fbdev: Handle video= parameter in video/cmdline.c

Handle the command-line parameter video= in video/cmdline.c. Implement
the fbdev helper fb_get_options() on top. Will allows to handle the
kernel parameter in DRM without fbdev dependencies.

Note that __video_get_options() has the meaning of its return value
inverted compared to fb_get_options(). The new helper returns true if
the adapter has been enabled, and false otherwise.

There is the ofonly parameter, which disables output for non-OF-based
framebuffers. It is only for offb and looks like a workaround. The actual
purpose it not clear to me. Use 'video=off' or 'nomodeset' instead.

Signed-off-by: Thomas Zimmermann <[e-mail]>
Reviewed-by: Javier Martinez Canillas <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/Kconfig

···
 	depends on (AGP || AGP=n) && !EMULATED_CMPXCHG && HAS_DMA
 	select DRM_PANEL_ORIENTATION_QUIRKS
 	select HDMI
-	select FB_CMDLINE
 	select I2C
 	select DMA_SHARED_BUFFER
 	select SYNC_FILE
 # 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_CMDLINE
 	select VIDEO_NOMODESET
 	help
 	  Kernel-level support for the Direct Rendering Infrastructure (DRI)

drivers/video/Kconfig

···
 	  Support tracking and hand-over of aperture ownership. Required
 	  by graphics drivers for firmware-provided framebuffers.
 
+config VIDEO_CMDLINE
+	bool
+
 config VIDEO_NOMODESET
 	bool
 	default n

drivers/video/Makefile

···
 
 obj-$(CONFIG_APERTURE_HELPERS)    += aperture.o
 obj-$(CONFIG_VGASTATE)            += vgastate.o
+obj-$(CONFIG_VIDEO_CMDLINE)       += cmdline.o
 obj-$(CONFIG_VIDEO_NOMODESET)     += nomodeset.o
 obj-$(CONFIG_HDMI)                += hdmi.o
 

drivers/video/cmdline.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Based on the fbdev code in drivers/video/fbdev/core/fb_cmdline:
+ *
+ *  Copyright (C) 2014 Intel Corp
+ *  Copyright (C) 1994 Martin Schaller
+ *
+ *	2001 - Documented with DocBook
+ *	- Brad Douglas <[e-mail]>
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of this archive
+ * for more details.
+ *
+ * Authors:
+ *    Daniel Vetter <[e-mail]>
+ */
+
+#include <linux/fb.h> /* for FB_MAX */
+#include <linux/init.h>
+
+#include <video/cmdline.h>
+
+/*
+ * FB_MAX is the maximum number of framebuffer devices and also
+ * the maximum number of video= parameters. Although not directly
+ * related to each other, it makes sense to keep it that way.
+ */
+static const char *video_options[FB_MAX] __read_mostly;
+static const char *video_option __read_mostly;
+static int video_of_only __read_mostly;
+
+static const char *__video_get_option_string(const char *name)
+{
+	const char *options = NULL;
+	size_t name_len = 0;
+
+	if (name)
+		name_len = strlen(name);
+
+	if (name_len) {
+		unsigned int i;
+		const char *opt;
+
+		for (i = 0; i < ARRAY_SIZE(video_options); ++i) {
+			if (!video_options[i])
+				continue;
+			if (video_options[i][0] == '\0')
+				continue;
+			opt = video_options[i];
+			if (!strncmp(opt, name, name_len) && opt[name_len] == ':')
+				options = opt + name_len + 1;
+		}
+	}
+
+	/* No match, return global options */
+	if (!options)
+		options = video_option;
+
+	return options;
+}
+
+/**
+ * video_get_options - get kernel boot parameters
+ * @name:	name of the output as it would appear in the boot parameter
+ *		line (video=<name>:<options>)
+ *
+ * Looks up the video= options for the given name. Names are connector
+ * names with DRM, or driver names with fbdev. If no video option for
+ * the name has been specified, the function returns the global video=
+ * setting. A @name of NULL always returns the global video setting.
+ *
+ * Returns:
+ * The string of video options for the given name, or NULL if no video
+ * option has been specified.
+ */
+const char *video_get_options(const char *name)
+{
+	return __video_get_option_string(name);
+}
+EXPORT_SYMBOL(video_get_options);
+
+bool __video_get_options(const char *name, const char **options, bool is_of)
+{
+	bool enabled = true;
+	const char *opt = NULL;
+
+	if (video_of_only && !is_of)
+		enabled = false;
+
+	opt = __video_get_option_string(name);
+
+	if (options)
+		*options = opt;
+
+	return enabled;
+}
+EXPORT_SYMBOL(__video_get_options);
+
+/*
+ * Process command line options for video adapters. This function is
+ * a __setup and __init function. It only stores the options. Drivers
+ * have to call video_get_options() as necessary.
+ */
+static int __init video_setup(char *options)
+{
+	if (!options || !*options)
+		goto out;
+
+	if (!strncmp(options, "ofonly", 6)) {
+		video_of_only = true;
+		goto out;
+	}
+
+	if (strchr(options, ':')) {
+		/* named */
+		size_t i;
+
+		for (i = 0; i < ARRAY_SIZE(video_options); i++) {
+			if (!video_options[i]) {
+				video_options[i] = options;
+				break;
+			}
+		}
+	} else {
+		/* global */
+		video_option = options;
+	}
+
+out:
+	return 1;
+}
+__setup("video=", video_setup);

