Deprecate using hints.acpi.0.rsdp to communicate the RSDP to the

system. This uses the hints mechnanism. This mostly works today
because when there's no static hints (the default), this value can be
fetched from the hint. When there is a static hints file, the hint
passed from the boot loader to the kernel is ignored, but for the BIOS
case we're able to find it anyway. However, with UEFI, the fallback
doesn't work, so we get a panic instead.

Switch to acpi.rsdp and use TUNABLE_ULONG_FETCH instead. Continue to
generate the old values to allow for transitions. In addition, fall
back to the old method if the new method isn't present.

Add comments about all this.

Differential Revision: https://reviews.freebsd.org/D5866

1 files changed, 11 insertions, 0 deletions

diff --git a/sys/x86/acpica/OsdEnvironment.c b/sys/x86/acpica/OsdEnvironment.c
index be612b5..ab8a7fb 100644
--- a/sys/x86/acpica/OsdEnvironment.c
+++ b/sys/x86/acpica/OsdEnvironment.c
@@ -30,6 +30,7 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/types.h>
 #include <sys/bus.h>
+#include <sys/kernel.h>
 #include <sys/sysctl.h>
 
 #include <contrib/dev/acpica/include/acpi.h>
@@ -59,6 +60,16 @@ acpi_get_root_from_loader(void)
 {
 	long acpi_root;
 
+	if (TUNABLE_ULONG_FETCH("acpi.rsdp", &acpi_root))
+		return (acpi_root);
+
+	/*
+	 * The hints mechanism is unreliable (it fails if anybody ever
+	 * compiled in hints to the kernel). It has been replaced
+	 * by the tunable method, but is used here as a fallback to
+	 * retain maximum compatibility between old loaders and new
+	 * kernels. It can be removed after 11.0R.
+	 */
 	if (resource_long_value("acpi", 0, "rsdp", &acpi_root) == 0)
 		return (acpi_root);