linux-kernel - Re: [PATCH 01/14] memory: ti-emif-sram: Add resume function to recopy sram code

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Date:   Thu, 12 Apr 2018 10:44:10 -0600
From:   "santosh.shilimkar@...cle.com" <santosh.shilimkar@...cle.com>
To:     Keerthy <j-keerthy@...com>, linus.walleij@...aro.org,
        grygorii.strashko@...com, tony@...mide.com
Cc:     t-kristo@...com, Russ.Dill@...com, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org, ssantosh@...nel.org,
        haojian.zhuang@...aro.org, linux-arm-kernel@...ts.infradead.org,
        d-gerlach@...com
Subject: Re: [PATCH 01/14] memory: ti-emif-sram: Add resume function to recopy
 sram code

On 4/11/18 9:53 PM, Keerthy wrote:
> From: Dave Gerlach <d-gerlach@...com>
> 
> After an RTC+DDR cycle we lose sram context so emif pm functions present
> in sram are lost. We can check if the first byte of the original
> code in DDR contains the same first byte as the code in sram, and if
> they do not match we know we have lost context and must recopy the
> functions to the previous address to maintain PM functionality.
> 
> Signed-off-by: Dave Gerlach <d-gerlach@...com>
> Signed-off-by: Keerthy <j-keerthy@...com>
> ---
>   drivers/memory/ti-emif-pm.c | 24 ++++++++++++++++++++++++
>   1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/memory/ti-emif-pm.c b/drivers/memory/ti-emif-pm.c
> index 632651f..ec4a62c 100644
> --- a/drivers/memory/ti-emif-pm.c
> +++ b/drivers/memory/ti-emif-pm.c
> @@ -249,6 +249,25 @@ int ti_emif_get_mem_type(void)
>   };
>   MODULE_DEVICE_TABLE(of, ti_emif_of_match);
>   
> +#ifdef CONFIG_PM_SLEEP
> +static int ti_emif_resume(struct device *dev)
> +{
> +	unsigned long tmp =
> +			__raw_readl((void *)emif_instance->ti_emif_sram_virt);
> +
> +	/*
> +	 * Check to see if what we are copying is already present in the
> +	 * first byte at the destination, only copy if it is not which
> +	 * indicates we have lost context and sram no longer contains
> +	 * the PM code
> +	 */

> +	if (tmp != ti_emif_sram)
> +		ti_emif_push_sram(dev, emif_instance);
> +
> +	return 0;
> +}
> +#endif /* CONFIG_PM_SLEEP */
Instead of this indirect method , why can't just check the previous
deep sleep mode and based on that do copy or not. EMIF power status
register should have something like that ?

Another minor point is even though there is nothing to do in suspend,
might be good to have a callback with comment that nothing to do with
some explanation why not. Don't have strong preference but may for
better readability.

Regards,
Santosh