Re: [PATCH v2 1/8] arm64: move acpi/dt decision earlier in boot process

[Aleksey Makarov <aleksey.makarov@linaro.org>]

Hi Matthias,

On 02/24/2016 09:22 PM, Matthias Brugger wrote:
> 
> 
> On 24/02/16 18:10, Aleksey Makarov wrote:
>> From: Leif Lindholm <leif.lindholm@linaro.org>
>>
>> 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 <leif.lindholm@linaro.org>
>> Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
>> ---
>>   arch/arm64/kernel/acpi.c | 62 +++++++++++++++++++++++-------------------------
>>   1 file changed, 30 insertions(+), 32 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
>> index d1ce8e2..3faa323 100644
>> --- a/arch/arm64/kernel/acpi.c
>> +++ b/arch/arm64/kernel/acpi.c
>> @@ -41,26 +41,8 @@ EXPORT_SYMBOL(acpi_disabled);
>>   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)
>> @@ -74,6 +56,35 @@ static int __init dt_scan_depth1_nodes(unsigned long node,
>>       return 0;
>>   }
>>
>> +static int __init parse_acpi(char *arg)
>> +{
>> +    if (!arg)
>> +        return -EINVAL;
>> +
>> +    /*
>> +     * 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 (strcmp(arg, "off") == 0)
>> +        return 0;
>> +    else if (strcmp(arg, "force") == 0)
>> +        param_acpi_force = true;
>> +    else if (of_scan_flat_dt(dt_scan_depth1_nodes, NULL))
> 
> I think we should strcmp for "on" here and return an error on other values. IMHO an update to Documentation/kernel-parameters.txt would be convenient.

Actually this patch is not correct at all.

on x86:
- if default is off then "acpi=force" enables it.
- if default is on  then "acpi=off"   disables it.

on ARM64 by default OF is preferred to ACPI, but ACPI is used if OF does not provide any nontrivial data.
So we need both "force" and "off"
- "acpi=force" forces ACPI,
- "acpi=off" disables ACPI

The patch makes incorrect code transformation, it changes the default behaviour.

This patch should just be dropped.  The rest of the patchset does not depend on it.

> I still wonder if we really want to change the default to ACPI disabled.
> But that's a decision the maintainers have to take.

I did not realize that the patch changes default.

Thank you
Aleksey Makarov

> Regards,
> Matthias
> 
>> +        return 0;
>> +
>> +    /*
>> +     * ACPI is disabled at this point. Enable it in order to parse
>> +     * the ACPI tables and carry out sanity checks
>> +     */
>> +    enable_acpi();
>> +
>> +    return 0;
>> +}
>> +
>> +early_param("acpi", parse_acpi);
>> +
>>   /*
>>    * __acpi_map_table() will be called before page_init(), so early_ioremap()
>>    * or early_memremap() should be called here to for ACPI table mapping.
>> @@ -181,23 +192,10 @@ out:
>>    */
>>   void __init acpi_boot_table_init(void)
>>   {
>> -    /*
>> -     * 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)))
>> +    if (acpi_disabled)
>>           return;
>>
>>       /*
>> -     * ACPI is disabled at this point. Enable it in order to parse
>> -     * the ACPI tables and carry out sanity checks
>> -     */
>> -    enable_acpi();
>> -
>> -    /*
>>        * If ACPI tables are initialized and FADT sanity checks passed,
>>        * leave ACPI enabled and carry on booting; otherwise disable ACPI
>>        * on initialization error.
>>