RE: [PATCH v2 07/12] mmc: sd: set current limit for uhs cards

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Hi Philip,


> -----Original Message-----
> From: Philip Rakity [mailto:prakity@xxxxxxxxxxx]
> Sent: Wednesday, March 16, 2011 7:56 PM
> To: Nath, Arindam
> Cc: cjb@xxxxxxxxxx; zhangfei.gao@xxxxxxxxx; subhashj@xxxxxxxxxxxxxx;
> linux-mmc@xxxxxxxxxxxxxxx; Su, Henry; Lu, Aaron; anath.amd@xxxxxxxxx
> Subject: Re: [PATCH v2 07/12] mmc: sd: set current limit for uhs cards
> 
> 
> On Mar 4, 2011, at 3:32 AM, Arindam Nath wrote:
> 
> > We decide on the current limit to be set for the card based on the
> > Capability of Host Controller to provide current at 1.8V signalling,
> > and the maximum current limit of the card as indicated by CMD6
> > mode 0. We then set the current limit for the card using CMD6 mode 1.
> >
> > Signed-off-by: Arindam Nath <arindam.nath@xxxxxxx>
> > ---
> > drivers/mmc/core/sd.c    |   45
> +++++++++++++++++++++++++++++++++++++++++++++
> > drivers/mmc/host/sdhci.c |   24 ++++++++++++++++++++++++
> > include/linux/mmc/card.h |    9 +++++++++
> > include/linux/mmc/host.h |    1 +
> > 4 files changed, 79 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
> > index ec0d8e6..df98a2c 100644
> > --- a/drivers/mmc/core/sd.c
> > +++ b/drivers/mmc/core/sd.c
> > @@ -550,6 +550,46 @@ static int sd_set_bus_speed_mode(struct mmc_card
> *card, u8 *status)
> > 	return 0;
> > }
> >
> > +static int sd_set_current_limit(struct mmc_card *card, u8 *status)
> > +{
> > +	struct mmc_host *host = card->host;
> > +	int mmc_host_max_current_180, current_limit;
> > +	int err;
> > +
> > +	/* sanity check */
> > +	if (!host->ops->get_max_current_180)
> > +		return 0;
> 
> a better name would be get_max_current rather than get_max_current_180

The Max Current Capabilities register reports maximum currents for 1.8V, 3.0V and 3.3V. Since we are only interested in the maximum current at 1.8V, so I have added *_180 to the variable names to make it explicit.

> 
> do you want a test for get_max_current_180 < 400 ? and return 0  have
> it do the switch
> by setting the value ?

As mentioned in the Physical Layer spec v3.01, <400mA falls under the default current limit, so we don't need to set it in case any or all of the above conditions fail.

