Re: [PATCH v2 3/3] mmc: core: Add power-off-delay-us support

[Judith Mendez]

Hi Ulf,

On 7/27/26 10:16 AM, Ulf Hansson wrote:
> On Wed, Jul 22, 2026 at 10:57 PM Judith Mendez <jm@xxxxxx> wrote:
> > Add support for power-off-delay-us which shall be used to specify
> > value of delay after deasserting power during MMC power cycles.
> > Default for delay is 1000us but custom delay can be passed in to work
> > around hardware issues such as slow RC discharge on MMC VDD rails.
> >
> > Signed-off-by: Judith Mendez <jm@xxxxxx>
> > ---
> > Changes since v1:
> > - Move delay to mmc_power_off
> > - Fix dt checks and remove print
> > - Move from mmc_host struct to mmc_ios struct
> > - Rename post-power-off-delay-ms to power_off_delay_us
> > ---
> >   drivers/mmc/core/core.c  | 2 +-
> >   drivers/mmc/core/host.c  | 8 ++++++++
> >   include/linux/mmc/host.h | 1 +
> >   3 files changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> > index 29e80e5f928e9..9472041fe1c20 100644
> > --- a/drivers/mmc/core/core.c
> > +++ b/drivers/mmc/core/core.c
> > @@ -1388,7 +1388,7 @@ void mmc_power_off(struct mmc_host *host)
> >           * XO-1.5, require a short delay after poweroff before the card
> >           * can be successfully turned on again.
> >           */
> > -       mmc_delay(1);
> > +       mmc_delay_us(host->ios.power_off_delay_us);
> >   }
> >
> >   void mmc_power_cycle(struct mmc_host *host, u32 ocr)
> > diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> > index b7ce3137d4529..fac50a2860211 100644
> > --- a/drivers/mmc/core/host.c
> > +++ b/drivers/mmc/core/host.c
> > @@ -421,6 +421,13 @@ int mmc_of_parse(struct mmc_host *host)
> >          device_property_read_u32(dev, "post-power-on-delay-ms",
> >                                   &host->ios.power_delay_ms);
> >
> > +       device_property_read_u32(dev, "power-off-delay-us",
> > +                                &host->ios.power_off_delay_us);
> > +       if (host->ios.power_off_delay_us < 1)
> > +               host->ios.power_off_delay_us = 1000;
>
> If power-off-delay-us is specified and the value >= 0, I think we can
> respect it as is.
>
> This means we need to treat "0" a bit special and bail out in mmc_delay_us().

Ok, just to confirm, then, you want to drop these guards in mmc_of_parse
and instead catch 0 in mmc_power_off?

What if DT parse gets garbled and host->ios.power_off_delay_us < 1 is
passed?

~ Judith

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