RE: [PATCHv2 1/4] sdhci-s3c: add support for the non standard minimal clock value

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hello,

On Wednesday, July 28, 2010 6:48 PM Ben Dooks wrote:

> On 28/07/10 15:19, Marek Szyprowski wrote:
> > S3C SDHCI host controller can change the source for generating mmc clock.
> > By default host bus clock is used, what causes some problems on machines
> > with 133MHz bus, because the SDHCI divider cannot be as high get proper
> > clock value for identification mode. This is not a problem for the
> > controller, because it can generate lower frequencies from other clock
> > sources. This patch adds a new quirk to SDHCI driver to calculate the
> > minimal supported clock frequency.
> >
> > This fixes the flood of the following warnings on Samsung S5PV210 SoCs:
> > mmc0: Minimum clock frequency too high for identification mode
> >
> > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> > Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
> > ---
> >
> > Changes since V1:
> > - rebased onto latest -mm kernel tree
> >
> > ---
> >  drivers/mmc/host/sdhci-of-esdhc.c |    1 +
> >  drivers/mmc/host/sdhci-s3c.c      |   29 +++++++++++++++++++++++++++++
> >  drivers/mmc/host/sdhci.c          |    2 +-
> >  drivers/mmc/host/sdhci.h          |    2 ++
> >  4 files changed, 33 insertions(+), 1 deletions(-)
> >
> > diff --git a/drivers/mmc/host/sdhci-of-esdhc.c b/drivers/mmc/host/sdhci-
> of-esdhc.c
> > index e9f99fe..763b364 100644
> > --- a/drivers/mmc/host/sdhci-of-esdhc.c
> > +++ b/drivers/mmc/host/sdhci-of-esdhc.c
> > @@ -124,6 +124,7 @@ struct sdhci_of_data sdhci_esdhc = {
> >  		  SDHCI_QUIRK_BROKEN_CARD_DETECTION |
> >  		  SDHCI_QUIRK_NO_BUSY_IRQ |
> >  		  SDHCI_QUIRK_NONSTANDARD_CLOCK |
> > +		  SDHCI_QUIRK_NONSTANDARD_MINCLOCK |
> >  		  SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK |
> >  		  SDHCI_QUIRK_PIO_NEEDS_DELAY |
> >  		  SDHCI_QUIRK_RESTORE_IRQS_AFTER_RESET |
> > diff --git a/drivers/mmc/host/sdhci-s3c.c b/drivers/mmc/host/sdhci-s3c.c
> > index d7058ee..5218f2b 100644
> > --- a/drivers/mmc/host/sdhci-s3c.c
> > +++ b/drivers/mmc/host/sdhci-s3c.c
> > @@ -203,9 +203,36 @@ static void sdhci_s3c_set_clock(struct sdhci_host
> *host, unsigned int clock)
> >  	}
> >  }
> >
> > +/**
> > + * sdhci_s3c_get_min_clock - callback to get minimal supported clock
> value
> > + * @host: The SDHCI host being queried
> > + *
> > + * To init mmc host properly a minimal clock value is needed. For high
> system
> > + * bus clock's values the standard formula gives values out of allowed
> range.
> > + * The clock still can be set to lower values, if clock source other
> then
> > + * system bus is selected.
> > +*/
> > +static unsigned int sdhci_s3c_get_min_clock(struct sdhci_host *host)
> > +{
> > +	struct sdhci_s3c *ourhost = to_s3c(host);
> > +	unsigned int delta, min = UINT_MAX;
> > +	int src;
> > +
> > +	for (src = 0; src < MAX_BUS_CLK; src++) {
> > +		delta = sdhci_s3c_consider_clock(ourhost, src, 0);
> > +		if (delta == UINT_MAX)
> > +			continue;
> > +		/* delta is a negative value in this case */
> > +		if (-delta < min)
> > +			min = -delta;
> > +	}
> > +	return min;
> > +}
> > +
> >  static struct sdhci_ops sdhci_s3c_ops = {
> >  	.get_max_clock		= sdhci_s3c_get_max_clk,
> >  	.set_clock		= sdhci_s3c_set_clock,
> > +	.get_min_clock		= sdhci_s3c_get_min_clock,
> >  };
> >
> >  static int __devinit sdhci_s3c_probe(struct platform_device *pdev)
> > @@ -309,6 +336,8 @@ static int __devinit sdhci_s3c_probe(struct
> platform_device *pdev)
> >  	host->quirks = 0;
> >  	host->irq = irq;
> >
> > +	host->quirks |= SDHCI_QUIRK_NONSTANDARD_MINCLOCK;
> > +
> >  	/* Setup quirks for the controller */
> >  	host->quirks |= SDHCI_QUIRK_NO_ENDATTR_IN_NOPDESC;
> >
> > diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > index 07b2695..682b285 100644
> > --- a/drivers/mmc/host/sdhci.c
> > +++ b/drivers/mmc/host/sdhci.c
> > @@ -1776,7 +1776,7 @@ int sdhci_add_host(struct sdhci_host *host)
> >  	 * Set host parameters.
> >  	 */
> >  	mmc->ops = &sdhci_ops;
> > -	if (host->quirks & SDHCI_QUIRK_NONSTANDARD_CLOCK &&
> > +	if (host->quirks & SDHCI_QUIRK_NONSTANDARD_MINCLOCK &&
> >  			host->ops->get_min_clock)
> >  		mmc->f_min = host->ops->get_min_clock(host);
> 
> We're begining to run out of quirk space, given these fields will
> be initialised to NULL if not used, then why not just check for
> the op being present?

Ok, I can remove the quirk and just check if the op is present. However
having a separate quirk makes the code easier to understand (quirk shows 
that the particular implementation differs from the standard).

Best regards
--
Marek Szyprowski
Samsung Poland R&D Center