust fbcon console device detection

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 <[email protected]>

Suggested-by Thomas Zimmermann <[email protected]>

Signed-off-by Mario Limonciello (AMD) <[email protected]>

---
v10:
* Rebase on 6.17-rc1

---
  drivers/pci/vgaarb.c | 31 +++++--------------------------
  1 file changed, 5 insertions(+), 26 deletions(-)

drivers/pci/vgaarb.c +5 -26

index 78748e8d2dbae..b58f94ee48916 100644
@@ -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)

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 <[email protected]>

Suggested-by Thomas Zimmermann <[email protected]>

Signed-off-by Mario Limonciello (AMD) <[email protected]>

Hi,

Quoted 8 lines · Mario Limonciello (AMD)

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 <[email protected]>

Suggested-by Thomas Zimmermann <[email protected]>

Signed-off-by Mario Limonciello (AMD) <[email protected]>

I'm getting a black screen on boot on mainline, and it bisected to this commit. Reverting this commit fixed it.

Please revert.

- Eric

Quoted 12 lines · Eric Biggers

Hi,

Quoted 8 lines · Mario Limonciello (AMD)

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 <[email protected]>

Suggested-by Thomas Zimmermann <[email protected]>

Signed-off-by Mario Limonciello (AMD) <[email protected]>

Quoted 6 lines

I'm getting a black screen on boot on mainline, and it bisected to this commit. Reverting this commit fixed it.

Please revert.

- Eric

Can you please share more information about your issue before we jump straight into a revert? What kind of hardware do you have? Perhaps a kernel log from mainline and another from mainline with the revert could help identify what's going on?

A revert might be the right solution, but I would rather fix the issue if it's plausible to do so.

Quoted 22 lines · Mario Limonciello

Quoted 12 lines · Eric Biggers

Hi,

Quoted 8 lines · Mario Limonciello (AMD)

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 <[email protected]>

Suggested-by Thomas Zimmermann <[email protected]>

Signed-off-by Mario Limonciello (AMD) <[email protected]>

Quoted 6 lines

I'm getting a black screen on boot on mainline, and it bisected to this commit. Reverting this commit fixed it.

Please revert.

- Eric

Quoted 7 lines

Can you please share more information about your issue before we jump straight into a revert? What kind of hardware do you have? Perhaps a kernel log from mainline and another from mainline with the revert could help identify what's going on?

A revert might be the right solution, but I would rather fix the issue if it's plausible to do so.

Relevant hardware is:
AMD Ryzen 9 9950X 16-Core Processor
Radeon RX 9070

The following message appears in the good log but not the bad log:

fbcon: amdgpudrmfb (fb0) is primary device

I don't have CONFIG_SCREEN_INFO enabled, so the commit changed vga_is_firmware_default() to always return false.

If DRM_AMDGPU depends on SCREEN_INFO now, it needs to select it.

- Eric

Quoted 2 lines

I don't have CONFIG_SCREEN_INFO enabled, so the commit changed vga_is_firmware_default() to always return false.

Thanks, that definitely explains it.

Quoted 4 lines

If DRM_AMDGPU depends on SCREEN_INFO now, it needs to select it.

- Eric

Well the question now is which driver should actually select it.

Although it manifested for you in amdgpu, I don't think this is going to be an amdgpu unique issue.

Maybe this:

drivers/video/fbdev/core/Kconfig +0 -0

index 006638eefa41..ce2544924b0e 100644
@@ -5,6 +5,7 @@
 

 config FB_CORE
        select VIDEO
+       select SCREEN_INFO

tristate

 config FB_NOTIFY

Quoted 5 lines · Mario Limonciello (AMD)

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.

Quoted 3 lines

Acked-by Bjorn Helgaas <[email protected]>

Suggested-by Thomas Zimmermann <[email protected]>

Signed-off-by Mario Limonciello (AMD) <[email protected]>

I'm getting a black screen on boot on mainline, and it bisected to this commit. Reverting this commit fixed it.

Quoted 10 lines · Eric Biggers

Quoted 8 lines · Mario Limonciello (AMD)

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 <[email protected]>

Suggested-by Thomas Zimmermann <[email protected]>

Signed-off-by Mario Limonciello (AMD) <[email protected]>

Quoted 2 lines

I'm getting a black screen on boot on mainline, and it bisected to this commit. Reverting this commit fixed it.

