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

On Mon, Aug 3, 2026 at 4:31 PM Mendez, Judith <[email protected]> wrote:
>
> Hi Ulf,
>
> On 8/3/2026 7:27 AM, Ulf Hansson wrote:
> > On Tue, Jul 28, 2026 at 11:56 PM 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 PM Judith Mendez <[email protected]> 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 <[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 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?

Well, we need to bail out somewhere. :-)

I guess mmc_power_off() will call mmc_delay_us()? In that case,
mmc_delay_us() could just return immediately if the delay is 0?

Kind regards
Uffe