drivers/video/fbdev/Kconfig

···
 # fbdev configuration
 #
 
-config FB_CMDLINE
-	bool
-
 config FB_NOTIFY
 	bool
 
 menuconfig FB
 	tristate "Support for frame buffer devices"
-	select FB_CMDLINE
 	select FB_NOTIFY
+	select VIDEO_CMDLINE
 	help
 	  The frame buffer device provides an abstraction for the graphics
 	  hardware. It represents the frame buffer of some video hardware and

drivers/video/fbdev/core/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
-obj-$(CONFIG_FB_CMDLINE)          += fb_cmdline.o
 obj-$(CONFIG_FB_NOTIFY)           += fb_notify.o
 obj-$(CONFIG_FB)                  += fb.o
 fb-y                              := fbmem.o fbmon.o fbcmap.o fbsysfs.o \
-                                     modedb.o fbcvt.o
+                                     modedb.o fbcvt.o fb_cmdline.o
 fb-$(CONFIG_FB_DEFERRED_IO)       += fb_defio.o
 
 ifeq ($(CONFIG_FRAMEBUFFER_CONSOLE),y)

drivers/video/fbdev/core/fb_cmdline.c

···
  * Authors:
  *    Daniel Vetter <[e-mail]>
  */
-#include <linux/init.h>
+
+#include <linux/export.h>
 #include <linux/fb.h>
+#include <linux/string.h>
 
-static char *video_options[FB_MAX] __read_mostly;
-static const char *fb_mode_option __read_mostly;
-static int ofonly __read_mostly;
-
-static const char *__fb_get_options(const char *name)
-{
-	const char *options = NULL;
-	size_t name_len = 0;
-
-	if (name)
-		name_len = strlen(name);
-
-	if (name_len) {
-		unsigned int i;
-		const char *opt;
-
-		for (i = 0; i < ARRAY_SIZE(video_options); ++i) {
-			if (!video_options[i])
-				continue;
-			if (video_options[i][0] == '\0')
-				continue;
-			opt = video_options[i];
-			if (!strncmp(opt, name, name_len) && opt[name_len] == ':')
-				options = opt + name_len + 1;
-		}
-	}
-
-	/* No match, return global options */
-	if (!options)
-		options = fb_mode_option;
-
-	return options;
-}
+#include <video/cmdline.h>
 
 /**
  * fb_get_options - get kernel boot parameters
···
  */
 int fb_get_options(const char *name, char **option)
 {
-	int retval = 0;
-	const char *options;
+	const char *options = NULL;
+	bool is_of = false;
+	bool enabled;
 
-	if (name && ofonly && strncmp(name, "offb", 4))
-		retval = 1;
+	if (name)
+		is_of = strncmp(name, "offb", 4);
 
-	options = __fb_get_options(name);
+	enabled = __video_get_options(name, &options, is_of);
 
 	if (options) {
 		if (!strncmp(options, "off", 3))
-			retval = 1;
+			enabled = false;
 	}
 
 	if (option) {
···
 			*option = NULL;
 	}
 
-	return retval;
+	return enabled ? 0 : 1; // 0 on success, 1 otherwise
 }
 EXPORT_SYMBOL(fb_get_options);
-
-/**
- *	video_setup - process command line options
- *	@options: string of options
- *
- *	Process command line options for frame buffer subsystem.
- *
- *	NOTE: This function is a __setup and __init function.
- *            It only stores the options.  Drivers have to call
- *            fb_get_options() as necessary.
- */
-static int __init video_setup(char *options)
-{
-	if (!options || !*options)
-		goto out;
-
-	if (!strncmp(options, "ofonly", 6)) {
-		ofonly = 1;
-		goto out;
-	}
-
-	if (strchr(options, ':')) {
-		/* named */
-		int i;
-
-		for (i = 0; i < FB_MAX; i++) {
-			if (video_options[i] == NULL) {
-				video_options[i] = options;
-				break;
-			}
-		}
-	} else {
-		/* global */
-		fb_mode_option = options;
-	}
-
-out:
-	return 1;
-}
-__setup("video=", video_setup);

include/video/cmdline.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef VIDEO_CMDLINE_H
+#define VIDEO_CMDLINE_H
+
+#include <linux/types.h>
+
+#if defined(CONFIG_VIDEO_CMDLINE)
+const char *video_get_options(const char *name);
+
+/* exported for compatibility with fbdev; don't use in new code */
+bool __video_get_options(const char *name, const char **option, bool is_of);
+#else
+static inline const char *video_get_options(const char *name)
+{
+	return NULL;
+}
+#endif
+
+#endif