#regzbot introduced: 337bf13aa9dd ("PCI/VGA: Replace vga_is_firmware_default() with a screen info check") #regzbot link: https://lore.kernel.org/r/[email protected]

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 <[email protected]>

Suggested-by Thomas Zimmermann <[email protected]>

Suggested-by Bjorn Helgaas <[email protected]>

Signed-off-by Mario Limonciello (AMD) <[email protected]>

---
v10:
* Rebase on 6.17-rc1
* Squash 'fbcon: Stop using screen_info_pci_dev()'

---
 arch/x86/video/video-common.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

arch/x86/video/video-common.c +24 -1

index 81fc97a2a837a..e0aeee99bc99e 100644
@@ -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 +28,11 @@ EXPORT_SYMBOL(pgprot_framebuffer);
 
 bool video_is_primary_device(struct device *dev)
 {
+#ifdef CONFIG_SCREEN_INFO
+	struct screen_info *si = &screen_info;
+	struct resource res[SCREEN_INFO_MAX_RESOURCES];
+	ssize_t i, numres;
+#endif
 	struct pci_dev *pdev;
 
 	if (!dev_is_pci(dev))

@@ -34,7 +40,24 @@ 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
+	numres = screen_info_resources(si, res, ARRAY_SIZE(res));
+	for (i = 0; i < numres; ++i) {
+		if (!(res[i].flags & IORESOURCE_MEM))
+			continue;
+
+		if (pci_find_resource(pdev, &res[i]))
+			return true;
+	}
+#endif
+
+	return false;
 }
 EXPORT_SYMBOL(video_is_primary_device);
 

Signature · 1 line

2.43.0

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 <[email protected]>

Suggested-by Thomas Zimmermann <[email protected]>

Suggested-by Bjorn Helgaas <[email protected]>

Signed-off-by Mario Limonciello (AMD) <[email protected]>

---
v10:
* Rebase on 6.17-rc1
* Squash 'fbcon: Stop using screen_info_pci_dev()'

---
 arch/x86/video/video-common.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

arch/x86/video/video-common.c +6 -0

index 81fc97a2a837a..e0aeee99bc99e 100644
@@ -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 +28,11 @@ EXPORT_SYMBOL(pgprot_framebuffer);
 
 bool video_is_primary_device(struct device *dev)
 {
+#ifdef CONFIG_SCREEN_INFO
+	struct screen_info *si = &screen_info;
+	struct resource res[SCREEN_INFO_MAX_RESOURCES];
+	ssize_t i, numres;
+#endif
 	struct pci_dev *pdev;
 
 	if (!dev_is_pci(dev))

Quoted 5 lines · Mario Limonciello (AMD)

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.

I have a question regarding this change. To me, the function name video_is_primary_device() implies that there is only one primary GPU. I would also expect that the 'boot_display' attribute added later in the patch series based on this function is only set for one GPU, but that is not necessarily the case. Since I'm working on a user-space program that reads the 'boot_display' attribute, I need to know what behavior is intended in order to do a correct implementation.

Quoted 38 lines

Reviewed-by Thomas Zimmermann <[email protected]>

Suggested-by Thomas Zimmermann <[email protected]>

Suggested-by Bjorn Helgaas <[email protected]>

Signed-off-by Mario Limonciello (AMD) <[email protected]>

---
v10:
* Rebase on 6.17-rc1
* Squash 'fbcon: Stop using screen_info_pci_dev()'

---
  arch/x86/video/video-common.c | 25 ++++++++++++++++++++++++-
  1 file changed, 24 insertions(+), 1 deletion(-)

arch/x86/video/video-common.c +6 -0

index 81fc97a2a837a..e0aeee99bc99e 100644
@@ -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 +28,11 @@ EXPORT_SYMBOL(pgprot_framebuffer);
 
  bool video_is_primary_device(struct device *dev)
  {
+#ifdef CONFIG_SCREEN_INFO
+	struct screen_info *si = &screen_info;
+	struct resource res[SCREEN_INFO_MAX_RESOURCES];
+	ssize_t i, numres;
+#endif
  	struct pci_dev *pdev;
 
  	if (!dev_is_pci(dev))

arch/x86/video/video-common.c bool video_is_primary_device(struct device *dev) · line 47

Quoted 9 lines

arch/x86/video/video-common.c +5 -1

@@ -34,7 +40,24 @@ 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;

This can mark a VGA device as primary GPU.

arch/x86/video/video-common.c bool video_is_primary_device(struct device *dev) · line 58

