OMAP2+: wd_timer: disable on boot via hwmod postsetup mechanism

The OMAP watchdog timer IP blocks require a specific set of register
writes to occur before they will be disabled[1], even if the device
clocks appear to be disabled in the CM_*CLKEN registers.  In the MPU
watchdog case, failure to execute this reset sequence will eventually
cause the watchdog to reset the OMAP unexpectedly.

Previously, the code to disable this watchdog was manually called from
mach-omap2/devices.c during device initialization.  This causes the
watchdog to be unconditionally disabled for a portion of kernel
initialization.  This should be controllable by the board-*.c files,
since some system integrators will want full watchdog coverage of
kernel initialization.  Also, the watchdog disable code was not
connected to the hwmod shutdown code.  This means that calling
omap_hwmod_shutdown() will not, in fact, disable the watchdog, and the
goal of omap_hwmod_shutdown() is to be able to shutdown any on-chip
OMAP device.

To resolve the latter problem, populate the pre_shutdown pointer in
the watchdog timer hwmod classes with a function that executes the
watchdog shutdown sequence.  This allows the hwmod code to fully
disable the watchdog.

Then, to allow some board files to support watchdog coverage
throughout kernel initialization, add common code to mach-omap2/io.c
to cause the MPU watchdog to be disabled on boot unless a board file
specifically requests it to remain enabled.  Board files can do this
by changing the watchdog timer hwmod's postsetup state between the
omap2_init_common_infrastructure() and omap2_init_common_devices()
function calls.

1. OMAP34xx Multimedia Device Silicon Revision 3.1.x Rev. ZH
   [SWPU222H], Section 16.4.3.6, "Start/Stop Sequence for WDTs (Using
   WDTi.WSPR Register)"
Signed-off-by: NPaul Walmsley <paul@pwsan.com>
Cc: Benoît Cousson <b-cousson@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Charulatha Varadarajan <charu@ti.com>

arch/arm/mach-omap2/devices.c

@@ -33,7 +33,6 @@
 
 #include "mux.h"
 #include "control.h"
-#include "wd_timer.h"
 
 #if defined(CONFIG_VIDEO_OMAP2) || defined(CONFIG_VIDEO_OMAP2_MODULE)
 
@@ -956,26 +955,12 @@ static inline void omap_init_vout(void) {}
 
 /*-------------------------------------------------------------------------*/
 
-static int omap2_disable_wdt(struct omap_hwmod *oh, void *unused)
-{
-	return omap2_wd_timer_disable(oh);
-}
-
-static void __init omap_disable_wdt(void)
-{
-	if (cpu_class_is_omap2())
-		omap_hwmod_for_each_by_class("wd_timer",
-					     omap2_disable_wdt, NULL);
-	return;
-}
-
 static int __init omap2_init_devices(void)
 {
 	/*
 	 * please keep these calls, and their implementations above,
 	 * in alphabetical order so they're easier to sort through.
 	 */
-	omap_disable_wdt();
 	omap_hsmmc_reset();
 	omap_init_audio();
 	omap_init_camera();

arch/arm/mach-omap2/io.c

@@ -361,6 +361,24 @@ void __init omap2_init_common_infrastructure(void)
 #endif
 	omap_hwmod_for_each(_set_hwmod_postsetup_state, &postsetup_state);
 
+	/*
+	 * Set the default postsetup state for unusual modules (like
+	 * MPU WDT).
+	 *
+	 * The postsetup_state is not actually used until
+	 * omap_hwmod_late_init(), so boards that desire full watchdog
+	 * coverage of kernel initialization can reprogram the
+	 * postsetup_state between the calls to
+	 * omap2_init_common_infra() and omap2_init_common_devices().
+	 *
+	 * XXX ideally we could detect whether the MPU WDT was currently
+	 * enabled here and make this conditional
+	 */
+	postsetup_state = _HWMOD_STATE_DISABLED;
+	omap_hwmod_for_each_by_class("wd_timer",
+				     _set_hwmod_postsetup_state,
+				     &postsetup_state);
+
 	omap_pm_if_early_init();
 
 	if (cpu_is_omap2420())

arch/arm/mach-omap2/omap_hwmod_2420_data.c

@@ -23,6 +23,7 @@
 
 #include "cm-regbits-24xx.h"
 #include "prm-regbits-24xx.h"
+#include "wd_timer.h"
 
