On Mon, Feb 22, 2016 at 04:45:17PM +0100, Matthias Brugger wrote:

On 22/02/16 14:46, Aleksey Makarov wrote:

quoted

From: Leif Lindholm <redacted>

In order to support selecting earlycon via either ACPI or DT, move
the decision on whether to attempt ACPI configuration into the
early_param handling. Then make acpi_boot_table_init() bail out if
acpi_disabled.

Signed-off-by: Leif Lindholm <redacted>
---
 arch/arm64/kernel/acpi.c | 54 ++++++++++++++++++++++++++----------------------
 1 file changed, 29 insertions(+), 25 deletions(-)

diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index d1ce8e2..7a944f7 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c

@@ -44,6 +44,19 @@ EXPORT_SYMBOL(acpi_pci_disabled);
 static bool param_acpi_off __initdata;
 static bool param_acpi_force __initdata;

+static int __init dt_scan_depth1_nodes(unsigned long node,
+				       const char *uname, int depth,
+				       void *data)
+{
+	/*
+	 * Return 1 as soon as we encounter a node at depth 1 that is
+	 * not the /chosen node.
+	 */
+	if (depth == 1 && (strcmp(uname, "chosen") != 0))
+		return 1;
+	return 0;
+}
+
 static int __init parse_acpi(char *arg)
 {
 	if (!arg)

@@ -57,23 +70,27 @@ static int __init parse_acpi(char *arg)
 	else
 		return -EINVAL;	/* Core will print when we return error */

-	return 0;
-}
-early_param("acpi", parse_acpi);
+	/*
+	 * Enable ACPI instead of device tree unless
+	 * - ACPI has been disabled explicitly (acpi=off), or
+	 * - the device tree is not empty (it has more than just a /chosen node)
+	 *   and ACPI has not been force enabled (acpi=force)
+	 */
+	if (param_acpi_off ||
+	    (!param_acpi_force && of_scan_flat_dt(dt_scan_depth1_nodes, NULL)))
+		return 0;

-static int __init dt_scan_depth1_nodes(unsigned long node,
-				       const char *uname, int depth,
-				       void *data)
-{
 	/*
-	 * Return 1 as soon as we encounter a node at depth 1 that is
-	 * not the /chosen node.
+	 * ACPI is disabled at this point. Enable it in order to parse
+	 * the ACPI tables and carry out sanity checks
 	 */
-	if (depth == 1 && (strcmp(uname, "chosen") != 0))
-		return 1;
+	enable_acpi();
+

So we only enable ACPI if we pass acpi=force as kernel parameter?
I'm not sure if this is what you wanted to do.

The current preference from ARM64 maintainers was that is both ACPI
tables and a DT were presented then DT should take precedence.

With no DT provided the code should use ACPI.

Graeme