Message-ID: <CAPDyKFo5tJHEb8o892vg9DoMsLTq+715gotqnP26hMWenvjg8A@mail.gmail.com>
Date: Fri, 22 Aug 2025 12:17:23 +0200
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 v9 0/2] mmc: handle undervoltage events and prevent eMMC corruption

On Thu, 21 Aug 2025 at 15:07, Oleksij Rempel <o.rempel@...gutronix.de> wrote:
>
> changes v9:
> - Drop stray whitespace after mmc_claim_host() in mmc_attach_mmc()
> - Remove unnecessary #include <linux/workqueue.h> from host.h,
>   add forward declarations instead
> - Move internal prototypes for undervoltage helpers
>   (mmc_regulator_register/unregister_undervoltage_notifier(),
>    mmc_undervoltage_workfn()) from host.h to core.h
> - remove host->card check
> changes v8:
> - fix compile warning
> changes v7:
> - Remove all usage of the redundant undervoltage_notify_registered flag
> - Register undervoltage notifier in mmc_add_card() after setting card as
>   present, for all supported cards.
> - Unregister undervoltage notifier in mmc_remove_card() based on card presence
> - Remove all unnecessary EXPORT_SYMBOL_GPL for functions only used within MMC
>   core.
> - Move all host claiming and releasing responsibility for undervoltage events
>   into the bus_ops callback;
> - add comment for host->undervoltage
> - Squash undervoltage suspend preparation and handler into one patch.
> - Use mmc_card_removed() in shutdown path instead of host->undervoltage.
> - Remove redundant card presence check in undervoltage handler.
> changes v6:
> - Rewrite commit message to be more technical per reviewer feedback.
> - Address race conditions by using __mmc_stop_host() instead of only
>   claiming the host in the undervoltage handler.
> - Move notifier registration from mmc_regulator_get_supply() to the end of
>   a successful card initialization in mmc_attach_mmc(), ensuring it only
>   runs for capable cards.
> - Centralize notifier unregistration in mmc_remove_card() to correctly
>   handle all card removal and error paths.
> - Add 'undervoltage_notify_registered' flag to struct mmc_host to
>   reliably track the notifier state.
> - Consolidate multiple notifier callbacks into a single, generic handler.
> - Remove premature notifier support for vqmmc and vqmmc2 regulators.
> - Move INIT_WORK() for the undervoltage workqueue to mmc_alloc_host().
> changes v5:
> - Rebased on top of mmc/next after introduction of enum mmc_poweroff_type
> - Replaced boolean undervoltage parameter with MMC_POWEROFF_UNDERVOLTAGE
> - Dropped unused __mmc_resume() helper
> - Updated commit messages accordingly
> 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.
>
> ## 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 (2):
>   mmc: core: Add infrastructure for undervoltage handling
>   mmc: core: add undervoltage handler for MMC/eMMC devices
>
>  drivers/mmc/core/bus.c       | 12 ++++++
>  drivers/mmc/core/core.c      | 23 +++++++++++
>  drivers/mmc/core/core.h      |  5 +++
>  drivers/mmc/core/host.c      |  2 +
>  drivers/mmc/core/mmc.c       | 70 ++++++++++++++++++++++++++++++--
>  drivers/mmc/core/regulator.c | 77 ++++++++++++++++++++++++++++++++++++
>  include/linux/mmc/host.h     | 11 ++++++
>  7 files changed, 197 insertions(+), 3 deletions(-)
>
> --
> 2.39.5
>

This is nice work - and I appreciated all your efforts you have put in
to get this done!

The series applied for next, thanks!

Kind regards
Uffe

Powered by blists - more mailing lists