[PATCH v2] x86: Bypass legacy PIC and PIT in ACPI hardware reduced mode

[PATCH v2] x86: Bypass legacy PIC and PIT in ACPI hardware reduced mode

[Li, Aubrey]

On a platform in ACPI Hardware-reduced mode, the legacy PIC and PIT
may not be initialized even though they may be present in silicon.
Touching these legacy components causes unexpected result on system.

On Bay Trail-T(ASUS-T100) platform, touching these legacy components
blocks platform hardware low idle power state(S0ix) during system
suspend. So we should bypass them in ACPI hardware reduced mode.

Suggested-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Li Aubrey <aubrey.li@linux.intel.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Alan Cox <alan@linux.intel.com>
---
 arch/x86/kernel/acpi/boot.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index b9e30da..1e5a7865 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -1343,6 +1343,24 @@ static int __init dmi_ignore_irq0_timer_override(const struct dmi_system_id *d)
 }
 
 /*
+ * ACPI offers an alternative platform interface model that removes
+ * ACPI hardware requirements for platforms that do not implement
+ * the PC Architecture.
+ *
+ * We initialize the Hardware-reduced ACPI model here
+ */
+static void __init acpi_reduced_hw_init(void)
+{
+	/*
+	 * Override x86_init functions and bypass legacy pic
+	 * in Hardware-reduced ACPI mode
+	 */
+	x86_init.timers.timer_init	= x86_init_noop;
+	x86_init.irqs.pre_vector_init	= x86_init_noop;
+	legacy_pic			= &null_legacy_pic;
+}
+
+/*
  * If your system is blacklisted here, but you find that acpi=force
  * works for you, please contact linux-acpi@vger.kernel.org
  */
@@ -1541,6 +1559,9 @@ int __init early_acpi_boot_init(void)
 	 */
 	early_acpi_process_madt();
 
+	if (acpi_gbl_reduced_hardware)
+		acpi_reduced_hw_init();
+
 	return 0;
 }
 
-- 
1.9.1

Re: [PATCH v2] x86: Bypass legacy PIC and PIT in ACPI hardware reduced mode

[Ingo Molnar]

* Li, Aubrey <aubrey.li@linux.intel.com> wrote:

> On a platform in ACPI Hardware-reduced mode, the legacy PIC and PIT
> may not be initialized even though they may be present in silicon.
> Touching these legacy components causes unexpected result on system.

s/causes unexpected result on system/
  causes unexpected results on the system

> 
> On Bay Trail-T(ASUS-T100) platform, touching these legacy components

s/On Bay Trail-T(ASUS-T100) platform/
  On the Bay Trail-T(ASUS-T100) platform

> blocks platform hardware low idle power state(S0ix) during system
> suspend. So we should bypass them in ACPI hardware reduced mode.
> 
> Suggested-by: Arjan van de Ven <arjan@linux.intel.com>
> Signed-off-by: Li Aubrey <aubrey.li@linux.intel.com>
> Cc: Len Brown <len.brown@intel.com>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Cc: Alan Cox <alan@linux.intel.com>
> ---
>  arch/x86/kernel/acpi/boot.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> index b9e30da..1e5a7865 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -1343,6 +1343,24 @@ static int __init dmi_ignore_irq0_timer_override(const struct dmi_system_id *d)
>  }
>  
>  /*
> + * ACPI offers an alternative platform interface model that removes
> + * ACPI hardware requirements for platforms that do not implement
> + * the PC Architecture.
> + *
> + * We initialize the Hardware-reduced ACPI model here
> + */
> +static void __init acpi_reduced_hw_init(void)
> +{
> +	/*
> +	 * Override x86_init functions and bypass legacy pic
> +	 * in Hardware-reduced ACPI mode
> +	 */
> +	x86_init.timers.timer_init	= x86_init_noop;
> +	x86_init.irqs.pre_vector_init	= x86_init_noop;
> +	legacy_pic			= &null_legacy_pic;
> +}
> +
> +/*
>   * If your system is blacklisted here, but you find that acpi=force
>   * works for you, please contact linux-acpi@vger.kernel.org
>   */
> @@ -1541,6 +1559,9 @@ int __init early_acpi_boot_init(void)
>  	 */
>  	early_acpi_process_madt();
>  
> +	if (acpi_gbl_reduced_hardware)
> +		acpi_reduced_hw_init();

Ok, my final bike shed painting job would be to move the 
'acpi_gbl_reduced_hardware' flag check inside acpi_reduced_hw_init(): 
that makes it nicely self-sustained and all in a single place.

With that fixed it looks good to me.

Should I merge it for v4.0 upstream merge, in tip:x86/urgent?

The 'touches hardware in unexpected ways' aspect qualifies it for 
urgent treatment IMO.

Thanks,

	Ingo

Re: [PATCH v2] x86: Bypass legacy PIC and PIT in ACPI hardware reduced mode

[Li, Aubrey]

On 2015/3/11 14:23, Ingo Molnar wrote:
> 
> * Li, Aubrey <aubrey.li@linux.intel.com> wrote:
> 
>> On a platform in ACPI Hardware-reduced mode, the legacy PIC and PIT
>> may not be initialized even though they may be present in silicon.
>> Touching these legacy components causes unexpected result on system.
> 
> s/causes unexpected result on system/
>   causes unexpected results on the system
> 
>>
>> On Bay Trail-T(ASUS-T100) platform, touching these legacy components
> 
> s/On Bay Trail-T(ASUS-T100) platform/
>   On the Bay Trail-T(ASUS-T100) platform
> 
> Ok, my final bike shed painting job would be to move the 
> 'acpi_gbl_reduced_hardware' flag check inside acpi_reduced_hw_init(): 
> that makes it nicely self-sustained and all in a single place.
> 
> With that fixed it looks good to me.

Thanks, I'll cook v3 soon, :-)
> 
> Should I merge it for v4.0 upstream merge, in tip:x86/urgent?
> 
> The 'touches hardware in unexpected ways' aspect qualifies it for 
> urgent treatment IMO.

Currently the unexpected result is that it blocks a low power idle
during suspend. I'm not sure if it can be for x86/urgent. But it would
be nice if it can be a bug-fix in v4.0.

Thanks,
-Aubrey

> 
> Thanks,
> 
> 	Ingo
> 
>