video: Add helpers for decoding screen_info

The plain values as stored in struct screen_info need to be decoded
before being used. Add helpers that decode the type of video output
and the framebuffer I/O aperture.

Old or non-x86 systems may not set the type of video directly, but
only indicate the presence by storing 0x01 in orig_video_isVGA. The
decoding logic in screen_info_video_type() takes this into account.
It then follows similar code in vgacon's vgacon_startup() to detect
the video type from the given values.

A call to screen_info_resources() returns all known resources of the
given screen_info. The resources' values have been taken from existing
code in vgacon and vga16fb. These drivers can later be converted to
use the new interfaces.

v2:
	* return ssize_t from screen_info_resources()
	* don't call __screen_info_has_lfb() unnecessarily

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240212090736.11464-2-tzimmermann@suse.de

1 files changed, 100 insertions, 0 deletions

diff --git a/include/linux/screen_info.h b/include/linux/screen_info.h
index eab7081392d5..e7a02c5609d1 100644
--- a/include/linux/screen_info.h
+++ b/include/linux/screen_info.h
@@ -4,6 +4,106 @@
 
 #include <uapi/linux/screen_info.h>
 
+/**
+ * SCREEN_INFO_MAX_RESOURCES - maximum number of resources per screen_info
+ */
+#define SCREEN_INFO_MAX_RESOURCES	3
+
+struct resource;
+
+static inline bool __screen_info_has_lfb(unsigned int type)
+{
+	return (type == VIDEO_TYPE_VLFB) || (type == VIDEO_TYPE_EFI);
+}
+
+static inline u64 __screen_info_lfb_base(const struct screen_info *si)
+{
+	u64 lfb_base = si->lfb_base;
+
+	if (si->capabilities & VIDEO_CAPABILITY_64BIT_BASE)
+		lfb_base |= (u64)si->ext_lfb_base << 32;
+
+	return lfb_base;
+}
+
+static inline u64 __screen_info_lfb_size(const struct screen_info *si, unsigned int type)
+{
+	u64 lfb_size = si->lfb_size;
+
+	if (type == VIDEO_TYPE_VLFB)
+		lfb_size <<= 16;
+	return lfb_size;
+}
+
+static inline unsigned int __screen_info_video_type(unsigned int type)
+{
+	switch (type) {
+	case VIDEO_TYPE_MDA:
+	case VIDEO_TYPE_CGA:
+	case VIDEO_TYPE_EGAM:
+	case VIDEO_TYPE_EGAC:
+	case VIDEO_TYPE_VGAC:
+	case VIDEO_TYPE_VLFB:
+	case VIDEO_TYPE_PICA_S3:
+	case VIDEO_TYPE_MIPS_G364:
+	case VIDEO_TYPE_SGI:
+	case VIDEO_TYPE_TGAC:
+	case VIDEO_TYPE_SUN:
+	case VIDEO_TYPE_SUNPCI:
+	case VIDEO_TYPE_PMAC:
+	case VIDEO_TYPE_EFI:
+		return type;
+	default:
+		return 0;
+	}
+}
+
+/**
+ * screen_info_video_type() - Decodes the video type from struct screen_info
+ * @si: an instance of struct screen_info
+ *
+ * Returns:
+ * A VIDEO_TYPE_ constant representing si's type of video display, or 0 otherwise.
+ */
+static inline unsigned int screen_info_video_type(const struct screen_info *si)
+{
+	unsigned int type;
+
+	// check if display output is on
+	if (!si->orig_video_isVGA)
+		return 0;
+
+	// check for a known VIDEO_TYPE_ constant
+	type = __screen_info_video_type(si->orig_video_isVGA);
+	if (type)
+		return si->orig_video_isVGA;
+
+	// check if text mode has been initialized
+	if (!si->orig_video_lines || !si->orig_video_cols)
+		return 0;
+
+	// 80x25 text, mono
+	if (si->orig_video_mode == 0x07) {
+		if ((si->orig_video_ega_bx & 0xff) != 0x10)
+			return VIDEO_TYPE_EGAM;
+		else
+			return VIDEO_TYPE_MDA;
+	}
+
+	// EGA/VGA, 16 colors
+	if ((si->orig_video_ega_bx & 0xff) != 0x10) {
+		if (si->orig_video_isVGA)
+			return VIDEO_TYPE_VGAC;
+		else
+			return VIDEO_TYPE_EGAC;
+	}
+
+	// the rest...
+	return VIDEO_TYPE_CGA;
+}
+
+ssize_t screen_info_resources(const struct screen_info *si, struct resource *r, size_t num);
+
 extern struct screen_info screen_info;
 
 #endif /* _SCREEN_INFO_H */