linux-kernel - Re: [PATCH] mmc: core: Wait for Vdd to settle on card power off

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Message-ID: <35aebb39-ae2e-4186-8de4-6830ec661f4d@intel.com>
Date: Wed, 5 Mar 2025 20:38:42 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Erick Shepherd <erick.shepherd@...com>, <linux-kernel@...r.kernel.org>
CC: <linux-mmc@...r.kernel.org>, <ulf.hansson@...aro.org>,
	<gratian.crisan@...rson.com>, Kyle Roeschley <kyle.roeschley@...com>, "Brad
 Mouring" <brad.mouring@...com>
Subject: Re: [PATCH] mmc: core: Wait for Vdd to settle on card power off

On 11/02/25 23:46, Erick Shepherd wrote:
> The SD spec version 6.0 section 6.4.1.5 requires that Vdd must be
> lowered to less than 0.5V for a minimum of 1 ms when powering off a
> card. Increase our wait to 15 ms so that voltage has time to drain down
> to 0.5V.

mmc_power_off() has a delay.  So does mmc_power_cycle()

Why does this need to be in sdhci?  Are you experiencing an
issue?

> 
> Signed-off-by: Kyle Roeschley <kyle.roeschley@...com>
> Signed-off-by: Brad Mouring <brad.mouring@...com>
> Signed-off-by: Erick Shepherd <erick.shepherd@...com>
> ---
>  drivers/mmc/host/sdhci.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index f4a7733a8ad2..b15a1f107549 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -2415,6 +2415,9 @@ void sdhci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
>  	else
>  		sdhci_set_power(host, ios->power_mode, ios->vdd);
>  
> +	if (ios->power_mode == MMC_POWER_OFF)
> +		mdelay(15);
> +
>  	if (host->ops->platform_send_init_74_clocks)
>  		host->ops->platform_send_init_74_clocks(host, ios->power_mode);
>