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

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?

~ Judith

~ Judith