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

On 06/28/2013 04:11 AM, David Herrmann wrote:

Hi

On Wed, Jun 26, 2013 at 10:49 PM, Stephen Warren [off-list ref] wrote:

quoted

On 06/24/2013 04:27 PM, David Herrmann wrote:

quoted

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.

...

quoted

quoted

diff --git a/arch/x86/kernel/sysfb.c b/arch/x86/kernel/sysfb.c

...

quoted

quoted

+#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 */

Following on from my ifdef comment above, I believe those versions of
those functions will always cause add_sysfb() to return -ENODEV, so you
may as well provide a static inline for add_sysfb() instead.

No. add_sysfb() is supposed to always succeed. However, if
parse_mode/create_simplefb fail, it creates a "platform-framebuffer"
as fallback. I don't see any way to avoid these ifdefs. Considering
the explanation above, could you elaborate how you think this should
work?

Ah, I wasn't getting the fallback mechanism; that if creating a simplefb
wasn't possible or didn't succeed, a platformfb device would be created
instead.

Perhaps the following might be slightly clearer; there are certainly
fewer nesting levels:

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);
	if (compatible) {
		ret = create_simplefb(si, &mode);
		if (!ret)
			return 0;
	}

	pd = platform_device_register_resndata(NULL,
					"platform-framebuffer", 0,
					NULL, 0, si, sizeof(*si));
	ret = IS_ERR(pd) ? PTR_ERR(pd) : 0;

	return ret;
}