[RFC 2/6] x86: provide platform-devices for boot-framebuffers

[David Herrmann <dh.herrmann@gmail.com>]

The current situation regarding boot-framebuffers (VGA, VESA/VBE, EFI) on
x86 causes troubles when loading multiple fbdev drivers. The global
"struct screen_info" does not provide any state-tracking about which
drivers use the FBs. request_mem_region() theoretically works, but
unfortunately vesafb/efifb ignore it due to quirks for broken boards.

Avoid this by creating a "platform-framebuffer" device with a pointer
to the "struct screen_info" as platform-data. Drivers can now create
platform-drivers and the driver-core will refuse multiple drivers being
active simultaneously.

We keep the screen_info available for backwards-compatibility. Drivers
can be converted in follow-up patches.

Apart from "platform-framebuffer" devices, this also introduces a
compatibility option for "simple-framebuffer" drivers which recently got
introduced for OF based systems. If CONFIG_X86_SYSFB is selected, we
try to match the screen_info against a simple-framebuffer supported
format. If we succeed, we create a "simple-framebuffer" device instead
of a platform-framebuffer.
This allows to reuse the simplefb.c driver across architectures and also
to introduce a SimpleDRM driver. There is no need to have vesafb.c,
efifb.c, simplefb.c and more just to have architecture specific quirks
in their setup-routines.

Instead, we now move the architecture specific quirks into x86-setup and
provide a generic simple-framebuffer. For backwards-compatibility (if
strange formats are used), we still allow vesafb/efifb to be loaded
simultaneously and pick up all remaining devices.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
---
 arch/x86/Kconfig         |  18 ++++++
 arch/x86/kernel/Makefile |   1 +
 arch/x86/kernel/sysfb.c  | 157 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 176 insertions(+)
 create mode 100644 arch/x86/kernel/sysfb.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index fe120da..8eb06b5 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2255,6 +2255,24 @@ config RAPIDIO
 
 source "drivers/rapidio/Kconfig"
 
+config X86_SYSFB
+	bool "Mark VGA/VBE/EFI FB as generic system framebuffer"
+	help
+	  Firmwares often provide initial graphics framebuffers so the BIOS,
+	  bootloader or kernel can show basic video-output during boot for
+	  user-guidance and debugging. Historically, x86 used the VESA BIOS
+	  Extensions and EFI-framebuffers for this, which are mostly limited
+	  to x86. However, a generic system-framebuffer initialization emerged
+	  recently on some non-x86 architectures.
+	  This option, if enabled, marks VGA/VBE/EFI framebuffers as generic
+	  framebuffers so the new generic system-framebuffer drivers can be
+	  used on x86.
+
+	  This breaks any x86-only driver like efifb, vesafb, uvesafb, which
+	  will not work if this is selected.
+
+	  If unsure, say N.
+
 endmenu
 
 
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 7bd3bd3..1e1005a 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -100,6 +100,7 @@ obj-$(CONFIG_X86_CHECK_BIOS_CORRUPTION) += check.o
 obj-$(CONFIG_SWIOTLB)			+= pci-swiotlb.o
 obj-$(CONFIG_OF)			+= devicetree.o
 obj-$(CONFIG_UPROBES)			+= uprobes.o
+obj-y					+= sysfb.o
 
