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

On Tue, Jul 28, 2026 at 11:56=E2=80=AFPM Judith Mendez <[email protected]> wrote:
>
> Hi Ulf,
>
> On 7/27/26 10:16 AM, Ulf Hansson wrote:
> > On Wed, Jul 22, 2026 at 10:57=E2=80=AFPM Judith Mendez <[email protected]> wrot=
e:
> >>
> >> 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 <[email protected]>
> >> ---
> >> 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 ca=
rd
> >>           * 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 =3D 1000;
> >
> > If power-off-delay-us is specified and the value >=3D 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 (>=3D0) 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().

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

See above.

>
> ~ Judith
>
> ...

Kind regards
Uffe