Re: [PATCH v3 7/7] fbcon: Make a symlink to the device selected as primary

[Mario Limonciello]

On 6/20/25 3:47 AM, Thomas Zimmermann wrote:
> Hi
>
> Am 20.06.25 um 04:49 schrieb Mario Limonciello:
> > From: Mario Limonciello <mario.limonciello@xxxxxxx>
> >
> > Knowing which device is the primary device can be useful for userspace
> > to make decisions on which device to start a display server.
> >
> > Create a link to that device called 'primary_device'.
> >
> > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > ---
> >   drivers/video/fbdev/core/fbcon.c | 10 +++++++++-
> >   1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/ 
> > core/fbcon.c
> > index 2df48037688d1..46f21570723e5 100644
> > --- a/drivers/video/fbdev/core/fbcon.c
> > +++ b/drivers/video/fbdev/core/fbcon.c
>
> You cannot rely on this, as fbcon might be disabled entirely.

So the other idea I had was to have a new file boot_console.

How would you feel about this instead (or even in addition to the symlink)?

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 268c69daa4d5..8535950b4c0f 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_console_show(struct device *dev, struct 
device_attribute *attr,
+                                char *buf)
+{
+       return sysfs_emit(buf, "%u\n", video_is_primary_device(dev));
+}
+static DEVICE_ATTR_RO(boot_console);
+
 static ssize_t boot_vga_show(struct device *dev, struct 
device_attribute *attr,
                             char *buf)
 {
@@ -1698,6 +1706,7 @@ late_initcall(pci_sysfs_init);

 static struct attribute *pci_dev_dev_attrs[] = {
        &dev_attr_boot_vga.attr,
+       &dev_attr_boot_console.attr,
        NULL,
 };

@@ -1710,6 +1719,9 @@ static umode_t pci_dev_attrs_are_visible(struct 
kobject *kobj,
        if (a == &dev_attr_boot_vga.attr && pci_is_vga(pdev))
                return a->mode;

+       if (a == &dev_attr_boot_console.attr && pci_is_display(pdev))
+               return a->mode;
+
        return 0;
 }


> Best regards
> Thomas
>
> > @@ -2934,7 +2934,7 @@ static void fbcon_select_primary(struct fb_info 
> > *info)
> >   {
> >       if (!map_override && primary_device == -1 &&
> >           video_is_primary_device(info->device)) {
> > -        int i;
> > +        int i, r;
> >           printk(KERN_INFO "fbcon: %s (fb%i) is primary device\n",
> >                  info->fix.id, info->node);
> > @@ -2949,6 +2949,10 @@ static void fbcon_select_primary(struct fb_info 
> > *info)
> >                      first_fb_vc + 1, last_fb_vc + 1);
> >               info_idx = primary_device;
> >           }
> > +        r = sysfs_create_link(&fbcon_device->kobj, &info->device->kobj,
> > +                      "primary_device");
> > +        if (r)
> > +            pr_err("fbcon: Failed to link to primary device: %d\n", r);
> >       }
> >   }
> > @@ -3376,6 +3380,10 @@ void __init fb_console_init(void)
> >   void __exit fb_console_exit(void)
> >   {
> > +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DETECT_PRIMARY
> > +    if (primary_device != -1)
> > +        sysfs_remove_link(&fbcon_device->kobj, "primary_device");
> > +#endif
> >   #ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
> >       console_lock();
> >       if (deferred_takeover)