Quoted 11 lines

arch/x86/video/video-common.c +11 -0

+
+#ifdef CONFIG_SCREEN_INFO
+	numres = screen_info_resources(si, res, ARRAY_SIZE(res));
+	for (i = 0; i < numres; ++i) {
+		if (!(res[i].flags & IORESOURCE_MEM))
+			continue;
+
+		if (pci_find_resource(pdev, &res[i]))
+			return true;
+	}
+#endif

And then the new code can also choose a primary GPU.

arch/x86/video/video-common.c bool video_is_primary_device(struct device *dev) · line 63

Quoted 5 lines

arch/x86/video/video-common.c +2 -0

+
+	return false;
  }
  EXPORT_SYMBOL(video_is_primary_device);
 

In particular, I have hardware that has this exact configuration where two GPUs are marked as primary and have a 'boot_display' attribute: the first one through vga_default_device(), the second one through the new detection method.

Is this intended?

Kind regards
Aaron

Quoted 51 lines · Mario Limonciello (AMD)

Quoted 5 lines

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.

I have a question regarding this change. To me, the function name video_is_primary_device() implies that there is only one primary GPU. I would also expect that the 'boot_display' attribute added later in the patch series based on this function is only set for one GPU, but that is not necessarily the case. Since I'm working on a user-space program that reads the 'boot_display' attribute, I need to know what behavior is intended in order to do a correct implementation.

Quoted 35 lines

Reviewed-by Thomas Zimmermann <[email protected]>

Suggested-by Thomas Zimmermann <[email protected]>

Suggested-by Bjorn Helgaas <[email protected]>

Signed-off-by Mario Limonciello (AMD) <[email protected]>

---
v10:
  * Rebase on 6.17-rc1
  * Squash 'fbcon: Stop using screen_info_pci_dev()'
---
  arch/x86/video/video-common.c | 25 ++++++++++++++++++++++++-

  1 file changed, 24 insertions(+), 1 deletion(-)

arch/x86/video/video-common.c +6 -0

index 81fc97a2a837a..e0aeee99bc99e 100644
@@ -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 +28,11 @@ EXPORT_SYMBOL(pgprot_framebuffer);
     bool video_is_primary_device(struct device *dev)
   {
+#ifdef CONFIG_SCREEN_INFO
+    struct screen_info *si = &screen_info;
+    struct resource res[SCREEN_INFO_MAX_RESOURCES];
+    ssize_t i, numres;
+#endif
       struct pci_dev *pdev;
         if (!dev_is_pci(dev))

@@ -34,7 +40,24 @@ bool video_is_primary_device(struct device *dev)
         pdev = to_pci_dev(dev);

Quoted 8 lines

arch/x86/video/video-common.c bool video_is_primary_device(struct device *dev) · line 47

Quoted 6 lines

arch/x86/video/video-common.c +5 -0

   -    return (pdev == vga_default_device());
+    if (!pci_is_display(pdev))
+        return false;
+
+    if (pdev == vga_default_device())
+        return true;

This can mark a VGA device as primary GPU.

Quoted 14 lines

arch/x86/video/video-common.c bool video_is_primary_device(struct device *dev) · line 58

Quoted 12 lines

arch/x86/video/video-common.c +11 -0

+
+#ifdef CONFIG_SCREEN_INFO
+    numres = screen_info_resources(si, res, ARRAY_SIZE(res));
+    for (i = 0; i < numres; ++i) {
+        if (!(res[i].flags & IORESOURCE_MEM))
+            continue;
+
+        if (pci_find_resource(pdev, &res[i]))
+            return true;
+    }
+#endif

And then the new code can also choose a primary GPU.

Quoted 11 lines

arch/x86/video/video-common.c bool video_is_primary_device(struct device *dev) · line 62

Quoted 5 lines

arch/x86/video/video-common.c +2 -0

+
+    return false;
   }
   EXPORT_SYMBOL(video_is_primary_device);

In particular, I have hardware that has this exact configuration where two GPUs are marked as primary and have a 'boot_display' attribute: the first one through vga_default_device(), the second one through the new detection method.

Quoted 5 lines

Is this intended?

Kind regards
Aaron

I wouldn't have expected a case like this and I think it means there is a logic error.

Can you please file a kernel bugzilla with details about your system and CC me?

dmesg and lspci -vvnn please

Also; please clarify which GPU shows something when booting up.

Hi

Am 28.10.25 um 14:15 schrieb Mario Limonciello:

Quoted 52 lines · Aaron Erhardt

Quoted 51 lines · Mario Limonciello (AMD)

Quoted 5 lines

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.

