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Message-Id: <20250616102917.1677116-4-o.rempel@pengutronix.de>
Date: Mon, 16 Jun 2025 12:29:16 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
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: [PATCH v6 3/4] mmc: core: add undervoltage handler for MMC/eMMC devices
Introduce `_mmc_handle_undervoltage()` to handle undervoltage events for
MMC/eMMC devices. The handler performs a controlled emergency suspend and
then marks the card as removed to prevent further I/O.
This is achieved by calling a new internal helper, `__mmc_suspend()`,
with `MMC_POWEROFF_UNDERVOLTAGE`. This ensures a fast power-down sequence
by using the short power-off notification and skipping the cache flush.
If power-off notify is not supported, it falls back to sleep or deselect.
Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
changes v6:
- Refactor suspend logic: move cache flush skipping during undervoltage
to a separate, preceding commit.
- update commit message
changes v5:
- Rebased on top of patch introducing enum mmc_poweroff_type
- Updated call to __mmc_suspend() to use MMC_POWEROFF_UNDERVOLTAGE
- Dropped __mmc_resume() helper, as it is no longer needed
- Updated commit message to reflect API change and code removal
changes v4:
- Drop HPI step.
changes v3:
- reword commit message.
- add comments in the code
- do not try to resume sleeping device
---
drivers/mmc/core/mmc.c | 76 ++++++++++++++++++++++++++++++++++++++++--
1 file changed, 73 insertions(+), 3 deletions(-)
diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 6812df679ba9..fe4fc2ad261e 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -2120,7 +2120,7 @@ static int _mmc_flush_cache(struct mmc_host *host)
return err;
}
-static int _mmc_suspend(struct mmc_host *host, enum mmc_poweroff_type pm_type)
+static int __mmc_suspend(struct mmc_host *host, enum mmc_poweroff_type pm_type)
{
unsigned int notify_type = EXT_CSD_POWER_OFF_SHORT;
int err = 0;
@@ -2128,8 +2128,6 @@ static int _mmc_suspend(struct mmc_host *host, enum mmc_poweroff_type pm_type)
if (pm_type == MMC_POWEROFF_SHUTDOWN)
notify_type = EXT_CSD_POWER_OFF_LONG;
- mmc_claim_host(host);
-
if (mmc_card_suspended(host->card))
goto out;
@@ -2156,7 +2154,17 @@ static int _mmc_suspend(struct mmc_host *host, enum mmc_poweroff_type pm_type)
mmc_card_set_suspended(host->card);
}
out:
+ return err;
+}
+
+static int _mmc_suspend(struct mmc_host *host, enum mmc_poweroff_type pm_type)
+{
+ int err;
+
+ mmc_claim_host(host);
+ err = __mmc_suspend(host, pm_type);
mmc_release_host(host);
+
return err;
}
@@ -2219,6 +2227,13 @@ static int mmc_shutdown(struct mmc_host *host)
{
int err = 0;
+ /*
+ * In case of undervoltage, the card will be powered off by
+ * _mmc_handle_undervoltage()
+ */
+ if (host->undervoltage)
+ return 0;
+
/*
* If the card remains suspended at this point and it was done by using
* the sleep-cmd (CMD5), we may need to re-initialize it first, to allow
@@ -2309,6 +2324,60 @@ static int _mmc_hw_reset(struct mmc_host *host)
return mmc_init_card(host, card->ocr, card);
}
+/**
+ * _mmc_handle_undervoltage - Handle an undervoltage event for MMC/eMMC devices
+ * @host: MMC host structure
+ *
+ * This function is triggered when an undervoltage condition is detected.
+ * It attempts to transition the device into a low-power or safe state to
+ * prevent data corruption.
+ *
+ * Steps performed:
+ * 1. If no card is present, return immediately.
+ * 2. Perform an emergency suspend using EXT_CSD_POWER_OFF_SHORT if possible.
+ * - If power-off notify is not supported, fallback mechanisms like sleep or
+ * deselecting the card are attempted.
+ * - Cache flushing is skipped to reduce execution time.
+ * 3. Mark the card as removed to prevent further interactions after
+ * undervoltage.
+ *
+ * Note: This function does not handle host claiming or releasing. The caller
+ * must ensure that the host is properly claimed before calling this
+ * function and released afterward.
+ *
+ * Returns: 0 on success, or a negative error code if any step fails.
+ */
+static int _mmc_handle_undervoltage(struct mmc_host *host)
+{
+ struct mmc_card *card = host->card;
+ int err;
+
+ /* If there is no card attached, nothing to do */
+ if (!card)
+ return 0;
+
+ /*
+ * Perform an emergency suspend to power off the eMMC quickly.
+ * This ensures the device enters a safe state before power is lost.
+ * We first attempt EXT_CSD_POWER_OFF_SHORT, but if power-off notify
+ * is not supported, we fall back to sleep mode or deselecting the card.
+ * Cache flushing is skipped to minimize delay.
+ */
+ err = __mmc_suspend(host, MMC_POWEROFF_UNDERVOLTAGE);
+ if (err)
+ pr_err("%s: undervoltage suspend failed: %pe\n",
+ mmc_hostname(host), ERR_PTR(err));
+
+ /*
+ * Mark the card as removed to prevent further operations.
+ * This ensures the system does not attempt to access the device
+ * after an undervoltage event, avoiding potential corruption.
+ */
+ mmc_card_set_removed(card);
+
+ return err;
+}
+
static const struct mmc_bus_ops mmc_ops = {
.remove = mmc_remove,
.detect = mmc_detect,
@@ -2321,6 +2390,7 @@ static const struct mmc_bus_ops mmc_ops = {
.hw_reset = _mmc_hw_reset,
.cache_enabled = _mmc_cache_enabled,
.flush_cache = _mmc_flush_cache,
+ .handle_undervoltage = _mmc_handle_undervoltage,
};
/*
--
2.39.5
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