drm: Move nomodeset kernel parameter to drivers/video

Move the nomodeset kernel parameter to drivers/video to make it
available to non-DRM drivers. Adapt the interface, but keep the DRM
interface drm_firmware_drivers_only() to avoid churn within DRM. The
function should later be inlined into callers.

The parameter disables any DRM graphics driver that would replace a
driver for firmware-provided scanout buffers. It is an option to easily
fallback to basic graphics output if the hardware's native driver is
broken. Moving it to a more prominent location wil make it available
to fbdev as well.

v2:
	* clarify the meaning of the nomodeset parameter (Javier)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221111133024.9897-2-tzimmermann@suse.de

1 files changed, 26 insertions, 0 deletions

diff --git a/drivers/video/nomodeset.c b/drivers/video/nomodeset.c
new file mode 100644
index 000000000000..13cc8b719697
--- /dev/null
+++ b/drivers/video/nomodeset.c
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/module.h>
+#include <linux/types.h>
+
+#include <video/nomodeset.h>
+
+static bool video_nomodeset;
+
+bool video_firmware_drivers_only(void)
+{
+	return video_nomodeset;
+}
+EXPORT_SYMBOL(video_firmware_drivers_only);
+
+static int __init disable_modeset(char *str)
+{
+	video_nomodeset = true;
+
+	pr_warn("Booted with the nomodeset parameter. Only the system framebuffer will be available\n");
+
+	return 1;
+}
+
+/* Disable kernel modesetting */
+__setup("nomodeset", disable_modeset);