linux-kernel - [PATCH V2] ARM: imx: improve the comment of CCM lpm SW workaround

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Message-ID: <1387923561-8724-1-git-send-email-b20788@freescale.com>
Date:	Tue, 24 Dec 2013 17:19:21 -0500
From:	Anson Huang <b20788@...escale.com>
To:	<shawn.guo@...aro.org>, <kernel@...gutronix.de>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH V2] 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@...escale.com>
---
 arch/arm/mach-imx/pm-imx6q.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/arm/mach-imx/pm-imx6q.c b/arch/arm/mach-imx/pm-imx6q.c
index aecd9f8..31cb9d6 100644
--- a/arch/arm/mach-imx/pm-imx6q.c
+++ b/arch/arm/mach-imx/pm-imx6q.c
@@ -156,10 +156,13 @@ 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 +222,8 @@ 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.
-- 
1.7.9.5


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