@@ -394,6 +394,11 @@ void mmc_remove_card(struct mmc_card *card)
{
struct mmc_host *host = card->host;
+ if (host->undervoltage_notify_registered) {
+ mmc_regulator_unregister_undervoltage_notifier(host);
+ host->undervoltage_notify_registered = false;
+ }
+
mmc_remove_card_debugfs(card);
if (mmc_card_present(card)) {
@@ -1399,6 +1399,39 @@ void mmc_power_cycle(struct mmc_host *host, u32 ocr)
mmc_power_up(host, ocr);
}
+/**
+ * mmc_handle_undervoltage - Handle an undervoltage event on the MMC bus
+ * @host: The MMC host that detected the undervoltage condition
+ *
+ * This function is called when an undervoltage event is detected on one of
+ * the MMC regulators.
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+int mmc_handle_undervoltage(struct mmc_host *host)
+{
+ int ret;
+
+ /* Stop the host to prevent races with card removal */
+ __mmc_stop_host(host);
+
+ mmc_claim_host(host);
+
+ if (!host->bus_ops || !host->bus_ops->handle_undervoltage) {
+ mmc_release_host(host);
+ return 0;
+ }
+
+ dev_warn(mmc_dev(host), "%s: Undervoltage detected, initiating emergency stop\n",
+ mmc_hostname(host));
+
+ ret = host->bus_ops->handle_undervoltage(host);
+
+ mmc_release_host(host);
+
+ return ret;
+}
+
/*
* Assign a mmc bus handler to a host. Only one bus handler may control a
* host at any given time.
@@ -31,6 +31,7 @@ struct mmc_bus_ops {
int (*sw_reset)(struct mmc_host *);
bool (*cache_enabled)(struct mmc_host *);
int (*flush_cache)(struct mmc_host *);
+ int (*handle_undervoltage)(struct mmc_host *host);
};
void mmc_attach_bus(struct mmc_host *host, const struct mmc_bus_ops *ops);
@@ -59,6 +60,7 @@ void mmc_power_off(struct mmc_host *host);
void mmc_power_cycle(struct mmc_host *host, u32 ocr);
void mmc_set_initial_state(struct mmc_host *host);
u32 mmc_vddrange_to_ocrmask(int vdd_min, int vdd_max);
+int mmc_handle_undervoltage(struct mmc_host *host);
static inline void mmc_delay(unsigned int ms)
{
@@ -564,6 +564,9 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
INIT_WORK(&host->sdio_irq_work, sdio_irq_work);
timer_setup(&host->retune_timer, mmc_retune_timer, 0);
+ INIT_WORK(&host->supply.uv_work, mmc_undervoltage_workfn);
+ host->undervoltage_notify_registered = false;
+
/*
* By default, hosts do not support SGIO or large requests.
* They have to set these according to their abilities.
@@ -2370,6 +2370,12 @@ int mmc_attach_mmc(struct mmc_host *host)
goto remove_card;
mmc_claim_host(host);
+
+ if (host->card->ext_csd.power_off_notification == EXT_CSD_POWER_ON) {
+ mmc_regulator_register_undervoltage_notifier(host);
+ host->undervoltage_notify_registered = true;
+ }
+
return 0;
remove_card:
@@ -7,6 +7,7 @@
#include <linux/err.h>
#include <linux/log2.h>
#include <linux/regulator/consumer.h>
+#include <linux/workqueue.h>
#include <linux/mmc/host.h>
@@ -262,6 +263,87 @@ static inline int mmc_regulator_get_ocrmask(struct regulator *supply)
#endif /* CONFIG_REGULATOR */
+/* To be called from a high-priority workqueue */
+void mmc_undervoltage_workfn(struct work_struct *work)
+{
+ struct mmc_supply *supply;
+ struct mmc_host *host;
+
+ supply = container_of(work, struct mmc_supply, uv_work);
+ host = container_of(supply, struct mmc_host, supply);
+
+ mmc_handle_undervoltage(host);
+}
+EXPORT_SYMBOL_GPL(mmc_undervoltage_workfn);
+
+static int mmc_handle_regulator_event(struct notifier_block *nb,
+ unsigned long event, void *data)
+{
+ struct mmc_supply *supply = container_of(nb, struct mmc_supply,
+ vmmc_nb);
+ struct mmc_host *host = container_of(supply, struct mmc_host, supply);
+ unsigned long flags;
+
+ switch (event) {
+ case REGULATOR_EVENT_UNDER_VOLTAGE:
+ spin_lock_irqsave(&host->lock, flags);
+ if (host->undervoltage) {
+ spin_unlock_irqrestore(&host->lock, flags);
+ return NOTIFY_OK;
+ }
+
+ host->undervoltage = true;
+ spin_unlock_irqrestore(&host->lock, flags);
+
+ queue_work(system_highpri_wq, &host->supply.uv_work);
+ break;
+ default:
+ return NOTIFY_DONE;
+ }
+
+ return NOTIFY_OK;
+}
+
+/**
+ * mmc_regulator_register_undervoltage_notifier - Register for undervoltage
+ * events
+ * @host: MMC host
+ *
+ * To be called by a bus driver when a card supporting graceful shutdown
+ * is attached.