 obj-$(CONFIG_PERF_EVENTS)		+= perf_regs.o
 
diff --git a/arch/x86/kernel/sysfb.c b/arch/x86/kernel/sysfb.c
new file mode 100644
index 0000000..8272958
--- /dev/null
+++ b/arch/x86/kernel/sysfb.c
@@ -0,0 +1,157 @@
+/*
+ * Generic System Framebuffers on x86
+ * Copyright (c) 2012-2013 David Herrmann <dh.herrmann@gmail.com>
+ */
+
+/*
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ */
+
+/*
+ * Simple-Framebuffer support for x86 systems
+ * Create a platform-device for any available boot framebuffer. The
+ * simple-framebuffer platform device is already available on DT systems, so
+ * this module parses the global "screen_info" object and creates a suitable
+ * platform device compatible with the "simple-framebuffer" DT object. If
+ * the framebuffer is incompatible, we instead create a "platform-framebuffer"
+ * device and pass the screen_info as platform_data. This allows legacy drivers
+ * to pick these devices up without messing with simple-framebuffer drivers.
+ *
+ * If CONFIG_X86_SYSFB is not selected, we never register "simple-framebuffer"
+ * platform devices, but only use "platform-framebuffer" devices for
+ * backwards compatibility.
+ *
+ * TODO: We set the dev_id field of all platform-devices to 0. This allows
+ * other x86 OF/DT parsers to create such devices, too. However, they must
+ * start at offset 1 for this to work.
+ */
+
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/platform_data/simplefb.h>
+#include <linux/platform_device.h>
+#include <linux/screen_info.h>
+
+#ifdef CONFIG_X86_SYSFB
+
+static const char simplefb_resname[] = "BOOTFB";
+
+static const struct simplefb_format formats[] = {
+	SIMPLEFB_FORMATS
+};
+
+static bool parse_mode(const struct screen_info *si,
+		       struct simplefb_platform_data *mode)
+{
+	const struct simplefb_format *f;
+	__u8 type;
+	unsigned int i;
+
+	/* TODO: apply quirks from efifb.c here before probing the devices */
+
+	type = si->orig_video_isVGA;
+	if (type != VIDEO_TYPE_VLFB && type != VIDEO_TYPE_EFI)
+		return false;
+
+	for (i = 0; i < ARRAY_SIZE(formats); ++i) {
+		f = &formats[i];
+		if (si->lfb_depth = f->bits_per_pixel &&
+		    si->red_size = f->red.length &&
+		    si->red_pos = f->red.offset &&
+		    si->green_size = f->green.length &&
+		    si->green_pos = f->green.offset &&
+		    si->blue_size = f->blue.length &&
+		    si->blue_pos = f->blue.offset &&
+		    si->rsvd_size = f->transp.length &&
+		    si->rsvd_pos = f->transp.offset) {
+			strlcpy(mode->format, f->name, sizeof(mode->format));
+			mode->width = si->lfb_width;
+			mode->height = si->lfb_height;
+			mode->stride = si->lfb_linelength;
+			return true;
+		}
+	}
+
+	return false;
+}
+
+static int create_simplefb(const struct screen_info *si,
+			   const struct simplefb_platform_data *mode)
+{
+	struct platform_device *pd;
+	struct resource memres;
+	unsigned long len;
+
+	/* don't use lfb_size as it may contain the whole VMEM instead of only
+	 * the part that is occupied by the framebuffer */
+	len = mode->height * mode->stride;
+	len = PAGE_ALIGN(len);
+	if (len > si->lfb_size << 16) {
+		printk(KERN_WARNING "sysfb: VRAM smaller than advertised\n");
+		return -EINVAL;
+	}
+
+	/* setup IORESOURCE_MEM as framebuffer memory */
+	memset(&memres, 0, sizeof(memres));
+	memres.flags = IORESOURCE_MEM;
+	memres.name = simplefb_resname;
+	memres.start = si->lfb_base;
+	memres.end = si->lfb_base + len - 1;
+	if (memres.end <= memres.start)
+		return -EINVAL;
+
+	pd = platform_device_register_resndata(NULL,
+					       "simple-framebuffer", 0,
+					       &memres, 1,
+					       mode, sizeof(*mode));
+	if (IS_ERR(pd))
+		return PTR_ERR(pd);
+
+	return 0;
+}
+
+#else /* CONFIG_X86_SYSFB */
+
+static bool parse_mode(const struct screen_info *si,
+		       struct simplefb_platform_data *mode)
+{
+	return false;
+}
+
+static int create_simplefb(const struct screen_info *si,
+			   const struct simplefb_platform_data *mode)
+{
+	return -EINVAL;
+}
+
+#endif /* CONFIG_X86_SYSFB */
+
+static __init int add_sysfb(void)
+{
+	const struct screen_info *si = &screen_info;
+	struct simplefb_platform_data mode;
+	struct platform_device *pd;
+	bool compatible = false;
+	int ret;
+
+	compatible = parse_mode(si, &mode);
+
+	ret = -ENODEV;
+	if (compatible)
+		ret = create_simplefb(si, &mode);
+
+	if (ret) {
+		pd = platform_device_register_resndata(NULL,
+						"platform-framebuffer", 0,
+						NULL, 0, si, sizeof(*si));
+		ret = IS_ERR(pd) ? PTR_ERR(pd) : 0;
+	}
+
+	return ret;
+}
+device_initcall(add_sysfb);
-- 
1.8.3.1