linux-kernel - Re: [PATCH v4 0/4] mmc: handle undervoltage events and prevent eMMC corruption

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Message-ID: <CAPDyKFrC56BBJk=YAPWCCNYNqFAoY74_yH0ZXfNQEiDhaA2xJg@mail.gmail.com>
Date: Thu, 20 Mar 2025 15:36:32 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: kernel@...gutronix.de, linux-kernel@...r.kernel.org, 
	linux-mmc@...r.kernel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Mark Brown <broonie@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>, Søren Andersen <san@...v.dk>, 
	Christian Loehle <christian.loehle@....com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Avri Altman <Avri.Altman@...disk.com>
Subject: Re: [PATCH v4 0/4] mmc: handle undervoltage events and prevent eMMC corruption

Hi Oleksij,

On Mon, 10 Mar 2025 at 11:22, Oleksij Rempel <o.rempel@...gutronix.de> wrote:
>
> changes v4:
> - drop HPI and SDHCI related patches
>
> This patch set introduces a framework for handling undervoltage events
> in the MMC subsystem. The goal is to improve system reliability by
> ensuring graceful handling of power fluctuations that could otherwise
> lead to metadata corruption, potentially rendering the eMMC chip
> unusable or causing significant data loss.

Thanks for posting this! I will spend some time reviewing this next
week and let you know my comments then.

However, I just wanted to let you know that I just posted a series [1]
(forgot to cc you, sorry), which also reworks the way _mmc_suspend()
understands what scenario it should be running. I am guessing that
re-work is simplifying for your $subject series too. Maybe you would
like to have a look?

Kind regards
Uffe

[1]
https://lore.kernel.org/all/20250320140040.162416-1-ulf.hansson@linaro.org/



>
> ## Problem Statement
>
> Power fluctuations and sudden losses can leave eMMC devices in an
> undefined state, leading to severe consequences. The worst case can
> result in metadata corruption, making the entire storage inaccessible.
> While some eMMC devices promise to handle such situations internally,
> experience shows that some chip variants are still affected. This has
> led vendors to take a more protective approach, implementing external
> undervoltage handling as a precautionary measure to avoid costly field
> failures and returns.
>
> The existence of the "Power Off Notification" feature in the eMMC
> standard itself serves as indirect evidence that this is a real-world
> issue.  While some projects have already faced the consequences of
> ignoring this problem (often at significant cost), specific cases cannot
> be disclosed due to NDAs.
>
> ## Challenges and Implementation Approach
>
> 1. **Raising awareness of the problem**: While vendors have used
>    proprietary solutions for years, a unified approach is needed upstream.
>    This patch set is a first step in making that happen.
>
> 2. **Finding an acceptable implementation path**: There are multiple
>    ways to handle undervoltage - either in the kernel or in user space,
>    through a global shutdown mechanism, or using the regulator framework.
>    This patch set takes the kernel-based approach but does not prevent
>    future extensions, such as allowing user-space handoff once available.
>
> 3. **Preparing for vendor adoption and testing**: By providing a
>    structured solution upstream, this patch set lowers the barrier for
>    vendors to standardize their undervoltage handling instead of relying on
>    fragmented, out-of-tree implementations.
>
> ## Current Limitations
>
> This patch set is an initial step and does not yet cover all possible
> design restrictions or edge cases. Future improvements may include
> better coordination with user space and enhancements based on broader
> testing.
>
> ## Testing Details
>
> The implementation was tested on an iMX8MP-based system. The board had
> approximately 100ms of available power hold-up time. The Power Off
> Notification was sent ~4ms after the board was detached from the power
> supply, allowing sufficient time for the eMMC to handle the event
> properly.  Tests were conducted under both idle conditions and active
> read/write operations.
>
> Oleksij Rempel (4):
>   mmc: core: Handle undervoltage events and register regulator notifiers
>   mmc: core: refactor _mmc_suspend() for undervoltage handling
>   mmc: core: add undervoltage handler for MMC/eMMC devices
>   mmc: block: abort requests and suppress errors after undervoltage
>     shutdown
>
>  drivers/mmc/core/block.c     |   2 +-
>  drivers/mmc/core/core.c      |  30 +++++++++
>  drivers/mmc/core/core.h      |   2 +
>  drivers/mmc/core/mmc.c       | 127 +++++++++++++++++++++++++++++------
>  drivers/mmc/core/queue.c     |   2 +-
>  drivers/mmc/core/regulator.c | 124 ++++++++++++++++++++++++++++++++++
>  include/linux/mmc/host.h     |   8 +++
>  7 files changed, 274 insertions(+), 21 deletions(-)
>
> --
> 2.39.5
>