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

[Mendez, Judith]

Hi Ulf,

On 8/3/2026 7:27 AM, Ulf Hansson wrote:
> On Tue, Jul 28, 2026 at 11:56 PM Judith Mendez <jm@xxxxxx> wrote:
> > 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?
>
> Not exactly, if mmc_of_parse() doesn't get a valid value (>=0) when
> parsing for "power-off-delay-us" it should not set
> host->ios.power_off_delay_us, but rather rely on the default value
> that we have set in mmc_alloc_host().

Ok, so

if power-off-delay-us < 0 -> use host default
else power_off_delay_us = power-off-delay-us

And in mmc_power_off(), if power_off_delay_us = 0
what would you like to do with special case?

~ Judith

~ Judith