ARM: OMAP4: PM: Warn users about usage of older bootloaders

OMAP4 CHIP level PM works only with newer bootloaders. The
dependency on the bootloader comes from the fact that the
kernel is missing reset and initialization code for some
devices.

While the right thing to do is to add reset and init code in
the kernel, for some co-processor IP blocks like DSP and IVA
it means downloading firmware into each one of them to execute
idle instructions.

While a feasible solution is worked upon on how such IP blocks
can be better handled in the kernel, in the interim, to avoid
any further frustration to users testing PM on OMAP4 and finding
it broken, warn them about the bootloader being a possible
cause.
Signed-off-by: NRajendra Nayak <rnayak@ti.com>
Cc: Tero Kristo <t-kristo@ti.com>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: R Sricharan <r.sricharan@ti.com>
[paul@pwsan.com: tweaked warning messages and comments slightly]
Acked-by: NKevin Hilman <khilman@linaro.org>
[paul@pwsan.com: fixed checkpatch warning]
Signed-off-by: NPaul Walmsley <paul@pwsan.com>

arch/arm/mach-omap2/pm44xx.c

@@ -77,10 +77,20 @@ static int omap4_pm_suspend(void)
 		omap_set_pwrdm_state(pwrst->pwrdm, pwrst->saved_state);
 		pwrdm_set_logic_retst(pwrst->pwrdm, pwrst->saved_logic_state);
 	}
-	if (ret)
+	if (ret) {
 		pr_crit("Could not enter target state in pm_suspend\n");
-	else
+		/*
+		 * OMAP4 chip PM currently works only with certain (newer)
+		 * versions of bootloaders. This is due to missing code in the
+		 * kernel to properly reset and initialize some devices.
+		 * Warn the user about the bootloader version being one of the
+		 * possible causes.
+		 * http://www.spinics.net/lists/arm-kernel/msg218641.html
+		 */
+		pr_warn("A possible cause could be an old bootloader - try u-boot >= v2012.07\n");
+	} else {
 		pr_info("Successfully put all powerdomains to target state\n");
+	}
 
 	return 0;
 }
@@ -146,6 +156,13 @@ int __init omap4_pm_init(void)
 	}
 
 	pr_err("Power Management for TI OMAP4.\n");
+	/*
+	 * OMAP4 chip PM currently works only with certain (newer)
+	 * versions of bootloaders. This is due to missing code in the
+	 * kernel to properly reset and initialize some devices.
+	 * http://www.spinics.net/lists/arm-kernel/msg218641.html
+	 */
+	pr_warn("OMAP4 PM: u-boot >= v2012.07 is required for full PM support\n");
 
 	ret = pwrdm_for_each(pwrdms_setup, NULL);
 	if (ret) {