mmc: sdio: support suspend/resume while runtime suspended

Bring SDIO devices back to full power before their suspend
handler is invoked.

Doing so ensures that SDIO suspend/resume semantics are
maintained (drivers still get to decide whether their
card should be removed or kept during system suspend,
and at what power state), and that SDIO suspend/resume
execution paths are unchanged.

This is achieved by resuming a runtime-suspended SDIO device
in its ->prepare() PM callback (similary to the PCI subsystem).

Since the PM core always increments the run-time usage
counter before calling the ->prepare() callback and decrements
it after calling the ->complete() callback, it is guaranteed
that when the system will come out of suspend, our device's
power state will reflect its runtime PM usage counter.

Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>
Tested-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

1 files changed, 29 insertions, 0 deletions

diff --git a/drivers/mmc/core/sdio_bus.c b/drivers/mmc/core/sdio_bus.c
index 36374834fcff..2716c7ab6bbf 100644
--- a/drivers/mmc/core/sdio_bus.c
+++ b/drivers/mmc/core/sdio_bus.c
@@ -189,12 +189,41 @@ out:
 
 #ifdef CONFIG_PM_RUNTIME
 
+static int sdio_bus_pm_prepare(struct device *dev)
+{
+        /*
+         * Resume an SDIO device which was suspended at run time at this
+         * point, in order to allow standard SDIO suspend/resume paths
+         * to keep working as usual.
+         *
+         * Ultimately, the SDIO driver itself will decide (in its
+         * suspend handler, or lack thereof) whether the card should be
+         * removed or kept, and if kept, at what power state.
+         *
+         * At this point, PM core have increased our use count, so it's
+         * safe to directly resume the device. After system is resumed
+         * again, PM core will drop back its runtime PM use count, and if
+         * needed device will be suspended again.
+         *
+         * The end result is guaranteed to be a power state that is
+         * coherent with the device's runtime PM use count.
+         *
+         * The return value of pm_runtime_resume is deliberately unchecked
+         * since there is little point in failing system suspend if a
+         * device can't be resumed.
+         */
+        pm_runtime_resume(dev);
+
+        return 0;
+}
+
 static const struct dev_pm_ops sdio_bus_pm_ops = {
         SET_RUNTIME_PM_OPS(
                 pm_generic_runtime_suspend,
                 pm_generic_runtime_resume,
                 pm_generic_runtime_idle
         )
+        .prepare = sdio_bus_pm_prepare,
 };
 
 #define SDIO_PM_OPS_PTR (&sdio_bus_pm_ops)