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 <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230209135509.7786-9-tzimmermann@suse.de

1 files changed, 133 insertions, 0 deletions

diff --git a/drivers/video/cmdline.c b/drivers/video/cmdline.c
new file mode 100644
index 000000000000..d3d257489c3d
--- /dev/null
+++ b/drivers/video/cmdline.c
@@ -0,0 +1,133 @@
+// 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 <brad@neruo.com>
+ *
+ * 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 <daniel.vetter@ffwll.ch>
+ */
+
+#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);