[PATCH 4/4] mmc: dw_mmc: correct the calculation for CLKDIV

[PATCH 4/4] mmc: dw_mmc: correct the calculation for CLKDIV

[Seungwon Jeon]

In case of "host->bus_hz < slot->clock", divider value is
miscalculated. And clock divider register value is multiple
of 2. If calculated divider value is odd number, result can
be over-clocking.

Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
---
 drivers/mmc/host/dw_mmc.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index f2f8463..c87745e 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -617,14 +617,16 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot)
 	u32 div;
 
 	if (slot->clock != host->current_speed) {
-		if (host->bus_hz % slot->clock)
+		div = host->bus_hz / slot->clock;
+		if (host->bus_hz % slot->clock &&
+			host->bus_hz > slot->clock)
 			/*
 			 * move the + 1 after the divide to prevent
 			 * over-clocking the card.
 			 */
-			div = ((host->bus_hz / slot->clock) >> 1) + 1;
-		else
-			div = (host->bus_hz  / slot->clock) >> 1;
+			div += 1;
+
+		div = (host->bus_hz != slot->clock) ? DIV_ROUND_UP(div, 2) : 0;
 
 		dev_info(&slot->mmc->class_dev,
 			 "Bus speed (slot %d) = %dHz (slot req %dHz, actual %dHZ"
-- 
1.7.0.4

Re: [PATCH 4/4] mmc: dw_mmc: correct the calculation for CLKDIV

[Will Newton]

On Sun, May 20, 2012 at 5:27 AM, Seungwon Jeon <tgih.jun@samsung.com> wrote:
> In case of "host->bus_hz < slot->clock", divider value is
> miscalculated. And clock divider register value is multiple
> of 2. If calculated divider value is odd number, result can
> be over-clocking.
>
> Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
> ---
>  drivers/mmc/host/dw_mmc.c |   10 ++++++----
>  1 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index f2f8463..c87745e 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -617,14 +617,16 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot)
>        u32 div;
>
>        if (slot->clock != host->current_speed) {
> -               if (host->bus_hz % slot->clock)
> +               div = host->bus_hz / slot->clock;
> +               if (host->bus_hz % slot->clock &&
> +                       host->bus_hz > slot->clock)
>                        /*
>                         * move the + 1 after the divide to prevent
>                         * over-clocking the card.
>                         */

This comment seems to be no longer relevant so it should be removed.

> -                       div = ((host->bus_hz / slot->clock) >> 1) + 1;
> -               else
> -                       div = (host->bus_hz  / slot->clock) >> 1;
> +                       div += 1;
> +
> +               div = (host->bus_hz != slot->clock) ? DIV_ROUND_UP(div, 2) : 0;
>
>                dev_info(&slot->mmc->class_dev,
>                         "Bus speed (slot %d) = %dHz (slot req %dHz, actual %dHZ"
> --
> 1.7.0.4
>
>
> --
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RE: [PATCH 4/4] mmc: dw_mmc: correct the calculation for CLKDIV

[Seungwon Jeon]

Will Newton <will.newton@gmail.com> wrote:
> On Sun, May 20, 2012 at 5:27 AM, Seungwon Jeon <tgih.jun@samsung.com> wrote:
> > In case of "host->bus_hz < slot->clock", divider value is
> > miscalculated. And clock divider register value is multiple
> > of 2. If calculated divider value is odd number, result can
> > be over-clocking.
> >
> > Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
> > ---
> >  drivers/mmc/host/dw_mmc.c |   10 ++++++----
> >  1 files changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> > index f2f8463..c87745e 100644
> > --- a/drivers/mmc/host/dw_mmc.c
> > +++ b/drivers/mmc/host/dw_mmc.c
> > @@ -617,14 +617,16 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot)
> >        u32 div;
> >
> >        if (slot->clock != host->current_speed) {
> > -               if (host->bus_hz % slot->clock)
> > +               div = host->bus_hz / slot->clock;
> > +               if (host->bus_hz % slot->clock &&
> > +                       host->bus_hz > slot->clock)
> >                        /*
> >                         * move the + 1 after the divide to prevent
> >                         * over-clocking the card.
> >                         */
> 
> This comment seems to be no longer relevant so it should be removed.
> 
> > -                       div = ((host->bus_hz / slot->clock) >> 1) + 1;
> > -               else
> > -                       div = (host->bus_hz  / slot->clock) >> 1;
> > +                       div += 1;
div += 1;
It's still effective.

Best regards,
Seungwon Jeon
> > +
> > +               div = (host->bus_hz != slot->clock) ? DIV_ROUND_UP(div, 2) : 0;
> >
> >                dev_info(&slot->mmc->class_dev,
> >                         "Bus speed (slot %d) = %dHz (slot req %dHz, actual %dHZ"
> > --
> > 1.7.0.4
> >
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-mmc" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> --
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