[PATCH] sysfb: Fix screen_info type check for VGA

[PATCH] sysfb: Fix screen_info type check for VGA

[Thomas Zimmermann]

Use the helper screen_info_video_type() to get the framebuffer
type from struct screen_info. Handle supported values in sorted
switch statement.

Reading orig_video_isVGA is unreliable. On most systems it is a
VIDEO_TYPE_ constant. On some systems with VGA it is simply set
to 1 to signal the presence of a VGA output. See vga_probe() for
an example. Retrieving the screen_info type with the helper
screen_info_video_type() detects these cases and returns the
appropriate VIDEO_TYPE_ constant. For VGA, sysfb creates a device
named "vga-framebuffer".

The sysfb code has been taken from vga16fb, where it likely didn't
work correctly either. With this bugfix applied, vga16fb loads for
compatible vga-framebuffer devices.

Fixes: 0db5b61e0dc0 ("fbdev/vga16fb: Create EGA/VGA devices in sysfb code")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Tzung-Bi Shih <tzungbi@kernel.org>
Cc: Helge Deller <deller@gmx.de>
Cc: "Uwe Kleine-König" <u.kleine-koenig@baylibre.com>
Cc: Zsolt Kajtar <soci@c64.rulez.org>
Cc: <stable@vger.kernel.org> # v6.1+
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/firmware/sysfb.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c
index 7c5c03f274b9..889e5b05c739 100644
--- a/drivers/firmware/sysfb.c
+++ b/drivers/firmware/sysfb.c
@@ -143,6 +143,7 @@ static __init int sysfb_init(void)
 {
 	struct screen_info *si = &screen_info;
 	struct device *parent;
+	unsigned int type;
 	struct simplefb_platform_data mode;
 	const char *name;
 	bool compatible;
@@ -170,17 +171,26 @@ static __init int sysfb_init(void)
 			goto put_device;
 	}
 
+	type = screen_info_video_type(si);
+
 	/* if the FB is incompatible, create a legacy framebuffer device */
-	if (si->orig_video_isVGA == VIDEO_TYPE_EFI)
-		name = "efi-framebuffer";
-	else if (si->orig_video_isVGA == VIDEO_TYPE_VLFB)
-		name = "vesa-framebuffer";
-	else if (si->orig_video_isVGA == VIDEO_TYPE_VGAC)
-		name = "vga-framebuffer";
-	else if (si->orig_video_isVGA == VIDEO_TYPE_EGAC)
+	switch (type) {
+	case VIDEO_TYPE_EGAC:
 		name = "ega-framebuffer";
-	else
+		break;
+	case VIDEO_TYPE_VGAC:
+		name = "vga-framebuffer";
+		break;
+	case VIDEO_TYPE_VLFB:
+		name = "vesa-framebuffer";
+		break;
+	case VIDEO_TYPE_EFI:
+		name = "efi-framebuffer";
+		break;
+	default:
 		name = "platform-framebuffer";
+		break;
+	}
 
 	pd = platform_device_alloc(name, 0);
 	if (!pd) {
-- 
2.49.0

Re: [PATCH] sysfb: Fix screen_info type check for VGA

[Tzung-Bi Shih]

On Tue, Jun 03, 2025 at 05:48:20PM +0200, Thomas Zimmermann wrote:
> Use the helper screen_info_video_type() to get the framebuffer
> type from struct screen_info. Handle supported values in sorted
> switch statement.
> 
> Reading orig_video_isVGA is unreliable. On most systems it is a
> VIDEO_TYPE_ constant. On some systems with VGA it is simply set
> to 1 to signal the presence of a VGA output. See vga_probe() for
> an example. Retrieving the screen_info type with the helper
> screen_info_video_type() detects these cases and returns the
> appropriate VIDEO_TYPE_ constant. For VGA, sysfb creates a device
> named "vga-framebuffer".
> 
> The sysfb code has been taken from vga16fb, where it likely didn't
> work correctly either. With this bugfix applied, vga16fb loads for
> compatible vga-framebuffer devices.
> 
> Fixes: 0db5b61e0dc0 ("fbdev/vga16fb: Create EGA/VGA devices in sysfb code")
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Javier Martinez Canillas <javierm@redhat.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Tzung-Bi Shih <tzungbi@kernel.org>
> Cc: Helge Deller <deller@gmx.de>
> Cc: "Uwe Kleine-König" <u.kleine-koenig@baylibre.com>
> Cc: Zsolt Kajtar <soci@c64.rulez.org>
> Cc: <stable@vger.kernel.org> # v6.1+
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>

Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>

Re: [PATCH] sysfb: Fix screen_info type check for VGA

[Javier Martinez Canillas]

Thomas Zimmermann <tzimmermann@suse.de> writes:

> Use the helper screen_info_video_type() to get the framebuffer
> type from struct screen_info. Handle supported values in sorted
> switch statement.
>
> Reading orig_video_isVGA is unreliable. On most systems it is a
> VIDEO_TYPE_ constant. On some systems with VGA it is simply set
> to 1 to signal the presence of a VGA output. See vga_probe() for
> an example. Retrieving the screen_info type with the helper
> screen_info_video_type() detects these cases and returns the
> appropriate VIDEO_TYPE_ constant. For VGA, sysfb creates a device
> named "vga-framebuffer".
>
> The sysfb code has been taken from vga16fb, where it likely didn't
> work correctly either. With this bugfix applied, vga16fb loads for
> compatible vga-framebuffer devices.
>

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat