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>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b600df82669db000304571fd23c3af90df36190d..68d8acc38c8237e3a77bafc9cfe67528b14778f4 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -12,7 +12,7 @@
        acpi=           [HW,ACPI,X86,ARM64,RISCV64,EARLY]
                        Advanced Configuration and Power Interface
                        Format: { force | on | off | strict | noirq | rsdt |
-                                 copy_dsdt }
+                                 copy_dsdt | nospcr }
                        force -- enable ACPI if default was off
                        on -- enable ACPI but allow fallback to DT [arm64,riscv64]
                        off -- disable ACPI if default was on
@@ -21,8 +21,12 @@
                                strictly ACPI specification compliant.
                        rsdt -- prefer RSDT over (default) XSDT
                        copy_dsdt -- copy DSDT to memory
-                       For ARM64 and RISCV64, ONLY "acpi=off", "acpi=on" or
-                       "acpi=force" are available
+                       nospcr -- disable console in ACPI SPCR table as
+                               default _serial_ console on ARM64
+                       For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or
+                       "acpi=nospcr" are available
+                       For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force"
+                       are available
 
                        See also Documentation/power/runtime_pm.rst, pci=noacpi
 

diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index fd1917336d3ab857d0ed9c751abbc2298467f33d..a73b87ac815c61fcf185c0061c54c72140df8466 100644 (file)
--- 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);
        }