spi/omap2_mcspi.c: Force CS to be in inactive state after off-mode transition

When SPI wake up from OFF mode, CS is in the wrong state: force it to the
inactive state.

During the system life, I monitored the CS behavior using a oscilloscope.
I also activated debug in omap2_mcspi, so I saw when driver disable the clocks
and restore context when device is not used.Each time the CS was in the correct
state.  It was only when system was put suspend to ram with off-mode activated
that on resume the CS was in wrong state( ie activated).

Changelog:
* Change from v1 to v2:
  - Rebase on linus/master (after 2.6.37-rc1)
  - Do some clean-up and fix indentation on both patches
  - Add more explanations for patch 2

* Change from v2 to v3:
  - Use directly resume function of spi_master instead of using function
  - from spi_device as Grant Likely pointed it out.
  - Force this transition explicitly for each CS used by a device.

* Change from v3 to v4:
  - Patch clean-up according to Kevin Hilman and checkpatch.
  - Now force CS to be in inactive state only if it was inactive when it was
    suspended.

* Change from v4 to v5:
  - Rebase on linus/master (after 2.6.37-rc3)
  - Collapse some lines as pointed by Grant Likely
  - Fix a spelling

* Change from v5 to v6:
  - Rebase on linus/master (after 2.6.37-rc7)
  - Use CONFIG_SUSPEND instead of CONFIG_PM
  - Didn't use legacy PM methods anymore. Instead, add a struct dev_pm_ops and
    add the resume method there.
  - Fix multi-line comment style

* Change from v6 to v7:
  - Rebase on linus/master (after 2.6.37-rc8)
  - Drop an extra line
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Reviewed-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/omap2_mcspi.c

@@ -1305,10 +1305,49 @@ static int __exit omap2_mcspi_remove(struct platform_device *pdev)
 /* work with hotplug and coldplug */
 MODULE_ALIAS("platform:omap2_mcspi");
 
+#ifdef	CONFIG_SUSPEND
+/*
+ * When SPI wake up from off-mode, CS is in activate state. If it was in
+ * unactive state when driver was suspend, then force it to unactive state at
+ * wake up.
+ */
+static int omap2_mcspi_resume(struct device *dev)
+{
+	struct spi_master	*master = dev_get_drvdata(dev);
+	struct omap2_mcspi	*mcspi = spi_master_get_devdata(master);
+	struct omap2_mcspi_cs *cs;
+
+	omap2_mcspi_enable_clocks(mcspi);
+	list_for_each_entry(cs, &omap2_mcspi_ctx[master->bus_num - 1].cs,
+			    node) {
+		if ((cs->chconf0 & OMAP2_MCSPI_CHCONF_FORCE) == 0) {
+
+			/*
+			 * We need to toggle CS state for OMAP take this
+			 * change in account.
+			 */
+			MOD_REG_BIT(cs->chconf0, OMAP2_MCSPI_CHCONF_FORCE, 1);
+			__raw_writel(cs->chconf0, cs->base + OMAP2_MCSPI_CHCONF0);
+			MOD_REG_BIT(cs->chconf0, OMAP2_MCSPI_CHCONF_FORCE, 0);
+			__raw_writel(cs->chconf0, cs->base + OMAP2_MCSPI_CHCONF0);
+		}
+	}
+	omap2_mcspi_disable_clocks(mcspi);
+	return 0;
+}
+#else
+#define	omap2_mcspi_resume	NULL
+#endif
+
+static const struct dev_pm_ops omap2_mcspi_pm_ops = {
+	.resume = omap2_mcspi_resume,
+};
+
 static struct platform_driver omap2_mcspi_driver = {
 	.driver = {
 		.name =		"omap2_mcspi",
 		.owner =	THIS_MODULE,
+		.pm =		&omap2_mcspi_pm_ops
 	},
 	.remove =	__exit_p(omap2_mcspi_remove),
 };