linux-kernel - RE: [PATCH RFC] mmc : omap_hsmmc : Save and restore the sysc across reset

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Date:	Mon, 16 Jan 2012 13:11:46 +0000
From:	<ext-denis.2.karpov@...ia.com>
To:	<shubhrajyoti@...com>, <linux-mmc@...r.kernel.org>
CC:	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH RFC] mmc : omap_hsmmc : Save and restore the sysc across
 reset

ext Shubhrajyoti D wrote on 2012-01-16:
> The commit 11dd62:[omap_hsmmc: context save/restore support]
> 
> does a reset and restores AUTOIDLE settings.
> This patch saves the register does a reset and restores
> the same configuration.
...
>  	if (pdata->get_context_loss_count) {
> @@ -700,6 +700,7 @@ static int omap_hsmmc_context_restore(struct omap_hsmmc_host
> *host)
>  		&& time_before(jiffies, timeout))
>  		;
> +	sysc = OMAP_HSMMC_READ(host->base, SYSCONFIG);
>  	/* Do software reset */
>  	OMAP_HSMMC_WRITE(host->base, SYSCONFIG, SOFTRESET);
>  	timeout = jiffies + msecs_to_jiffies(MMC_TIMEOUT_MS);
> @@ -707,8 +708,7 @@ static int omap_hsmmc_context_restore(struct omap_hsmmc_host
> *host)
>  		&& time_before(jiffies, timeout))
>  		;
> -	OMAP_HSMMC_WRITE(host->base, SYSCONFIG,
> -			OMAP_HSMMC_READ(host->base, SYSCONFIG) | AUTOIDLE);
> +	OMAP_HSMMC_WRITE(host->base, SYSCONFIG, sysc);

The meaning of the code is to restore the register context after it was lost during transition into low power consumption state. SW reset is needed to bring all the registers in a consistent state before reconfiguring some of them. 

Saving and restoring the SYSCONFIG register across SW reset is not needed. 

Also re-configuring AUTOIDLE feature is not necessary since SYSCONFIG reset value has is 1 already, according to TRM. I guess it was done to make things more explicit.

Denis
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