Re: [PATCH] mmc: core: Wait for Vdd to settle on card power off
From: Kyle Roeschley
Date: Fri Sep 22 2017 - 10:09:46 EST
On Fri, Sep 22, 2017 at 11:38:40AM +0200, Ulf Hansson wrote:
> On 21 September 2017 at 19:47, Kyle Roeschley <kyle.roeschley@xxxxxx> wrote:
> > The SD spec version 6.0 section 220.127.116.11 requires that Vdd must be
> > lowered to less than 0.5V for a minimum of 1 ms when powering off a
> > card. Increase our wait to 10 ms so that voltage has time to drain down
> > to 0.5V and cards can power off correctly.
> > Signed-off-by: Kyle Roeschley <kyle.roeschley@xxxxxx>
> > ---
> > drivers/mmc/core/core.c | 10 ++++------
> > 1 file changed, 4 insertions(+), 6 deletions(-)
> > diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> > index 66c9cf49ad2f..38630246de26 100644
> > --- a/drivers/mmc/core/core.c
> > +++ b/drivers/mmc/core/core.c
> > @@ -1679,18 +1679,16 @@ void mmc_power_off(struct mmc_host *host)
> > mmc_set_initial_state(host);
> > /*
> > - * Some configurations, such as the 802.11 SDIO card in the OLPC
> > - * XO-1.5, require a short delay after poweroff before the card
> > - * can be successfully turned on again.
> > + * The SD spec requires at least 1 ms with Vdd at less than 0.5 V
> > + * before a card can be re-powered, but we need to wait longer so that
> > + * the voltage has time to drain.
> > */
> > - mmc_delay(1);
> > + mmc_delay(10);
> No, this isn't the proper place of adding more "magic" delays.
> Instead, make sure the related ->set_ios() callback in the mmc host
> driver deals with this instead. In case it uses an external regulator,
> via the regulator API, then this is something that should be
> controlled with the definition of the regulator.
Thanks for pointing me in the right direction, I'll reimplement the fix there.