RE: [PATCH V2 13/32] omap_hsmmc: context save/restore support

["Madhusudhan" <madhu.cr@ti.com>]

> -----Original Message-----
> From: Adrian Hunter [mailto:adrian.hunter@nokia.com]
> Sent: Thursday, July 30, 2009 2:40 AM
> To: Madhusudhan
> Cc: 'Andrew Morton'; Lavinen Jarkko (Nokia-D/Helsinki); 'linux-omap
> Mailing List'; 'Pierre Ossman'; Karpov Denis.2 (EXT-Teleca/Helsinki);
> 'Matt Fleming'; 'lkml'
> Subject: Re: [PATCH V2 13/32] omap_hsmmc: context save/restore support
> 
> Madhusudhan wrote:
> >
> >> -----Original Message-----
> >> From: linux-omap-owner@vger.kernel.org [mailto:linux-omap-
> >> owner@vger.kernel.org] On Behalf Of Adrian Hunter
> >> Sent: Tuesday, July 28, 2009 5:40 AM
> >> To: Andrew Morton
> >> Cc: Jarkko Lavinen; Adrian Hunter; linux-omap Mailing List; Pierre
> Ossman;
> >> Denis Karpov; Matt Fleming; lkml
> >> Subject: [PATCH V2 13/32] omap_hsmmc: context save/restore support
> >>
> >> From 43e9fa346d7e386328876a8535dc8619bd1f47ae Mon Sep 17 00:00:00 2001
> >> From: Denis Karpov <ext-denis.2.karpov@nokia.com>
> >> Date: Wed, 22 Apr 2009 16:04:25 +0200
> >> Subject: [PATCH] omap_hsmmc: context save/restore support
> >>
> >> Keep the context over PM dynamic OFF states.
> >>
> >> Signed-off-by: Denis Karpov <ext-denis.2.karpov@nokia.com>
> >> Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
> >> ---
> >>  drivers/mmc/host/omap_hsmmc.c |  194
> >> ++++++++++++++++++++++++++++++++++++++--
> >>  1 files changed, 184 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/drivers/mmc/host/omap_hsmmc.c
> b/drivers/mmc/host/omap_hsmmc.c
> >> index c28d055..ac1a3bf 100644
> >> --- a/drivers/mmc/host/omap_hsmmc.c
> >> +++ b/drivers/mmc/host/omap_hsmmc.c
> >> @@ -37,6 +37,7 @@
> >>
> >>  /* OMAP HSMMC Host Controller Registers */
> >>  #define OMAP_HSMMC_SYSCONFIG	0x0010
> >> +#define OMAP_HSMMC_SYSSTATUS	0x0014
> >>  #define OMAP_HSMMC_CON		0x002C
> >>  #define OMAP_HSMMC_BLK		0x0104
> >>  #define OMAP_HSMMC_ARG		0x0108
> >> @@ -94,6 +95,8 @@
> >>  #define DUAL_VOLT_OCR_BIT	7
> >>  #define SRC			(1 << 25)
> >>  #define SRD			(1 << 26)
> >> +#define SOFTRESET		(1 << 1)
> >> +#define RESETDONE		(1 << 0)
> >>
> >>  /*
> >>   * FIXME: Most likely all the data using these _DEVID defines should
> come
> >> @@ -152,6 +155,8 @@ struct mmc_omap_host {
> >>  	int			slot_id;
> >>  	int			dbclk_enabled;
> >>  	int			response_busy;
> >> +	int			context_loss;
> >> +
> >>  	struct	omap_mmc_platform_data	*pdata;
> >>  };
> >>
> >> @@ -166,6 +171,166 @@ static void omap_mmc_stop_clock(struct
> mmc_omap_host
> >> *host)
> >>  		dev_dbg(mmc_dev(host->mmc), "MMC Clock is not stoped\n");
> >>  }
> >>
> >> +#ifdef CONFIG_PM
> >> +
> >> +/*
> >> + * Restore the MMC host context, if it was lost as result of a
> >> + * power state change.
> >> + */
> >> +static int omap_mmc_restore_ctx(struct mmc_omap_host *host)
> >> +{
> >> +	struct mmc_ios *ios = &host->mmc->ios;
> >> +	struct omap_mmc_platform_data *pdata = host->pdata;
> >> +	int context_loss = 0;
> >> +	u32 hctl, capa, con;
> >> +	u16 dsor = 0;
> >> +	unsigned long timeout;
> >> +
> >> +	if (pdata->get_context_loss_count) {
> >> +		context_loss = pdata->get_context_loss_count(host->dev);
> >> +		if (context_loss < 0)
> >> +			return 1;
> >> +	}
> > This seems to restore the context always. The context should be restored
> > only if the card was powered OFF, Right?
> 
> Not exactly. The "context" is just the host controller registers, which
> get
> lost if power management decides to power off the host controller, which
> it
> will if it decides it is not doing anything.  For us, switching off the
> functional clock lets PM power off the host controller.  The card can be
> in
> any power state: on, off, card/regulator sleep.
> 
> The context is restored only when it has been lost - see the following
> lines.  But this is done from the "enable" method, so this is only called
> if someone is trying to access the card.
> 
> +	dev_dbg(mmc_dev(host->mmc), "context was %slost\n",
> +		context_loss == host->context_loss ? "not " : "");
> +	if (host->context_loss == context_loss)
> +		return 1;
> 
> And then further down, we skip some things if the card is off:
> 
> +	/* Do not initialize card-specific things if the power is off */
> +	if (host->power_mode == MMC_POWER_OFF)
> +		goto out;
> 
> 
> > The context could also be lost if the CORE transitions to OFF. I assume
> that
> > case gets handled here without anything extra required if "power_saving"
> is
> > set to true. Am I right?
> 
> Yes, "power_saving" is not related to "Power Management".  "power_saving"
> is about controlling the power regulators, which the host controller does
> itself without any support from PM.
> 
> To put it another way, "power_saving" and CONFIG_PM can be set
> independently
> of one another.

But the "omap_hsmmc_context_save" and " omap_hsmmc_context_restore" are
under CONFIG_PM. They are empty functions if CONFIG_PM is not set. Does this
mean that if CONFIG_PM is not set the host regulators are not turned OFF
even if there is no activity on MMC?

> 
> > How about the case of eMMC? Since it is not a removable device the card
> is
> > not powered OFF. But the CORE OFF would result in context loss. Do we
> hit
> > the restore_ctx path in that case?
> 
> On the contrary, eMMC *is* powered off.  After 100ms of inactivity, eMMC
> is
> put to card sleep, and the regulator is put to sleep also - in fact there
> are two regulators and one is powered off here.  After 8 seconds
> the other regulator is powered off and consequently after that the eMMC
> must
> be reinitialised (rescanned) before it can be used.