I have a question regarding this change. To me, the function name video_is_primary_device() implies that there is only one primary GPU. I would also expect that the 'boot_display' attribute added later in the patch series based on this function is only set for one GPU, but that is not necessarily the case. Since I'm working on a user-space program that reads the 'boot_display' attribute, I need to know what behavior is intended in order to do a correct implementation.

Quoted 35 lines

Reviewed-by Thomas Zimmermann <[email protected]>

Suggested-by Thomas Zimmermann <[email protected]>

Suggested-by Bjorn Helgaas <[email protected]>

Signed-off-by Mario Limonciello (AMD) <[email protected]>

---
v10:
  * Rebase on 6.17-rc1
  * Squash 'fbcon: Stop using screen_info_pci_dev()'
---
  arch/x86/video/video-common.c | 25 ++++++++++++++++++++++++-

  1 file changed, 24 insertions(+), 1 deletion(-)

arch/x86/video/video-common.c +6 -0

index 81fc97a2a837a..e0aeee99bc99e 100644
@@ -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 +28,11 @@ EXPORT_SYMBOL(pgprot_framebuffer);
     bool video_is_primary_device(struct device *dev)
   {
+#ifdef CONFIG_SCREEN_INFO
+    struct screen_info *si = &screen_info;
+    struct resource res[SCREEN_INFO_MAX_RESOURCES];
+    ssize_t i, numres;
+#endif
       struct pci_dev *pdev;
         if (!dev_is_pci(dev))

@@ -34,7 +40,24 @@ bool video_is_primary_device(struct device *dev)
         pdev = to_pci_dev(dev);

Quoted 8 lines

Quoted 8 lines

arch/x86/video/video-common.c bool video_is_primary_device(struct device *dev) · line 47

Quoted 6 lines

arch/x86/video/video-common.c +5 -0

   -    return (pdev == vga_default_device());
+    if (!pci_is_display(pdev))
+        return false;
+
+    if (pdev == vga_default_device())
+        return true;

This can mark a VGA device as primary GPU.

Is the value returned from vga_default_device() eq to NULL?

Quoted 14 lines

Quoted 14 lines

arch/x86/video/video-common.c bool video_is_primary_device(struct device *dev) · line 58

Quoted 12 lines

arch/x86/video/video-common.c +11 -0

+
+#ifdef CONFIG_SCREEN_INFO
+    numres = screen_info_resources(si, res, ARRAY_SIZE(res));
+    for (i = 0; i < numres; ++i) {
+        if (!(res[i].flags & IORESOURCE_MEM))
+            continue;
+
+        if (pci_find_resource(pdev, &res[i]))
+            return true;
+    }
+#endif

And then the new code can also choose a primary GPU.

Maybe we should drop this block or move it to [1]? At [1] it would only run if the more sophisticated vgaarb has been disabled.

The vgaarb now selects CONFIG_SCREEN_INFO and already tests for overlapping resources. There's nothing here that vgaarb shouldn't already do. Yet, I don't understand how only one of the can be true at a time.

[1] https://elixir.bootlin.com/linux/v6.18-rc3/source/include/linux/ vgaarb.h#L55

Quoted 18 lines

Quoted 12 lines

arch/x86/video/video-common.c bool video_is_primary_device(struct device *dev) · line 62

Quoted 6 lines

arch/x86/video/video-common.c +2 -0

+
+    return false;
   }
   EXPORT_SYMBOL(video_is_primary_device);

In particular, I have hardware that has this exact configuration where two GPUs are marked as primary and have a 'boot_display' attribute: the first one through vga_default_device(), the second one through the new detection method.

Quoted 5 lines

Is this intended?

Kind regards
Aaron

Quoted 7 lines

I wouldn't have expected a case like this and I think it means there is a logic error.

Can you please file a kernel bugzilla with details about your system and CC me?

dmesg and lspci -vvnn please

Also; please clarify which GPU shows something when booting up.

Agreed.

Best regards
Thomas

On systems with multiple GPUs there can be uncertainty which GPU is the primary one used to drive the display at bootup. In some desktop environments this can lead to increased power consumption because secondary GPUs may be used for rendering and never go to a low power state. In order to disambiguate this add a new sysfs attribute 'boot_display' that uses the output of video_is_primary_device() to populate whether the PCI device was used for driving the display.

