acpi/arm64: ignore 5.1 FADTs that are reported as 5.0

Some Qualcomm Snapdragon based laptops built to run Microsoft Windows
are clearly ACPI 5.1 based, given that that is the first ACPI revision
that supports ARM, and introduced the FADT 'arm_boot_flags' field,
which has a non-zero field on those systems.

So in these cases, infer from the ARM boot flags that the FADT must be
5.1 or later, and treat it as 5.1.

Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Tested-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Graeme Gregory <graeme.gregory@linaro.org>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index 803f0494dd3e3b63f15678ca4700258c2e14cb61..7722e85fb69c30207e57b3183c187c7e9edfdf6e 100644 (file)
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c
@@ -155,10 +155,14 @@ static int __init acpi_fadt_sanity_check(void)
         */
        if (table->revision < 5 ||
           (table->revision == 5 && fadt->minor_revision < 1)) {
-               pr_err("Unsupported FADT revision %d.%d, should be 5.1+\n",
+               pr_err(FW_BUG "Unsupported FADT revision %d.%d, should be 5.1+\n",
                       table->revision, fadt->minor_revision);
-               ret = -EINVAL;
-               goto out;
+
+               if (!fadt->arm_boot_flags) {
+                       ret = -EINVAL;
+                       goto out;
+               }
+               pr_err("FADT has ARM boot flags set, assuming 5.1\n");
        }
 
        if (!(fadt->flags & ACPI_FADT_HW_REDUCED)) {