Patchwork rtc: Set wakeup capability for I2C and SPI RTC drivers

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Submitter Anton Vorontsov
Date Aug. 27, 2009, 6:22 p.m.
Message ID <20090827182207.GA7358@oksana.dev.rtsoft.ru>
Download mbox | patch
Permalink /patch/32277/
State Accepted
Headers show

Comments

Anton Vorontsov - Aug. 27, 2009, 6:22 p.m.
RTC core won't allow wakeup alarms to be set if RTC devices' parent
(i.e. i2c_client or spi_device) isn't wakeup capable.

For I2C devices there is I2C_CLIENT_WAKE flag exists that we can pass
via board info, and if set, I2C core will initialize wakeup capability.
For SPI devices there is no such flag at all.

I believe that it's not platform code responsibility to allow or
disallow wakeups, instead, drivers themselves should set the capability
if a device can trigger wakeups.

That's what drivers/base/power/sysfs.c says:

 * It is the responsibility of device drivers to enable (or disable)
 * wakeup signaling as part of changing device power states, respecting
 * the policy choices provided through the driver model.

I2C and SPI RTC devices send wakeup events via interrupt lines, so we
should set the wakeup capability if IRQ is routed.

Ideally we should also check irq for wakeup capability before setting
device's capability, i.e.

	if (can_irq_wake(irq))
		device_set_wakeup_capable(&client->dev, 1);

But there is no can_irq_wake() call exist, and it is not that trivial
to implement it for all interrupts controllers and complex/cascaded
setups.

drivers/base/power/sysfs.c also covers these cases:

 * Devices may not be able to generate wakeup events from all power
 * states.  Also, the events may be ignored in some configurations;
 * for example, they might need help from other devices that aren't
 * active

So there is no guarantee that wakeup will actually work, and so I think
there is no point in being pedantic wrt checking IRQ wakeup capability.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
---
 drivers/rtc/rtc-ds1305.c |    2 ++
 drivers/rtc/rtc-ds1307.c |    2 ++
 drivers/rtc/rtc-ds1374.c |    2 ++
 3 files changed, 6 insertions(+), 0 deletions(-)
David Brownell - Aug. 27, 2009, 9:52 p.m.
NAK; see details below

On Thursday 27 August 2009, Anton Vorontsov wrote:
> RTC core won't allow wakeup alarms to be set if RTC devices' parent
> (i.e. i2c_client or spi_device) isn't wakeup capable.

Quite rightly so ... being wakeup-capable is config-specific.


> For I2C devices there is I2C_CLIENT_WAKE flag exists that we can pass
> via board info, and if set, I2C core will initialize wakeup capability.
> For SPI devices there is no such flag at all.

So why not add it for SPI?  If it's an issue, it's not
unique to RTC devices.

 
> I believe that it's not platform code responsibility to allow or
> disallow wakeups, instead, drivers themselves should set the capability
> if a device can trigger wakeups.

Drivers can't generally know if that's possible though.
They need to be told that it is, by platform code.

Most devices can't issue wakeup events.

 
> That's what drivers/base/power/sysfs.c says:
> 
>  * It is the responsibility of device drivers to enable (or disable)
>  * wakeup signaling as part of changing device power states, respecting
>  * the policy choices provided through the driver model.
> 
> I2C and SPI RTC devices send wakeup events via interrupt lines, so we
> should set the wakeup capability if IRQ is routed.

Re-read the quoted sentence.  You're saying that policy
choices should be hard-wired into the driver; contrary
to that quote.  (In this case the choice is one that
platform code must report, and which the hardware
designer made:  if the device can issue wakeup events.)  


> Ideally we should also check irq for wakeup capability before setting
> device's capability, i.e.
> 
> 	if (can_irq_wake(irq))
> 		device_set_wakeup_capable(&client->dev, 1);
> 
> But there is no can_irq_wake() call exist, and it is not that trivial
> to implement it for all interrupts controllers and complex/cascaded
> setups.

That is why platform code should device_init_wakeup() and
drivers should check device_can_wakeup(dev) ...


> drivers/base/power/sysfs.c also covers these cases:
> 
>  * Devices may not be able to generate wakeup events from all power
>  * states.  Also, the events may be ignored in some configurations;
>  * for example, they might need help from other devices that aren't
>  * active
> 
> So there is no guarantee that wakeup will actually work, 

Yes there is ... it's only **exceptional** cases where it can't
work.  Your patch would make it routine that those flags be
unreliable; pretty nasty.
Anton Vorontsov - Aug. 27, 2009, 11:19 p.m.
On Thu, Aug 27, 2009 at 02:52:36PM -0700, David Brownell wrote:
[...]
> > I believe that it's not platform code responsibility to allow or
> > disallow wakeups, instead, drivers themselves should set the capability
> > if a device can trigger wakeups.
> 
> Drivers can't generally know if that's possible though.
> They need to be told that it is, by platform code.

Um? Of course they know, DS1374 device driver knows that DS1374
chips can issue wakeups, what it doesn't know is if that wakeup
event will trigger CPU resume/power-up.

And even platform code doesn't know that. For example, on PowerPC
CPUs there could be several 'suspend' states, some allow wakeup
on particular IRQs, some don't. In some cases wakeup event will be
ignored, in other cases it will take effect. The suspend mode
depends on user's decision ('echo <mode> > /sys/power/state').

> Most devices can't issue wakeup events.

The device drivers I modified know that devices can issue wakeup
events.

