On 2015/3/19 4:07, Ard Biesheuvel wrote:

On 18 March 2015 at 12:35, Lorenzo Pieralisi [off-list ref] wrote:

quoted

On Wed, Mar 11, 2015 at 12:39:34PM +0000, Hanjun Guo wrote:

quoted

From: Al Stone <redacted>

This implements the following policy to decide whether ACPI should
be used to boot the system:
- acpi=off: ACPI will not be used to boot the system, even if there is
  no alternative available (e.g., device tree is empty)
- acpi=force: only ACPI will be used to boot the system; if that fails,
  there will be no fallback to alternative methods (such as device tree)

I think this comment is stale. acpi=force enables ACPI and tries to
init the ACPI tables without even checking DT, but it does fall back to
DT if ACPI table init fails (by disabling ACPI and unflattening the
FDT).

Am I wrong ?

No, you're right. But I would suggest that we fix the code, not the comment.

I agree. If user pass "acpi=force", I think it means ACPI only, so if
ACPI fails, we can just not going to boot the system.

I think we are all in agreement on the policy, we only need to make
disable_acpi() conditional on whether acpi_param_force is set

I prefer Catalin's suggestion, just not to unflatten the device tree,
what do you think?

If it is ok, I will add a fix patch on top of this patch set.

Thanks
Hanjun

quoted

quoted

- otherwise, ACPI will be used as a fallback if the device tree turns out
  to lack a platform description; the heuristic to decide this is whether
  /chosen is the only node present at depth 1

CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Will Deacon <redacted>
CC: Rafael J. Wysocki <redacted>
Acked-by: Olof Johansson <redacted>
Acked-by: Grant Likely <redacted>
Tested-by: Timur Tabi <redacted>
Signed-off-by: Al Stone <redacted>
Signed-off-by: Graeme Gregory <redacted>
Signed-off-by: Hanjun Guo <redacted>
Signed-off-by: Ard Biesheuvel <redacted>
---
 Documentation/kernel-parameters.txt |  3 ++-
 arch/arm64/include/asm/acpi.h       |  7 +++++
 arch/arm64/kernel/acpi.c            | 52 +++++++++++++++++++++++++++++++++----
 3 files changed, 56 insertions(+), 6 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index bfcb1a6..d6c35a7 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt

@@ -165,7 +165,7 @@ multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
 bytes respectively. Such letter suffixes can also be entirely omitted.


-     acpi=           [HW,ACPI,X86]
+     acpi=           [HW,ACPI,X86,ARM64]
                      Advanced Configuration and Power Interface
                      Format: { force | off | strict | noirq | rsdt }
                      force -- enable ACPI if default was off

@@ -175,6 +175,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                              strictly ACPI specification compliant.
                      rsdt -- prefer RSDT over (default) XSDT
                      copy_dsdt -- copy DSDT to memory
+                     For ARM64, ONLY "acpi=off" or "acpi=force" are available

                      See also Documentation/power/runtime_pm.txt, pci=noacpi

diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
index 40e0924..c5a9b97 100644
--- a/arch/arm64/include/asm/acpi.h
+++ b/arch/arm64/include/asm/acpi.h

@@ -39,6 +39,13 @@ static inline void disable_acpi(void)
      acpi_noirq = 1;
 }

+static inline void enable_acpi(void)
+{
+     acpi_disabled = 0;
+     acpi_pci_disabled = 0;
+     acpi_noirq = 0;
+}
+
 /*
  * It's used from ACPI core in kdump to boot UP system with SMP kernel,
  * with this check the ACPI core will not override the CPU index

diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index 7abac24..2269e30 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c

@@ -22,15 +22,49 @@
 #include <linux/irq.h>
 #include <linux/irqdomain.h>
 #include <linux/memblock.h>
+#include <linux/of_fdt.h>
 #include <linux/smp.h>

-int acpi_noirq;                      /* skip ACPI IRQ initialization */
-int acpi_disabled;
+int acpi_noirq = 1;          /* skip ACPI IRQ initialization */
+int acpi_disabled = 1;
 EXPORT_SYMBOL(acpi_disabled);

-int acpi_pci_disabled;               /* skip ACPI PCI scan and IRQ initialization */
+int acpi_pci_disabled = 1;   /* skip ACPI PCI scan and IRQ initialization */
 EXPORT_SYMBOL(acpi_pci_disabled);

+static bool param_acpi_off __initdata;
+static bool param_acpi_force __initdata;
+
+static int __init parse_acpi(char *arg)
+{
+     if (!arg)
+             return -EINVAL;
+
+     /* "acpi=off" disables both ACPI table parsing and interpreter */
+     if (strcmp(arg, "off") == 0)
+             param_acpi_off = true;
+     else if (strcmp(arg, "force") == 0) /* force ACPI to be enabled */
+             param_acpi_force = true;
+     else
+             return -EINVAL; /* Core will print when we return error */
+
+     return 0;
+}
+early_param("acpi", parse_acpi);
+
+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;
+}
+
 /*
  * __acpi_map_table() will be called before page_init(), so early_ioremap()
  * or early_memremap() should be called here to for ACPI table mapping.

@@ -83,10 +117,18 @@ static int __init acpi_parse_fadt(struct acpi_table_header *table)
  */
 void __init acpi_boot_table_init(void)
 {
-     /* If acpi_disabled, bail out */
-     if (acpi_disabled)
+     /*
+      * 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;

+     enable_acpi();
+
      /* Initialize the ACPI boot-time table parser. */
      if (acpi_table_init()) {
              disable_acpi();
--

1.9.1

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