On 16 September 2014 21:52, Russell King - ARM Linux
<linux@xxxxxxxxxxxxxxxx> wrote:
> On Tue, Sep 16, 2014 at 08:25:25PM +0200, Ulf Hansson wrote:
>> On 16 September 2014 14:59, Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx> wrote:
>> > The AMBA bus driver defines runtime Power Management functions which
>> > disable and unprepare AMBA bus clock. This is problematic for runtime PM
>> > because unpreparing a clock might sleep so it is not interrupt safe.
>> >
>> > However some drivers may want to implement runtime PM functions in
>> > interrupt-safe way (see pm_runtime_irq_safe()). In such case the AMBA
>> > bus driver should only disable/enable the clock in runtime suspend and
>> > resume callbacks.
>> >
>> > Detect the device driver behavior after calling its probe function and
>> > store it. During runtime suspend/resume deal with clocks according to
>> > stored value.
>> >
>> > Signed-off-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>
>> > ---
>> > drivers/amba/bus.c | 29 +++++++++++++++++++++++++----
>> > include/linux/amba/bus.h | 1 +
>> > 2 files changed, 26 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
>> > index 3cf61a127ee5..e8fd5706954f 100644
>> > --- a/drivers/amba/bus.c
>> > +++ b/drivers/amba/bus.c
>> > @@ -94,8 +94,18 @@ static int amba_pm_runtime_suspend(struct device *dev)
>> > struct amba_device *pcdev = to_amba_device(dev);
>> > int ret = pm_generic_runtime_suspend(dev);
>> >
>> > - if (ret == 0 && dev->driver)
>> > - clk_disable_unprepare(pcdev->pclk);
>> > + if (ret == 0 && dev->driver) {
>> > + /*
>> > + * Drivers should not change pm_runtime_irq_safe()
>> > + * after probe.
>> > + */
>> > + WARN_ON(pcdev->irq_safe != pm_runtime_is_irq_safe(dev));
>>
>> Do we really need a WARN_ON here. Driver shouldn't update their
>> irq_safe value dynamically, right!?
>
> The driver shouldn't update it dynamically, and this makes sure *that*
> is enforced since we end up depending on that property. Hence the
> check is sensible (and I even suggested it.)
The WARN_ON could be nice to have, but I think this is a task for PM
core to handle.
Copying flags shouldn't be needed for each an every instance of a
driver/bus that manage irq_safe devices. That's my main point.
>
>> > +
>> > + if (pcdev->irq_safe)
>> > + clk_disable(pcdev->pclk);
>>
>> Since the irq_safe flag, could be considered as a special case, an
>> option for these cases - could be to leave the clock to be entirely
>> handled from the driver's runtime PM callback instead.
>
> Too many sub-clauses to make much sense of that statement.
Sorry, agree. :-)
>
> I don't want drivers messing around with this stuff. This is the /bus/
> clock, not a device specific clock.
For irq_safe devices, driver's will need to handle the
clk_prepare|unprepare during system PM anyway. That's the reason to
why I suggested this.
On the other hand I agree with you, it's a bus clock...
Kind regards
Uffe
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