> > That's what drivers/base/power/sysfs.c says:
> > 
> >  * It is the responsibility of device drivers to enable (or disable)
> >  * wakeup signaling as part of changing device power states, respecting
> >  * the policy choices provided through the driver model.
> > 
> > I2C and SPI RTC devices send wakeup events via interrupt lines, so we
> > should set the wakeup capability if IRQ is routed.
> 
> Re-read the quoted sentence.  You're saying that policy
> choices should be hard-wired into the driver; contrary
> to that quote.  (In this case the choice is one that
> platform code must report, and which the hardware
> designer made:  if the device can issue wakeup events.)

The patch doesn't hard-wire the policy, quite the contrary: it
removes the "can't do wakeup" policy.

I'm just adding device_set_wakeup_capable() calls, telling everybody
that the devices can issue wakeup events (and they truly can).

Yes, it could be that the IRQ line is wired not to a CPU, but
to some power switch, and so nobody pass any IRQs to the drivers.
In that case platform-specific I2C_CLIENT_WAKE may be useful.

> > Ideally we should also check irq for wakeup capability before setting
> > device's capability, i.e.
> > 
> > 	if (can_irq_wake(irq))
> > 		device_set_wakeup_capable(&client->dev, 1);
> > 
> > But there is no can_irq_wake() call exist, and it is not that trivial
> > to implement it for all interrupts controllers and complex/cascaded
> > setups.
> 
> That is why platform code should device_init_wakeup() and
> drivers should check device_can_wakeup(dev) ...

They should (and do) check may_wakeup() (i.e. should_wakeup) before
suspending, not can_wakeup().

static int ds1374_suspend(struct i2c_client *client, pm_message_t state)
{
        if (client->irq >= 0 && device_may_wakeup(&client->dev))
                enable_irq_wake(client->irq);
        return 0;
}

(quite funny, they issue enable_irq_wake(), assuming that otherwise
IRQ line won't trigger CPU wakeup. But in reality, there are interrupt
controllers that you can't control in that regard: any IRQ activity
will always resume CPU. And so 'echo disable > /sys/.../wakeup' won't
guarantee anything. Unreliable, nasty? Could be.)

> > drivers/base/power/sysfs.c also covers these cases:
> > 
> >  * Devices may not be able to generate wakeup events from all power
> >  * states.  Also, the events may be ignored in some configurations;
> >  * for example, they might need help from other devices that aren't
> >  * active
> > 
> > So there is no guarantee that wakeup will actually work, 
> 
> Yes there is ... it's only **exceptional** cases where it can't
> work.  Your patch would make it routine that those flags be
> unreliable; pretty nasty.

It's not exceptional at all, you really can't tell if device's wakeup
event will take any effect. It depends on so many factors that it's
virtually impossible to account them all. And hiding wakeup capability
only because you aren't sure _is_ policy hard-wiring, no?

Thanks,
Anton Vorontsov - Aug. 28, 2009, 12:30 a.m.
On Fri, Aug 28, 2009 at 03:19:25AM +0400, Anton Vorontsov wrote:
[...]
> > That is why platform code should device_init_wakeup() and
> > drivers should check device_can_wakeup(dev) ...
> 
> They should (and do) check may_wakeup() (i.e. should_wakeup) before
> suspending, not can_wakeup().
> 
> static int ds1374_suspend(struct i2c_client *client, pm_message_t state)
> {
>         if (client->irq >= 0 && device_may_wakeup(&client->dev))
>                 enable_irq_wake(client->irq);
>         return 0;
> }
> 
> (quite funny, they issue enable_irq_wake(), assuming that otherwise
> IRQ line won't trigger CPU wakeup. But in reality, there are interrupt
> controllers that you can't control in that regard: any IRQ activity
> will always resume CPU. And so 'echo disable > /sys/.../wakeup' won't
> guarantee anything. Unreliable, nasty? Could be.)

BTW, of course we can fix this by masking interrupts before
suspending, but nobody actually do this (but should, I think).

And if RTC's IRQ is wired to power switch you're in trouble
without any way to fix this.

Patch

diff --git a/drivers/rtc/rtc-ds1305.c b/drivers/rtc/rtc-ds1305.c
index 2736b11..e256c03 100644
--- a/drivers/rtc/rtc-ds1305.c
+++ b/drivers/rtc/rtc-ds1305.c
@@ -780,6 +780,8 @@  static int __devinit ds1305_probe(struct spi_device *spi)
 					spi->irq, status);
 			goto fail1;
 		}
+
+		device_set_wakeup_capable(&spi->dev, 1);
 	}
 
 	/* export NVRAM */
diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
index 47a93c0..87097d4 100644
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -881,6 +881,8 @@  read_rtc:
 				"unable to request IRQ!\n");
 			goto exit_irq;
 		}
+
+		device_set_wakeup_capable(&client->dev, 1);
 		set_bit(HAS_ALARM, &ds1307->flags);
 		dev_dbg(&client->dev, "got IRQ %d\n", client->irq);
 	}
diff --git a/drivers/rtc/rtc-ds1374.c b/drivers/rtc/rtc-ds1374.c
index 713f7bf..5317bbc 100644
--- a/drivers/rtc/rtc-ds1374.c
+++ b/drivers/rtc/rtc-ds1374.c
@@ -383,6 +383,8 @@  static int ds1374_probe(struct i2c_client *client,
 			dev_err(&client->dev, "unable to request IRQ\n");
 			goto out_free;
 		}
+
+		device_set_wakeup_capable(&client->dev, 1);
 	}
 
 	ds1374->rtc = rtc_device_register(client->name, &client->dev,