This change introduces the runtime pm support on imx serial
driver. The objective is to be able to idle the uart
port whenever it is not in use while still being able
to wake it up when needed. The key changes in this patch are:
1. Move the clock handling to runtime pm. Both, ipg and per,
are now handled in the suspend and resume callbacks. Only
enabling and disabling the clocks are handled in runtime
suspend and resume, so we are able to use runtime pm
in IRQ context.
2. Clocks are prepared in probe and unprepared in remove,
so we do not need to prepare (may sleep) in runtime pm.
3. We mark the device activity based on uart and console
callbacks. Whenever the device is needed and we want to
access registers, we runtime_pm_get and then mark its
last usage when we are done. This is done also across
IRQs and DMA callbacks.
4. We reuse the infrastructure in place for suspend and
resume, so we do not need to redo wakeup configuration,
or context save and restore.

After this change, the clocks are still sane, in the sense
of having balanced clock prepare and enable.

Cc: Fabio Estevam <festevam@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <redacted>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>
---
 drivers/tty/serial/imx.c | 224 +++++++++++++++++++++++++++++++++++++----------
 1 file changed, 178 insertions(+), 46 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 50abb60..9447a55 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c

@@ -39,6 +39,9 @@
 #include <linux/of_device.h>
 #include <linux/io.h>
 #include <linux/dma-mapping.h>
+#include <linux/pm.h>
+#include <linux/pm_runtime.h>
+#include <linux/pm_wakeup.h>
 
 #include <asm/irq.h>
 #include <linux/platform_data/serial-imx.h>

@@ -219,6 +222,7 @@ struct imx_port {
 	unsigned int            saved_reg[10];
 	bool			context_saved;
 
+	struct device		*dev;