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

Mario Limonciello posted 7 patches 3 months, 3 weeks ago
There is a newer version of this series
[PATCH v3 7/7] fbcon: Make a symlink to the device selected as primary
Posted by Mario Limonciello 3 months, 3 weeks ago 
From: Mario Limonciello <mario.limonciello@amd.com>

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@amd.com>
---
 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
@@ -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)
-- 
2.43.0
Re: [PATCH v3 7/7] fbcon: Make a symlink to the device selected as primary
Posted by Thomas Zimmermann 3 months, 2 weeks ago 
Hi

Am 20.06.25 um 04:49 schrieb Mario Limonciello:
> From: Mario Limonciello <mario.limonciello@amd.com>
>
> 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@amd.com>
> ---
>   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.

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)
Re: [PATCH v3 7/7] fbcon: Make a symlink to the device selected as primary
Posted by Mario Limonciello 3 months, 2 weeks ago 
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@amd.com>
>>
>> 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@amd.com>
>> ---
>>   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)
>
Re: [PATCH v3 7/7] fbcon: Make a symlink to the device selected as primary
Posted by Thomas Zimmermann 3 months, 2 weeks ago 
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@amd.com>
>>>
>>> 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@amd.com>
>>> ---
>>>   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)

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