Suggested-by Manivannan Sadhasivam <[email protected]>

Acked-by Manivannan Sadhasivam <[email protected]>

Link https://gitlab.freedesktop.org/xorg/lib/libpciaccess/-/issues/23

Signed-off-by Mario Limonciello (AMD) <[email protected]>

---
v10:
* Rebase on 6.17-rc1
* Drop Thomas' tag, as this is now in a totally different subsystem (although same code)
* Squash "Adjust visibility of boot_display attribute instead of creation"
* Squash "PCI: Move boot display attribute to DRM"

---
  Documentation/ABI/testing/sysfs-class-drm |  8 +++++
  drivers/gpu/drm/drm_sysfs.c               | 41 +++++++++++++++++++++++
  2 files changed, 49 insertions(+)

create mode 100644 Documentation/ABI/testing/sysfs-class-drm

Documentation/ABI/testing/sysfs-class-drm new file +8 -0

new file mode 100644
index 0000000000000..d23fed5e29a74
@@ -0,0 +1,8 @@
+What:		/sys/class/drm/.../boot_display
+Date:		January 2026
+Contact:	Linux DRI developers <[email protected]>
+Description:
+		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".

drivers/gpu/drm/drm_sysfs.c +41 -0

index a455c56dbbeb7..b01ffa4d65098 100644
@@ -18,6 +18,7 @@
  #include <linux/gfp.h>
  #include <linux/i2c.h>
  #include <linux/kdev_t.h>
+#include <linux/pci.h>
  #include <linux/property.h>
  #include <linux/slab.h>
 

@@ -30,6 +31,8 @@
  #include <drm/drm_property.h>
  #include <drm/drm_sysfs.h>
 
+#include <asm/video.h>
+
  #include "drm_internal.h"
  #include "drm_crtc_internal.h"
 

@@ -508,6 +511,43 @@ void drm_sysfs_connector_property_event(struct drm_connector *connector,
  }
  EXPORT_SYMBOL(drm_sysfs_connector_property_event);
 
+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 struct attribute *display_attrs[] = {
+	&dev_attr_boot_display.attr,
+	NULL
+};
+
+static umode_t boot_display_visible(struct kobject *kobj,
+				    struct attribute *a, int n)
+{
+	struct device *dev = kobj_to_dev(kobj)->parent;
+
+	if (dev_is_pci(dev)) {
+		struct pci_dev *pdev = to_pci_dev(dev);
+
+		if (video_is_primary_device(&pdev->dev))
+			return a->mode;
+	}
+
+	return 0;
+}
+
+static const struct attribute_group display_attr_group = {
+	.attrs = display_attrs,
+	.is_visible = boot_display_visible,
+};
+
+static const struct attribute_group *card_dev_groups[] = {
+	&display_attr_group,
+	NULL
+};
+
  struct device *drm_sysfs_minor_alloc(struct drm_minor *minor)
  {
  	const char *minor_str;

@@ -531,6 +571,7 @@ struct device *drm_sysfs_minor_alloc(struct drm_minor *minor)
 
  		kdev->devt = MKDEV(DRM_MAJOR, minor->index);
  		kdev->class = drm_class;
+		kdev->groups = card_dev_groups;
  		kdev->type = &drm_sysfs_device_minor;
  	}
 

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.

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 and avoid changes to userspace. 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).

As the dependendent symbols are in 6.17-rc1 this can merge through drm-misc-next.

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

---
v10:
* Add patches that didn't merge to v6.17-rc1 in
* Move sysfs file to drm ownership

Mario Limonciello (AMD) (4):
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
DRM: Add a new 'boot_display' attribute

  Documentation/ABI/testing/sysfs-class-drm |  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             | 25 +++++++++++++-
  drivers/gpu/drm/drm_sysfs.c               | 41 +++++++++++++++++++++++
  drivers/pci/vgaarb.c                      | 31 +++--------------
  7 files changed, 83 insertions(+), 28 deletions(-)

create mode 100644 Documentation/ABI/testing/sysfs-class-drm

base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585

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.

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 and avoid changes to userspace. 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).

As the dependendent symbols are in 6.17-rc1 this can merge through drm-misc-next.

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

---
v10:
* Add patches that didn't merge to v6.17-rc1 in
* Move sysfs file to drm ownership

Mario Limonciello (AMD) (4):
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
DRM: Add a new 'boot_display' attribute

  Documentation/ABI/testing/sysfs-class-drm |  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             | 25 +++++++++++++-
  drivers/gpu/drm/drm_sysfs.c               | 41 +++++++++++++++++++++++
  drivers/pci/vgaarb.c                      | 31 +++--------------
  7 files changed, 83 insertions(+), 28 deletions(-)

create mode 100644 Documentation/ABI/testing/sysfs-class-drm

base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585