[pm-core][PATCH v3 01/21] OMAP4: PM: Add omap WakeupGen module support

[Colin Cross]

On Sat, Apr 2, 2011 at 2:40 AM, Santosh Shilimkar
<santosh.shilimkar at ti.com> wrote:
> On 4/2/2011 11:40 AM, Colin Cross wrote:
>>
>> On Mon, Mar 28, 2011 at 2:22 AM, Santosh Shilimkar
>> <santosh.shilimkar at ti.com>  wrote:
>>>
>>> This patch adds OMAP WakeupGen support. The WakeupGen unit is responsible
>>> for generating wakeup event from the incoming interrupts and enable bits.
>>> The WakeupGen is implemented in MPU Always-On power domain. During normal
>>> operation, WakeupGen delivers external interrupts directly to the GIC.
>>> When the CPUx asserts StandbyWFI, indicating it wants to enter lowpower
>>> state, the Standby Controller checks with the WakeupGen unit using the
>>> idlereq/idleack handshake to make sure there is no incoming interrupts.
>>> The GIC and WakeupGen needs to be kept in synchronisation for proper
>>> interrupt functioning.
>>>
>>> Hence this patch hooks up the omap WakeupGen mask/unmask along with GIC
>>> using
>>> architecture specific hooks.
>>>
>>> Signed-off-by: Santosh Shilimkar<santosh.shilimkar at ti.com>
>>> Cc: Kevin Hilman<khilman at ti.com>
>>
>> <snip>
>>
>>> +static void _wakeupgen_clear(unsigned int irq)
>>> +{
>>> +       unsigned int cpu = smp_processor_id();
>>> +       u32 val, bit_number;
>>> +       u8 i;
>>> +
>>> +       if (_wakeupgen_get_irq_info(irq,&bit_number,&i))
>>> +               return;
>>> +
>>> +       val = wakeupgen_readl(i, cpu);
>>> +       val&= ~BIT(bit_number);
>>> +       wakeupgen_writel(val, i, cpu);
>>> +}
>>> +
>>> +static void _wakeupgen_set(unsigned int irq)
>>> +{
>>> +       unsigned int cpu = smp_processor_id();
>>> +       u32 val, bit_number;
>>> +       u8 i;
>>> +
>>> +       if (_wakeupgen_get_irq_info(irq,&bit_number,&i))
>>> +               return;
>>> +
>>> +       val = wakeupgen_readl(i, cpu);
>>> +       val |= BIT(bit_number);
>>> +       wakeupgen_writel(val, i, cpu);
>>> +}
>>
>> Since you already call these from a function that takes a bool as an
>> argument, using a bool argument here instead of duplicating everything
>> for set and clear would be simpler.
>>
> First version of this patch has this done under single function as you
> said. Kevin suggested to have separate functions for better readability.
>
>> <snip>
>>
>>> +/*
>>> + * Architecture specific Mask extensiom
>>> + */
>>> +static void wakeupgen_mask(struct irq_data *d)
>>> +{
>>> +       spin_lock(&wakeupgen_lock);
>>> +       _wakeupgen_clear(d->irq);
>>> +       spin_unlock(&wakeupgen_lock);
>>> +}
>>> +
>>> +/*
>>> + * Architecture specific Unmask extensiom
>>> + */
>>> +static void wakeupgen_unmask(struct irq_data *d)
>>> +{
>>> +
>>> +       spin_lock(&wakeupgen_lock);
>>> +       _wakeupgen_set(d->irq);
>>> +       spin_unlock(&wakeupgen_lock);
>>> +}
>>> +
>>> +#ifdef CONFIG_PM
>>> +/*
>>> + * Architecture specific set_wake extension
>>> + */
>>> +static int wakeupgen_set_wake(struct irq_data *d, unsigned int on)
>>> +{
>>> +       spin_lock(&wakeupgen_lock);
>>> +       if (on)
>>> +               _wakeupgen_set(d->irq);
>>> +       else
>>> +               _wakeupgen_clear(d->irq);
>>> +       spin_unlock(&wakeupgen_lock);
>>> +
>>> +       return 0;
>>> +}
>>> +
>>> +#else
>>> +#define wakeupgen_set_wake     NULL
>>> +#endif
>>
>> I don't think these are correct, and it probably only works at all due
>> to lazy disabling of interrupts during suspend.
>>
>> First, unless I'm missing some code somewhere, all interrupts are
>> still enabled during suspend.  Any interrupt that has had enable_irq
>> on it resulted in a call to wakeupgen_unmask, but when disable_irq is
>> called on all the interrupts during suspend, masking is delayed until
>> an interrupt is delivered.  If no interrupt is delivered, all enabled
>> irqs will still be enabled in the wakeupgen module in suspend, and
>> they will all wake the device out of suspend.
>>
> During suspend it's expected that the drivers disables there interrupts
> as part of suspend hooks. One can used "set_wake" API's to
> enable/disable wakeups from suspend.

But because of lazy masking, disabling an interrupt is not the same as
masking.  None of the interrupts will get masked, and they will all
act as wakeup interrupts, even if enable_irq_wake was never called on
it.

>
>> Second, it is possible for a wake interrupt that should be enabled to
>> end up disabled in suspend.  Consider the following calls that occur
>> in a driver during its suspend handler:
>>
>> enable_irq_wake
>>   ...
>>   wakeupgen_unmask (irq is now unmasked)
>> disable_irq (lazy disable, wakeupgen_mask is not called, irq is still
>> unmasked)
>> <irq occurs>
>> handle_level_irq
>>   ...
>>   wakeupgen_mask (irq is now masked)
>>
>> The irq will never get unmasked because it is marked disabled, and the
>> irq will not wake the device from suspend.
>>
>> wakeupgen_set_wake needs to set or clear bits in memory, and then
>> those suspend masks need to be copied into the wakeupgen registers
>> very late in suspend, after interrupts have been disabled at the cpu.
>> I think syscore_ops is the right place.
>>
> This is a good point about lazy disabling. Copy to memory happens
> already as part of save in SAR layout.
> Will think over this one. Thanks for bringing this point here.

The key is that mask/unmask and set_wake must act on different mask
data - mask/unmask must take effect immediately, so they must write to
the mask registers, but set_wake takes effect only during suspend, so
it must write to a copy of the mask registers that gets switched in
during suspend.

> Regards
> Santosh
>