linux-kernel - Re: [PATCH] ARM: at91: pm: cpu_idle: switch DDR to power-down mode

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Date:   Mon, 13 Mar 2017 22:07:42 +0100
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Nicolas Ferre <nicolas.ferre@...rochip.com>
Cc:     Boris BREZILLON <boris.brezillon@...e-electrons.com>,
        Wenyou Yang <wenyou.yang@...rochip.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: at91: pm: cpu_idle: switch DDR to power-down mode

On 13/03/2017 at 18:14:50 +0100, Nicolas Ferre wrote:
> On some DDR controllers, compatible with the sama5d3 one,
> the sequence to enter/exit/re-enter the self-refresh mode adds
> more constrains than what is currently written in the at91_idle
> driver. An actual access to the DDR chip is needed between exit
> and re-enter of this mode which is somehow difficult to implement.
> This sequence can completely hang the SoC. It is particularly
> experienced on parts which embed a L2 cache if the code run
> between IDLE calls fits in it...
> 
> Moreover, as the intention is to enter and exit pretty rapidly
> from IDLE, the power-down mode is a good candidate.
> 
> So now we use power-down instead of self-refresh. As we can
> simplify the funciton for sama5d3 compatible DDR controllers,
              typo ^

> we instanciate a new sama5d3_ddr_standby() function.
> 
> Signed-off-by: Nicolas Ferre <nicolas.ferre@...rochip.com>
> ---
>  arch/arm/mach-at91/pm.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mach-at91/pm.c b/arch/arm/mach-at91/pm.c
> index 3d89b7905bd9..63e7df8ec815 100644
> --- a/arch/arm/mach-at91/pm.c
> +++ b/arch/arm/mach-at91/pm.c
> @@ -289,6 +289,23 @@ static void at91_ddr_standby(void)
>  		at91_ramc_write(1, AT91_DDRSDRC_LPR, saved_lpr1);
>  }
>  
> +static void sama5d3_ddr_standby(void)
> +{
> +	u32 lpr0;
> +	u32 saved_lpr0;
> +
> +	saved_lpr0 = at91_ramc_read(0, AT91_DDRSDRC_LPR);
> +	lpr0 = saved_lpr0 & ~AT91_DDRSDRC_LPCB;
> +	lpr0 |= AT91_DDRSDRC_LPCB_POWER_DOWN;
> +
> +	/* self-refresh mode now */

So this is not self refresh anymore


-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com