+ */
+void mmc_regulator_register_undervoltage_notifier(struct mmc_host *host)
+{
+ int ret;
+
+ if (IS_ERR_OR_NULL(host->supply.vmmc))
+ return;
+
+ host->supply.vmmc_nb.notifier_call = mmc_handle_regulator_event;
+ ret = regulator_register_notifier(host->supply.vmmc,
+ &host->supply.vmmc_nb);
+ if (ret)
+ dev_warn(mmc_dev(host), "Failed to register vmmc notifier: %d\n", ret);
+}
+EXPORT_SYMBOL_GPL(mmc_regulator_register_undervoltage_notifier);
+
+/**
+ * mmc_regulator_unregister_undervoltage_notifier - Unregister undervoltage
+ * notifier
+ * @host: MMC host
+ */
+void mmc_regulator_unregister_undervoltage_notifier(struct mmc_host *host)
+{
+ if (IS_ERR_OR_NULL(host->supply.vmmc))
+ return;
+
+ regulator_unregister_notifier(host->supply.vmmc, &host->supply.vmmc_nb);
+
+ /* Ensure any pending work is flushed before the card is removed */
+ cancel_work_sync(&host->supply.uv_work);
+}
+EXPORT_SYMBOL_GPL(mmc_regulator_unregister_undervoltage_notifier);
+
/**
* mmc_regulator_get_supply - try to get VMMC and VQMMC regulators for a host
* @mmc: the host to regulate
@@ -11,6 +11,7 @@
#include <linux/device.h>
#include <linux/fault-inject.h>
#include <linux/debugfs.h>
+#include <linux/workqueue.h>
#include <linux/mmc/core.h>
#include <linux/mmc/card.h>
@@ -342,6 +343,9 @@ struct mmc_supply {
struct regulator *vmmc; /* Card power supply */
struct regulator *vqmmc; /* Optional Vccq supply */
struct regulator *vqmmc2; /* Optional supply for phy */
+
+ struct notifier_block vmmc_nb; /* Notifier for vmmc */
+ struct work_struct uv_work; /* Undervoltage work */
};
struct mmc_ctx {
@@ -493,6 +497,9 @@ struct mmc_host {
unsigned int retune_crc_disable:1; /* don't trigger retune upon crc */
unsigned int can_dma_map_merge:1; /* merging can be used */
unsigned int vqmmc_enabled:1; /* vqmmc regulator is enabled */
+ unsigned int undervoltage:1; /* Undervoltage state */
+ /* Undervoltage notifier is registered */
+ unsigned int undervoltage_notify_registered:1;
int rescan_disable; /* disable card detection */
int rescan_entered; /* used with nonremovable devices */
@@ -659,6 +666,9 @@ static inline int mmc_regulator_set_vqmmc2(struct mmc_host *mmc,
int mmc_regulator_get_supply(struct mmc_host *mmc);
int mmc_regulator_enable_vqmmc(struct mmc_host *mmc);
void mmc_regulator_disable_vqmmc(struct mmc_host *mmc);
+void mmc_regulator_register_undervoltage_notifier(struct mmc_host *host);
+void mmc_regulator_unregister_undervoltage_notifier(struct mmc_host *host);
+void mmc_undervoltage_workfn(struct work_struct *work);
static inline int mmc_card_is_removable(struct mmc_host *host)
{
Implement the core infrastructure to allow MMC bus types to handle REGULATOR_EVENT_UNDER_VOLTAGE events from power regulators. This is primarily aimed at allowing devices like eMMC to perform an emergency shutdown to prevent data corruption when a power failure is imminent. This patch introduces: - A new 'handle_undervoltage' function pointer to 'struct mmc_bus_ops'. Bus drivers (e.g., for eMMC) can implement this to define their emergency procedures. - A workqueue ('uv_work') in 'struct mmc_supply' to handle the event asynchronously in a high-priority context. - A new function 'mmc_handle_undervoltage()' which is called from the workqueue. It stops the host queue to prevent races with card removal, checks for the bus op, and invokes the handler. - Functions to register and unregister the regulator notifier, intended to be called by bus drivers like 'mmc_attach_mmc' when a compatible card is detected. The notifier is only registered for the main 'vmmc' supply, as undervoltage handling for 'vqmmc' or 'vqmmc2' is not required at this time. Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de> --- 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 v3: - filter supported cards at early stage - add locking in mmc_handle_regulator_event() - claim/release host in mmc_handle_undervoltage() Background & Decision at LPC24: This solution was proposed and refined during LPC24 in the talk "Graceful Under Pressure: Prioritizing Shutdown to Protect Your Data in Embedded Systems," which aimed to address how Linux should handle power fluctuations in embedded devices to prevent data corruption or storage damage. At the time, multiple possible solutions were considered: 1. Triggering a system-wide suspend or shutdown: when undervoltage is detected, with device-specific prioritization to ensure critical components shut down first. - This approach was disliked by Greg Kroah-Hartman, as it introduced complexity and was not suitable for all use cases. 2. Notifying relevant devices through the regulator framework: to allow graceful per-device handling. - This approach was agreed upon as the most acceptable by participants in the discussion, including Greg Kroah-Hartman, Mark Brown, and Rafael J. Wysocki. - This patch implements that decision by integrating undervoltage handling into the MMC subsystem. --- drivers/mmc/core/bus.c | 5 +++ drivers/mmc/core/core.c | 33 +++++++++++++++ drivers/mmc/core/core.h | 2 + drivers/mmc/core/host.c | 3 ++ drivers/mmc/core/mmc.c | 6 +++ drivers/mmc/core/regulator.c | 82 ++++++++++++++++++++++++++++++++++++ include/linux/mmc/host.h | 10 +++++ 7 files changed, 141 insertions(+)