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

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Replacing `mmc_delay(1)` with `mmc_delay_us(host->ios.power_off_delay_us)` (which defaults to 1000) inadvertently changes the underlying timer mechanism from `usleep_range` to `msleep(1)`, introducing a latency regression of up to ~20ms per power-off cycle.
--

--- Patch [3]: [PATCH v2 3/3] mmc: core: Add power-off-delay-us support ---
commit 028a9284e6d11b892584840a7f05aeed49d66b60
Author: Judith Mendez <jm@ti.com>

mmc: core: Add power-off-delay-us support

This commit adds support for power-off-delay-us to specify a custom delay
after deasserting power during MMC power cycles. The default delay is set
to 1000us, but can be overridden to work around hardware issues.

> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> --- 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);

[Severity: Medium]
Does this change introduce a latency regression during power management
operations?

The default value for power_off_delay_us is 1000. When mmc_delay_us() is
called with 1000 or greater, it falls into the msleep() path:

drivers/mmc/core/core.h:mmc_delay_us() {
	if (us < 1000) {
		usleep_range(us, us + (us >> 2));
	} else {
		unsigned int rem_us = us % 1000;

		msleep(us / 1000);
		if (rem_us)
			usleep_range(rem_us, rem_us + (rem_us >> 2));
	}
}

This effectively calls msleep(1), which uses jiffy-based timeouts. On
systems where HZ=100, this can delay execution by up to 20ms per power-off
cycle. The original mmc_delay(1) call correctly used the high-resolution
usleep_range(1000, 1250) timer mechanism.

Could the threshold for mmc_delay_us() be adjusted, or could usleep_range()
be used to avoid an unintended jiffy-based sleep?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260722205701.372789-1-jm@ti.com?part=3