[PATCH v3 6/6] mmc: sdhci: prevent command execution after undervoltage shutdown

[Oleksij Rempel]

Introduce an emergency_stop flag in struct mmc_host to block further
MMC/SD commands after an undervoltage shutdown. If emergency_stop is
set, sdhci_send_command() will reject new requests with -EBUSY and log a
warning. This helps diagnose and identify code paths that may still
attempt writes after the undervoltage shutdown sequence has completed.

Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
---
changes v3:
- add comments
---
 drivers/mmc/core/mmc.c   | 7 +++++++
 drivers/mmc/host/sdhci.c | 9 +++++++++
 include/linux/mmc/host.h | 1 +
 3 files changed, 17 insertions(+)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index a50cdd550a22..0cd6b81d0678 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -2370,6 +2370,13 @@ static int _mmc_handle_undervoltage(struct mmc_host *host)
 	 */
 	mmc_card_set_removed(card);
 
+	/*
+	 * Signal the host controller driver that we are in emergency stop mode.
+	 * This prevents any new storage requests from being issued, ensuring
+	 * that no further operations take place while in this state.
+	 */
+	host->emergency_stop = true;
+
 	return err;
 }
 
diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index f4a7733a8ad2..8d67f27e7d9e 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -1658,6 +1658,15 @@ static bool sdhci_send_command(struct sdhci_host *host, struct mmc_command *cmd)
 
 	WARN_ON(host->cmd);
 
+	if (host->mmc->emergency_stop) {
+		pr_warn("%s: Ignoring normal request, emergency stop is active\n",
+			mmc_hostname(host->mmc));
+		WARN_ON_ONCE(1);
+
+		cmd->error = -EBUSY;
+		return true;
+	}
+
 	/* Initially, a command has no error */
 	cmd->error = 0;
 
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 4e147ad82804..5dfe2cdde59f 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -501,6 +501,7 @@ struct mmc_host {
 	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 */
+	unsigned int		emergency_stop:1; /* Emergency stop. No transfers are allowed. */
 
 	int			rescan_disable;	/* disable card detection */
 	int			rescan_entered;	/* used with nonremovable devices */
-- 
2.39.5