ARM: imx: improve the comment of CCM lpm SW workaround

Improve the comment of SW workaround for CCM lpm issue using
hardware errata description to avoid confusion.

ERR007265: CCM: When improper low-power sequence is used, the SoC
enters low power mode before the ARM core executes WFI.

Software workaround:
1) Software should trigger IRQ torvalds#32 (IOMUX) to be always pending
   by setting IOMUX_GPR1_GINT.
2) Software should then unmask IRQ torvalds#32 in GPC before setting CCM
   Low-Power mode.
3) Software should mask IRQ torvalds#32 right after CCM Low-Power mode is
   set (set bits 0-1 of CCM_CLPCR).

Signed-off-by: Anson Huang <[email protected]>
Signed-off-by: Shawn Guo <[email protected]>

Author: Anson Huang

arch/arm/mach-imx/pm-imx6q.c

@@ -156,10 +156,16 @@ int imx6q_set_lpm(enum mxc_cpu_pwr_mode mode)
 	}
 
 	/*
-	 * Unmask the always pending IOMUXC interrupt #32 as wakeup source to
-	 * deassert dsm_request signal, so that we can ensure dsm_request
-	 * is not asserted when we're going to write CLPCR register to set LPM.
-	 * After setting up LPM bits, we need to mask this wakeup source.
+	 * ERR007265: CCM: When improper low-power sequence is used,
+	 * the SoC enters low power mode before the ARM core executes WFI.
+	 *
+	 * Software workaround:
+	 * 1) Software should trigger IRQ #32 (IOMUX) to be always pending
+	 *    by setting IOMUX_GPR1_GINT.
+	 * 2) Software should then unmask IRQ #32 in GPC before setting CCM
+	 *    Low-Power mode.
+	 * 3) Software should mask IRQ #32 right after CCM Low-Power mode
+	 *    is set (set bits 0-1 of CCM_CLPCR).
 	 */
 	iomuxc_irq_desc = irq_to_desc(32);
 	imx_gpc_irq_unmask(&iomuxc_irq_desc->irq_data);
@@ -219,6 +225,8 @@ void __init imx6q_pm_init(void)
 	WARN_ON(!ccm_base);
 
 	/*
+	 * This is for SW workaround step #1 of ERR007265, see comments
+	 * in imx6q_set_lpm for details of this errata.
 	 * Force IOMUXC irq pending, so that the interrupt to GPC can be
 	 * used to deassert dsm_request signal when the signal gets
 	 * asserted unexpectedly.