On 16 September 2014 21:52, Russell King - ARM Linux
[off-list ref] wrote:

On Tue, Sep 16, 2014 at 08:25:25PM +0200, Ulf Hansson wrote:

quoted

On 16 September 2014 14:59, Krzysztof Kozlowski [off-list ref] wrote:

quoted

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 <redacted>
---
 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.

quoted

quoted

+
+               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