fbdev: Add support for the nomodeset kernel parameter

Support the kernel's nomodeset parameter for all PCI-based fbdev
drivers that use aperture helpers to remove other, hardware-agnostic
graphics drivers.

The parameter is a simple way of using the firmware-provided scanout
buffer if the hardware's native driver is broken. The same effect
could be achieved with per-driver options, but the importance of the
graphics output for many users makes a single, unified approach
worthwhile.

With nomodeset specified, the fbdev driver module will not load. This
unifies behavior with similar DRM drivers. In DRM helpers, modules
first check the nomodeset parameter before registering the PCI
driver. As fbdev has no such module helpers, we have to modify each
driver individually.

The name 'nomodeset' is slightly misleading, but has been chosen for
historical reasons. Several drivers implemented it before it became a
general option for DRM. So keeping the existing name was preferred over
introducing a new one.

v2:
	* print a warning if a driver does not init (Helge)
	* wrap video_firmware_drivers_only() in helper

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221111133024.9897-3-tzimmermann@suse.de

1 files changed, 9 insertions, 0 deletions

diff --git a/include/linux/fb.h b/include/linux/fb.h
index 731fad5e39fa..8dc9635f5bc1 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -804,6 +804,15 @@ extern int fb_find_mode(struct fb_var_screeninfo *var,
 			const struct fb_videomode *default_mode,
 			unsigned int default_bpp);
 
+#if defined(CONFIG_VIDEO_NOMODESET)
+bool fb_modesetting_disabled(const char *drvname);
+#else
+bool fb_modesetting_disabled(const char *drvname)
+{
+	return false;
+}
+#endif
+
 /* Convenience logging macros */
 #define fb_err(fb_info, fmt, ...)					\
 	pr_err("fb%d: " fmt, (fb_info)->node, ##__VA_ARGS__)