Thanks,
Arindam

> > +
> > +	/* Maximum current supported by host at 1.8V */
> > +	mmc_host_max_current_180 = host->ops->get_max_current_180(host);
> > +
> > +	if (mmc_host_max_current_180 >= 800) {
> > +		if (card->sw_caps.uhs_curr_limit & SD_MAX_CURRENT_800)
> > +			current_limit = SD_SET_CURRENT_LIMIT_800;
> > +		else if (card->sw_caps.uhs_curr_limit & SD_MAX_CURRENT_600)
> > +			current_limit = SD_SET_CURRENT_LIMIT_600;
> > +		else if (card->sw_caps.uhs_curr_limit & SD_MAX_CURRENT_400)
> > +			current_limit = SD_SET_CURRENT_LIMIT_400;
> > +	} else if (mmc_host_max_current_180 >= 600) {
> > +		if (card->sw_caps.uhs_curr_limit & SD_MAX_CURRENT_600)
> > +			current_limit = SD_SET_CURRENT_LIMIT_600;
> > +		else if (card->sw_caps.uhs_curr_limit & SD_MAX_CURRENT_400)
> > +			current_limit = SD_SET_CURRENT_LIMIT_400;
> > +	} else if (mmc_host_max_current_180 >= 400)
> > +		if (card->sw_caps.uhs_curr_limit & SD_MAX_CURRENT_400)
> > +			current_limit = SD_SET_CURRENT_LIMIT_400;
> 
> or
>         else
>                current_limit = SD_SET_CURRENT_LIMIT_200;
> > +
> > +	err = mmc_sd_switch(card, 1, 3, current_limit, status);
> > +	if (err)
> > +		return err;
> > +
> > +	if (((status[15] >> 4) & 0x0F) != current_limit)
> > +		printk(KERN_WARNING "%s: Problem setting current limit!\n",
> > +			mmc_hostname(card->host));
> > +
> > +	return 0;
> > +}
> > +
> > /*
> >  * UHS-I specific initialization procedure
> >  */
> > @@ -590,6 +630,11 @@ static int mmc_sd_init_uhs_card(struct mmc_card
> *card)
> >
> > 	/* Set bus speed mode of the card */
> > 	err = sd_set_bus_speed_mode(card, status);
> > +	if (err)
> > +		goto out;
> > +
> > +	/* Set current limit for the card */
> > +	err = sd_set_current_limit(card, status);
> >
> > out:
> > 	kfree(status);
> > diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > index f127fa2..245cc39 100644
> > --- a/drivers/mmc/host/sdhci.c
> > +++ b/drivers/mmc/host/sdhci.c
> > @@ -1462,12 +1462,36 @@ static int
> sdhci_start_signal_voltage_switch(struct mmc_host *mmc)
> > 	return -EAGAIN;
> > }
> >
> 
> better name is sdhci_get_max_current
> 
> > +static int sdhci_get_max_current_180(struct mmc_host *mmc)
> > +{
> > +	struct sdhci_host *host;
> > +	u32 max_current_caps;
> > +	unsigned long flags;
> > +	int max_current_180;
> > +
> > +	host = mmc_priv(mmc);
> > +
> > +	spin_lock_irqsave(&host->lock, flags);
> > +
> > +	max_current_caps = sdhci_readl(host, SDHCI_MAX_CURRENT);
> > +
> > +	spin_unlock_irqrestore(&host->lock, flags);
> > +
> > +	/* Maximum current is 4 times the register value for 1.8V */
> > +	max_current_180 = ((max_current_caps &
> SDHCI_MAX_CURRENT_180_MASK) >>
> > +			   SDHCI_MAX_CURRENT_180_SHIFT) *
> > +			   SDHCI_MAX_CURRENT_MULTIPLIER;
> 
>  SDHCI_MAX_CURRENT_SHIFT is better name.
> 
> > +
> > +	return max_current_180;
> > +}
> > +
> > static const struct mmc_host_ops sdhci_ops = {
> > 	.request	= sdhci_request,
> > 	.set_ios	= sdhci_set_ios,
> > 	.get_ro		= sdhci_get_ro,
> > 	.enable_sdio_irq = sdhci_enable_sdio_irq,
> > 	.start_signal_voltage_switch	=
> sdhci_start_signal_voltage_switch,
> > +	.get_max_current_180		= sdhci_get_max_current_180,
> 
> .get_max_current = sdhci_get_max_current;
> > };
> >
> >
> /**********************************************************************
> *******\
> > diff --git a/include/linux/mmc/card.h b/include/linux/mmc/card.h
> > index 0b24c41..a6811ae 100644
> > --- a/include/linux/mmc/card.h
> > +++ b/include/linux/mmc/card.h
> > @@ -98,6 +98,15 @@ struct sd_switch_caps {
> > #define SD_DRIVER_TYPE_C	0x04
> > #define SD_DRIVER_TYPE_D	0x08
> > 	unsigned int		uhs_curr_limit;
> > +#define SD_SET_CURRENT_LIMIT_200	0
> > +#define SD_SET_CURRENT_LIMIT_400	1
> > +#define SD_SET_CURRENT_LIMIT_600	2
> > +#define SD_SET_CURRENT_LIMIT_800	3
> > +
> > +#define SD_MAX_CURRENT_200	(1 << SD_SET_CURRENT_LIMIT_200)
> > +#define SD_MAX_CURRENT_400	(1 << SD_SET_CURRENT_LIMIT_400)
> > +#define SD_MAX_CURRENT_600	(1 << SD_SET_CURRENT_LIMIT_600)
> > +#define SD_MAX_CURRENT_800	(1 << SD_SET_CURRENT_LIMIT_800)
> > };
> >
> > struct sdio_cccr {
> > diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> > index 4dfff6d..e84cd05 100644
> > --- a/include/linux/mmc/host.h
> > +++ b/include/linux/mmc/host.h
> > @@ -128,6 +128,7 @@ struct mmc_host_ops {
> > 	void	(*init_card)(struct mmc_host *host, struct mmc_card *card);
> >
> > 	int	(*start_signal_voltage_switch)(struct mmc_host *host);
> > +	int	(*get_max_current_180)(struct mmc_host *mmc);
> > };
> >
> > struct mmc_card;
> > --
> > 1.7.1
> >
> 


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