ACPI: Add acpi=nospcr to disable ACPI SPCR as default console on ARM64

For varying privacy and security reasons, sometimes we would like to
completely silence the _serial_ console, and only enable it when needed.

But there are many existing systems that depend on this _serial_ console,
so add acpi=nospcr to disable console in ACPI SPCR table as default
_serial_ console.

Signed-off-by: Liu Wei <liuwei09@cestc.cn>
Suggested-by: Prarit Bhargava <prarit@redhat.com>
Suggested-by: Will Deacon <will@kernel.org>
Suggested-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Prarit Bhargava <prarit@redhat.com>
Link: https://lore.kernel.org/r/20240625030504.58025-1-liuwei09@cestc.cn
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 17 insertions, 1 deletions

diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index fd1917336d3a..a73b87ac815c 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c
@@ -45,6 +45,7 @@ EXPORT_SYMBOL(acpi_pci_disabled);
 static bool param_acpi_off __initdata;
 static bool param_acpi_on __initdata;
 static bool param_acpi_force __initdata;
+static bool param_acpi_nospcr __initdata;
 
 static int __init parse_acpi(char *arg)
 {
@@ -58,6 +59,8 @@ static int __init parse_acpi(char *arg)
 		param_acpi_on = true;
 	else if (strcmp(arg, "force") == 0) /* force ACPI to be enabled */
 		param_acpi_force = true;
+	else if (strcmp(arg, "nospcr") == 0) /* disable SPCR as default console */
+		param_acpi_nospcr = true;
 	else
 		return -EINVAL;	/* Core will print when we return error */
 
@@ -237,7 +240,20 @@ done:
 			acpi_put_table(facs);
 		}
 #endif
-		acpi_parse_spcr(earlycon_acpi_spcr_enable, true);
+
+		/*
+		 * For varying privacy and security reasons, sometimes need
+		 * to completely silence the serial console output, and only
+		 * enable it when needed.
+		 * But there are many existing systems that depend on this
+		 * behaviour, use acpi=nospcr to disable console in ACPI SPCR
+		 * table as default serial console.
+		 */
+		acpi_parse_spcr(earlycon_acpi_spcr_enable,
+			!param_acpi_nospcr);
+		pr_info("Use ACPI SPCR as default console: %s\n",
+				param_acpi_nospcr ? "No" : "Yes");
+
 		if (IS_ENABLED(CONFIG_ACPI_BGRT))
 			acpi_table_parse(ACPI_SIG_BGRT, acpi_parse_bgrt);
 	}