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

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Message-ID: <440723b0-a1fa-4f9f-90f4-50dc831c68e5@intel.com>
Date: Fri, 7 Mar 2025 20:53:43 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Erick Shepherd <erick.shepherd@...com>
CC: <brad.mouring@...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

On 7/03/25 19:46, 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?
> 
> 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? 

It probably should be dealt with in the ->set_power() callback.
Is it one of the PCI devices in sdhci-pci-core.c?