x86, drivers/pnpbios: Replace paravirt_enabled() check with legacy device check

Since we are removing paravirt_enabled() replace it with a
logical equivalent. Even though PNPBIOS is x86 specific we
add an arch-specific type call, which can be implemented by
any architecture to show how other legacy attribute devices
can later be also checked for with other ACPI legacy attribute
flags.

This implicates the first ACPI 5.2.9.3 IA-PC Boot Architecture
ACPI_FADT_LEGACY_DEVICES flag device, and shows how to add more.

The reason pnpbios gets a defined structure and as such uses
a different approach than the RTC legacy quirk is that ACPI
has a respective RTC flag, while pnpbios does not. We fold
the pnpbios quirk under ACPI_FADT_LEGACY_DEVICES ACPI flag
use case, and use a struct of possible devices to enable
future extensions of this.

As per 0-day, this bumps the vmlinux size using i386-tinyconfig as
follows:

TOTAL TEXT init.text x86_early_init_platform_quirks()
+32 +28 +28 +28

That's 4 byte overhead total, the rest is cleared out on init
as its all __init text.

v2: split out subarch handlng on switch to make it easier
later to add other subarchs. The 'fall-through' switch
handling can be confusing and we'll remove it later
when we add handling for X86_SUBARCH_CE4100.
v3: document vmlinux size impact as per 0-day, and also
explain why pnpbios is treated differently than the
RTC legacy feature.

Signed-off-by: Luis R. Rodriguez <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Brian Gerst <[e-mail]>
Cc: Denys Vlasenko <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
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Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/include/asm/x86_init.h

···
 struct timespec;
 
 /**
+ * struct x86_legacy_devices - legacy x86 devices
+ *
+ * @pnpbios: this platform can have a PNPBIOS. If this is disabled the platform
+ * 	is known to never have a PNPBIOS.
+ *
+ * These are devices known to require LPC or ISA bus. The definition of legacy
+ * devices adheres to the ACPI 5.2.9.3 IA-PC Boot Architecture flag
+ * ACPI_FADT_LEGACY_DEVICES. These devices consist of user visible devices on
+ * the LPC or ISA bus. User visible devices are devices that have end-user
+ * accessible connectors (for example, LPT parallel port). Legacy devices on
+ * the LPC bus consist for example of serial and parallel ports, PS/2 keyboard
+ * / mouse, and the floppy disk controller. A system that lacks all known
+ * legacy devices can assume all devices can be detected exclusively via
+ * standard device enumeration mechanisms including the ACPI namespace.
+ *
+ * A system which has does not have ACPI_FADT_LEGACY_DEVICES enabled must not
+ * have any of the legacy devices enumerated below present.
+ */
+struct x86_legacy_devices {
+	int pnpbios;
+};
+
+/**
  * struct x86_legacy_features - legacy x86 features
  *
  * @rtc: this device has a CMOS real-time clock present
  * @ebda_search: it's safe to search for the EBDA signature in the hardware's
  * 	low RAM
+ * @devices: legacy x86 devices, refer to struct x86_legacy_devices
+ * 	documentation for further details.
  */
 struct x86_legacy_features {
 	int rtc;
 	int ebda_search;
+	struct x86_legacy_devices devices;
 };
 
 /**

arch/x86/kernel/platform-quirks.c

···
 {
 	x86_platform.legacy.rtc = 1;
 	x86_platform.legacy.ebda_search = 0;
+	x86_platform.legacy.devices.pnpbios = 1;
 
 	switch (boot_params.hdr.hardware_subarch) {
 	case X86_SUBARCH_PC:
···
 		break;
 	case X86_SUBARCH_XEN:
 	case X86_SUBARCH_LGUEST:
+		x86_platform.legacy.devices.pnpbios = 0;
+		x86_platform.legacy.rtc = 0;
+		break;
 	case X86_SUBARCH_INTEL_MID:
 		x86_platform.legacy.rtc = 0;
 		break;
···
 	if (x86_platform.set_legacy_features)
 		x86_platform.set_legacy_features();
 }
+
+#if defined(CONFIG_PNPBIOS)
+bool __init arch_pnpbios_disabled(void)
+{
+	return x86_platform.legacy.devices.pnpbios == 0;
+}
+#endif

drivers/pnp/pnpbios/core.c

···
 	int ret;
 
 	if (pnpbios_disabled || dmi_check_system(pnpbios_dmi_table) ||
-	    paravirt_enabled()) {
+	    arch_pnpbios_disabled()) {
 		printk(KERN_INFO "PnPBIOS: Disabled\n");
 		return -ENODEV;
 	}
+
 #ifdef CONFIG_PNPACPI
 	if (!acpi_disabled && !pnpacpi_disabled) {
 		pnpbios_disabled = 1;

include/linux/pnp.h

···
 
 #ifdef CONFIG_PNPBIOS
 extern struct pnp_protocol pnpbios_protocol;
+extern bool arch_pnpbios_disabled(void);
 #define pnp_device_is_pnpbios(dev) ((dev)->protocol == (&pnpbios_protocol))
 #else
 #define pnp_device_is_pnpbios(dev) 0
+#define arch_pnpbios_disabled()	false
 #endif
 
 #ifdef CONFIG_PNPACPI