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 #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).

Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

1 files changed, 12 insertions, 4 deletions

diff --git a/arch/arm/mach-imx/pm-imx6q.c b/arch/arm/mach-imx/pm-imx6q.c
index aecd9f8037e0..9d47adc078aa 100644
--- a/arch/arm/mach-imx/pm-imx6q.c
+++ b/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.