RE: [PATCH v2 3/5] mmc: dw_mmc: Add exynos resume_noirq callback to clear WAKEUP_INT

[Seungwon Jeon <tgih.jun@samsung.com>]

On Thu, July 11, 2013, Doug Anderson wrote:
> Seungwon,
> 
> On Wed, Jul 10, 2013 at 7:54 AM, Seungwon Jeon <tgih.jun@samsung.com> wrote:
> > On Wed, July 10, 2013, Doug Anderson wrote:
> >> If the WAKEUP_INT is asserted at wakeup and not cleared, we'll end up
> >> looping around forever.  This has been seen to happen on exynos5420
> >> silicon despite the fact that we haven't enabled any wakeup events.
> >>
> >> Signed-off-by: Doug Anderson <dianders@chromium.org>
> >> ---
> >> Changes in v2:
> >> - Use suspend_noirq as per James Hogan.
> >>
> >>  drivers/mmc/host/dw_mmc-exynos.c | 23 +++++++++++++++++++++++
> >>  1 file changed, 23 insertions(+)
> >>
> >> diff --git a/drivers/mmc/host/dw_mmc-exynos.c b/drivers/mmc/host/dw_mmc-exynos.c
> >> index f013e7e..36b9620 100644
> >> --- a/drivers/mmc/host/dw_mmc-exynos.c
> >> +++ b/drivers/mmc/host/dw_mmc-exynos.c
> >> @@ -30,6 +30,7 @@
> >>  #define SDMMC_CLKSEL_TIMING(x, y, z) (SDMMC_CLKSEL_CCLK_SAMPLE(x) |  \
> >>                                       SDMMC_CLKSEL_CCLK_DRIVE(y) |    \
> >>                                       SDMMC_CLKSEL_CCLK_DIVIDER(z))
> >> +#define SDMMC_CLKSEL_WAKEUP_INT              BIT(11)
> >>
> >>  #define SDMMC_CMD_USE_HOLD_REG               BIT(29)
> >>
> >> @@ -102,6 +103,27 @@ static int dw_mci_exynos_setup_clock(struct dw_mci *host)
> >>       return 0;
> >>  }
> >>
> >> +/**
> >> + * dw_mci_exynos_resume_noirq - Exynos-specific resume code
> >> + *
> >> + * We have seen cases (at least on the exynos5420) where turning off the INT
> >> + * power rail during suspend will leave the WAKEUP_INT bit in the CLKSEL
> >> + * register asserted.  This bit is 1 to indicate that it fired and we can
> >> + * clear it by writing a 1 back.  Clear it to prevent interrupts from going off
> >> + * constantly.
> >> + */
> > As I know this bit is auto-cleared.
> > Did you find the cause of this problem?
> > How about your GPIO setting in sleep?
> > Currently, we don't know why the problem is happened.
> > At least, we should make it clear.
> 
> Yes, the documentation that I have says that this bit is "auto
> cleared" as well but doesn't indicate under what conditions it is auto
> cleared.  From testing how this bit reacts I have found that writing a
> 1 to it clears the bit--in other words it behaves like bits in
> RINTSTS.  That's a terrible design for a bit in a register with shared
> config but appears to be how it works.
> 
> Note: in a sense it will be "auto cleared" because doing a
> read-modify-write of any other bits in this register will clear the
> interrupt.
> 
> I have asked for official confirmation.
> 
> We have found that on exynos5420 bits 8-10 of CLKSEL are marked as
> RESERVED.  Those bits are documented to enable the WAKEUP_INT on
> exynos5250.  My best guess is that these bits are not used on
> exynos5420 and the WAKEUP_INT line is left floating, which means it
> can fire randomly.  I have also asked for official confirmation about
> this.
Sorry for late response.
Yes, it's not clear.
If you get the confirmation, could you share this problem?
Possibly, auto-clear may not be implemented.
Then, manual should be correct.

Thanks,
Seungwon Jeon
> 
> 
> I will likely merge this change locally in our kernel tree while
> waiting for a response.  If you would like to wait before Acking
> that's very reasonable.  Do you have any other problems with this
> change assuming my understanding above is correct?
> 
> -Doug
> --
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