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

Documentation/admin-guide/kernel-parameters.txt

@@ -3777,12 +3777,15 @@
 			shutdown the other cpus.  Instead use the REBOOT_VECTOR
 			irq.
 
-	nomodeset	Disable kernel modesetting. DRM drivers will not perform
-			display-mode changes or accelerated rendering. Only the
-			system framebuffer will be available for use if this was
-			set-up by the firmware or boot loader.
-
-			Useful as fallback, or for testing and debugging.
+	nomodeset	Disable kernel modesetting. Most systems' firmware
+			sets up a display mode and provides framebuffer memory
+			for output. With nomodeset, DRM and fbdev drivers will
+			not load if they could possibly displace the pre-
+			initialized output. Only the system framebuffer will
+			be available for use. The respective drivers will not
+			perform display-mode changes or accelerated rendering.
+
+			Useful as error fallback, or for testing and debugging.
 
 	nomodule	Disable module load
 

MAINTAINERS

@@ -6701,8 +6701,10 @@ F:	drivers/gpu/drm/drm_aperture.c
 F:	drivers/gpu/drm/tiny/ofdrm.c
 F:	drivers/gpu/drm/tiny/simpledrm.c
 F:	drivers/video/aperture.c
+F:	drivers/video/nomodeset.c
 F:	include/drm/drm_aperture.h
 F:	include/linux/aperture.h
+F:	include/video/nomodeset.h
 
 DRM DRIVER FOR SIS VIDEO CARDS
 S:	Orphan / Obsolete

drivers/gpu/drm/Kconfig

@@ -8,7 +8,6 @@
 menuconfig DRM
 	tristate "Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)"
 	depends on (AGP || AGP=n) && !EMULATED_CMPXCHG && HAS_DMA
-	select DRM_NOMODESET
 	select DRM_PANEL_ORIENTATION_QUIRKS
 	select HDMI
 	select FB_CMDLINE
@@ -19,6 +18,7 @@ menuconfig DRM
 # gallium uses SYS_kcmp for os_same_file_description() to de-duplicate
 # device and dmabuf fd. Let's make sure that is available for our userspace.
 	select KCMP
+	select VIDEO_NOMODESET
 	help
 	  Kernel-level support for the Direct Rendering Infrastructure (DRI)
 	  introduced in XFree86 4.0. If you say Y here, you need to select
@@ -514,11 +514,6 @@ config DRM_EXPORT_FOR_TESTS
 config DRM_PANEL_ORIENTATION_QUIRKS
 	tristate
 
-# Separate option because nomodeset parameter is global and expected built-in
-config DRM_NOMODESET
-	bool
-	default n
-
 config DRM_LIB_RANDOM
 	bool
 	default n

drivers/gpu/drm/Makefile

@@ -72,7 +72,6 @@ drm-$(CONFIG_DRM_PRIVACY_SCREEN) += \
 	drm_privacy_screen_x86.o
 obj-$(CONFIG_DRM)	+= drm.o
 
-obj-$(CONFIG_DRM_NOMODESET) += drm_nomodeset.o
 obj-$(CONFIG_DRM_PANEL_ORIENTATION_QUIRKS) += drm_panel_orientation_quirks.o
 
 #

drivers/video/Kconfig

@@ -11,6 +11,10 @@ config APERTURE_HELPERS
 	  Support tracking and hand-over of aperture ownership. Required
 	  by graphics drivers for firmware-provided framebuffers.
 
+config VIDEO_NOMODESET
+	bool
+	default n
+
 if HAS_IOMEM
 
 config HAVE_FB_ATMEL

drivers/video/Makefile

@@ -2,6 +2,7 @@
 
 obj-$(CONFIG_APERTURE_HELPERS)    += aperture.o
 obj-$(CONFIG_VGASTATE)            += vgastate.o
+obj-$(CONFIG_VIDEO_NOMODESET)     += nomodeset.o
 obj-$(CONFIG_HDMI)                += hdmi.o
 
 obj-$(CONFIG_VT)		  += console/

drivers/gpu/drm/drm_nomodeset.c → drivers/video/nomodeset.c

@@ -3,17 +3,19 @@
 #include <linux/module.h>
 #include <linux/types.h>
 
-static bool drm_nomodeset;
+#include <video/nomodeset.h>
 
-bool drm_firmware_drivers_only(void)
+static bool video_nomodeset;
+
+bool video_firmware_drivers_only(void)
 {
-	return drm_nomodeset;
+	return video_nomodeset;
 }
-EXPORT_SYMBOL(drm_firmware_drivers_only);
+EXPORT_SYMBOL(video_firmware_drivers_only);
 
 static int __init disable_modeset(char *str)
 {
-	drm_nomodeset = true;
+	video_nomodeset = true;
 
 	pr_warn("Booted with the nomodeset parameter. Only the system framebuffer will be available\n");
 

include/drm/drm_drv.h

@@ -30,6 +30,8 @@
 #include <linux/list.h>
 #include <linux/irqreturn.h>
 
+#include <video/nomodeset.h>
+
 #include <drm/drm_device.h>
 
 struct drm_file;
@@ -602,6 +604,10 @@ static inline bool drm_drv_uses_atomic_modeset(struct drm_device *dev)
 
 int drm_dev_set_unique(struct drm_device *dev, const char *name);
 
-extern bool drm_firmware_drivers_only(void);
+/* TODO: Inline drm_firmware_drivers_only() in all its callers. */
+static inline bool drm_firmware_drivers_only(void)
+{
+	return video_firmware_drivers_only();
+}
 
 #endif

include/video/nomodeset.h

+/* SPDX-License-Identifier: MIT */
+
+#ifndef VIDEO_NOMODESET_H
+#define VIDEO_NOMODESET_H
+
+bool video_firmware_drivers_only(void);
+
+#endif