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

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Message-ID: <20250307174643.1288695-1-erick.shepherd@ni.com>
Date: Fri, 7 Mar 2025 11:46:43 -0600
From: Erick Shepherd <erick.shepherd@...com>
To: <adrian.hunter@...el.com>
CC: <brad.mouring@...com>, <erick.shepherd@...com>,
        <gratian.crisan@...rson.com>, <kyle.roeschley@...com>,
        <linux-kernel@...r.kernel.org>, <linux-mmc@...r.kernel.org>,
        <ulf.hansson@...aro.org>
Subject: RE: [PATCH] mmc: core: Wait for Vdd to settle on card power off

>> 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?

Thank you for taking a look at this. The initial change was made in
mmc_power_off() due to an issue we had with some of our devices
requiring more time for the Vdd to drain below 0.5V. Ulf gave us this
feedback on that change:

> No, this isn't the proper place of adding more "magic" delays.

> Instead, make sure the related ->set_ios() callback in the mmc host
> driver deals with this instead. In case it uses an external regulator,
> via the regulator API, then this is something that should be
> controlled with the definition of the regulator.

Should we take a different approach here? 

Regards
Erick