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

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Date:	Tue, 24 Dec 2013 21:54:44 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Anson Huang <b20788@...escale.com>
CC:	<kernel@...gutronix.de>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] ARM: imx: improve the comment of CCM lpm SW workaround

On Tue, Dec 24, 2013 at 05:19:21PM -0500, Anson Huang wrote:
> 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).

The lines are too long.  I wrapped them a little bit, and applied the
patch.

Shawn

>  	 */
>  	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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