Re: [PATCH v10 08/21] ARM64 / ACPI: Introduce early_param "acpi=" to enable/disable ACPI

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 18 March 2015 at 12:35, Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote:
> On Wed, Mar 11, 2015 at 12:39:34PM +0000, Hanjun Guo wrote:
>> From: Al Stone <al.stone@linaro.org>
>>
>> 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 think we are all in agreement on the policy, we only need to make
disable_acpi() conditional on whether acpi_param_force is set


>> - 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 <will.deacon@arm.com>
>> CC: Rafael J. Wysocki <rjw@rjwysocki.net>
>> Acked-by: Olof Johansson <olof@lixom.net>
>> Acked-by: Grant Likely <grant.likely@linaro.org>
>> Tested-by: Timur Tabi <timur@codeaurora.org>
>> Signed-off-by: Al Stone <al.stone@linaro.org>
>> Signed-off-by: Graeme Gregory <graeme.gregory@linaro.org>
>> Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> ---
>>  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
>>
>>