sdmmc_host: implement sd_enable()

commit 72dd8bc4d05f41b3bc93515657c9835b4c305367
Author: Aidan MacDonald <[email protected]>
Date:   Tue Jan 13 16:06:34 2026 +0000

    sdmmc_host: implement sd_enable()
    
    This is mainly useful for bootloaders that want to safely
    disable the SD/MMC controller before booting. Disabling a
    controller will reset and power down the bus; all attempts
    to read or write to a disabled controller will fail.
    
    Change-Id: I4a7ec4287f2b8510a35d964cc806c74be8c86406

diff --git a/firmware/drivers/sdmmc_host.c b/firmware/drivers/sdmmc_host.c
index e7110c64d1..c012731a7e 100644
--- a/firmware/drivers/sdmmc_host.c
+++ b/firmware/drivers/sdmmc_host.c
@@ -114,6 +114,7 @@ void sdmmc_host_init(struct sdmmc_host *host,
             host->ops = ops;
             host->controller = controller;
             host->present = !config->is_removable;
+            host->enabled = true;
             mutex_init(&host->lock);
 
             array[i] = host;
@@ -188,6 +189,26 @@ static void sdmmc_host_bus_reset(struct sdmmc_host *host)
     memset(&host->cardinfo, 0, sizeof(host->cardinfo));
 }
 
+/*
+ * Call to enable/disable the host controller. If disabled then the
+ * controller and device are powered off and no access to the storage
+ * device is allowed.
+ */
+static void sdmmc_host_set_enabled(struct sdmmc_host *host, bool enabled)
+{
+    mutex_lock(&host->lock);
+
+    if (enabled != host->enabled)
+    {
+        if (host->enabled)
+            sdmmc_host_bus_reset(host);
+
+        host->enabled = enabled;
+    }
+
+    mutex_unlock(&host->lock);
+}
+
 #ifdef HAVE_HOTSWAP
 static void sdmmc_host_hotswap_event(struct sdmmc_host *host, bool is_present)
 {
@@ -629,6 +650,9 @@ static int sdmmc_host_transfer(struct sdmmc_host *host,
 
     mutex_lock(&host->lock);
 
+    if (!host->enabled)
+        goto out;
+
     if (!sdmmc_host_medium_present(host))
         goto out;
 
@@ -721,6 +745,16 @@ tCardInfo *card_get_info_target(int drive)
     return &sdmmc_sd_hosts[drive]->cardinfo;
 }
 
+void sd_enable(bool enabled)
+{
+    for (size_t i = 0; i < ARRAYLEN(sdmmc_sd_hosts); ++i)
+    {
+        struct sdmmc_host *host = sdmmc_sd_hosts[i];
+
+        sdmmc_host_set_enabled(host, enabled);
+    }
+}
+
 long sd_last_disk_activity(void)
 {
     return sdmmc_sd_last_activity;
diff --git a/firmware/export/sdmmc_host.h b/firmware/export/sdmmc_host.h
index 7aa48e5f9e..1d00c94a27 100644
--- a/firmware/export/sdmmc_host.h
+++ b/firmware/export/sdmmc_host.h
@@ -231,6 +231,7 @@ struct sdmmc_host
     struct mutex lock;
 
     /* Bus & device state flags; must only be accessed with lock held */
+    bool enabled     : 1;
     bool need_reset  : 1;
     bool powered     : 1;
     bool initialized : 1;
-- 
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