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

[Thomas Zimmermann]

Hi

Am 20.06.25 um 17:56 schrieb 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.

'console' already has a meaning, so I'd prefer boot_display. Apart from 
naming, this is a good idea.

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

We likely won't need the symlink then.

Best regards
Thomas

> 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)

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)