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

On 8/4/2026 6:02 AM, Ulf Hansson wrote:
> 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?

Ok, will do that. Thanks. Will send out v3.

~ Judith

> 
> Kind regards
> Uffe