 /*
  * OMAP2420 hardware module integration data
@@ -312,8 +313,9 @@ static struct omap_hwmod_class_sysconfig omap2420_wd_timer_sysc = {
 };
 
 static struct omap_hwmod_class omap2420_wd_timer_hwmod_class = {
-	.name = "wd_timer",
-	.sysc = &omap2420_wd_timer_sysc,
+	.name		= "wd_timer",
+	.sysc		= &omap2420_wd_timer_sysc,
+	.pre_shutdown	= &omap2_wd_timer_disable
 };
 
 /* wd_timer2 */

arch/arm/mach-omap2/omap_hwmod_2430_data.c

@@ -23,6 +23,7 @@
 
 #include "prm-regbits-24xx.h"
 #include "cm-regbits-24xx.h"
+#include "wd_timer.h"
 
 /*
  * OMAP2430 hardware module integration data
@@ -311,8 +312,9 @@ static struct omap_hwmod_class_sysconfig omap2430_wd_timer_sysc = {
 };
 
 static struct omap_hwmod_class omap2430_wd_timer_hwmod_class = {
-	.name = "wd_timer",
-	.sysc = &omap2430_wd_timer_sysc,
+	.name		= "wd_timer",
+	.sysc		= &omap2430_wd_timer_sysc,
+	.pre_shutdown	= &omap2_wd_timer_disable
 };
 
 /* wd_timer2 */

arch/arm/mach-omap2/omap_hwmod_3xxx_data.c

@@ -26,6 +26,7 @@
 
 #include "prm-regbits-34xx.h"
 #include "cm-regbits-34xx.h"
+#include "wd_timer.h"
 
 /*
  * OMAP3xxx hardware module integration data
@@ -423,8 +424,9 @@ static struct omap_hwmod_class_sysconfig i2c_sysc = {
 };
 
 static struct omap_hwmod_class omap3xxx_wd_timer_hwmod_class = {
-	.name = "wd_timer",
-	.sysc = &omap3xxx_wd_timer_sysc,
+	.name		= "wd_timer",
+	.sysc		= &omap3xxx_wd_timer_sysc,
+	.pre_shutdown	= &omap2_wd_timer_disable
 };
 
 /* wd_timer2 */

arch/arm/mach-omap2/omap_hwmod_44xx_data.c

@@ -29,6 +29,7 @@
 
 #include "cm.h"
 #include "prm-regbits-44xx.h"
+#include "wd_timer.h"
 
 /* Base offset for all OMAP4 interrupts external to MPUSS */
 #define OMAP44XX_IRQ_GIC_START	32
@@ -728,8 +729,9 @@ static struct omap_hwmod_class_sysconfig omap44xx_uart_sysc = {
 };
 
 static struct omap_hwmod_class omap44xx_wd_timer_hwmod_class = {
-	.name = "wd_timer",
-	.sysc = &omap44xx_wd_timer_sysc,
+	.name		= "wd_timer",
+	.sysc		= &omap44xx_wd_timer_sysc,
+	.pre_shutdown	= &omap2_wd_timer_disable
 };
 
 /* wd_timer2 */

arch/arm/mach-omap2/wd_timer.c

@@ -27,7 +27,6 @@
 int omap2_wd_timer_disable(struct omap_hwmod *oh)
 {
 	void __iomem *base;
-	int ret;
 
 	if (!oh) {
 		pr_err("%s: Could not look up wdtimer_hwmod\n", __func__);
@@ -41,14 +40,6 @@ int omap2_wd_timer_disable(struct omap_hwmod *oh)
 		return -EINVAL;
 	}
 
-	/* Enable the clocks before accessing the WDT registers */
-	ret = omap_hwmod_enable(oh);
-	if (ret) {
-		pr_err("%s: Could not enable clocks for %s\n",
-				oh->name, __func__);
-		return ret;
-	}
-
 	/* sequence required to disable watchdog */
 	__raw_writel(0xAAAA, base + OMAP_WDT_SPR);
 	while (__raw_readl(base + OMAP_WDT_WPS) & 0x10)
@@ -58,11 +49,6 @@ int omap2_wd_timer_disable(struct omap_hwmod *oh)
 	while (__raw_readl(base + OMAP_WDT_WPS) & 0x10)
 		cpu_relax();
 
-	ret = omap_hwmod_idle(oh);
-	if (ret)
-		pr_err("%s: Could not disable clocks for %s\n",
-				oh->name, __func__);
-
-	return ret;
+	return 0;
 }