--- zzzz-none-000/linux-5.15.111/drivers/mtd/devices/block2mtd.c	2023-05-11 14:00:40.000000000 +0000
+++ puma7-atom-6670-761/linux-5.15.111/drivers/mtd/devices/block2mtd.c	2024-02-07 10:23:07.000000000 +0000
@@ -30,6 +30,8 @@
 #include <linux/mount.h>
 #include <linux/slab.h>
 #include <linux/major.h>
+#include <linux/mmc/host.h>
+#include <linux/mmc/card.h>
 
 /* Info for the block device */
 struct block2mtd_dev {
@@ -37,6 +39,9 @@
 	struct block_device *blkdev;
 	struct mtd_info mtd;
 	struct mutex write_mutex;
+#if defined(CONFIG_TFFS_PANIC_LOG)
+	bool in_panic;  // AVM: Set for synchronous access
+#endif
 };
 
 
@@ -81,6 +86,12 @@
 	}
 	return 0;
 }
+
+static sector_t to_sector(const struct block_device *bdev, loff_t off)
+{
+	return bdev->bd_start_sect + (off >> 9);
+}
+
 static int block2mtd_erase(struct mtd_info *mtd, struct erase_info *instr)
 {
 	struct block2mtd_dev *dev = mtd->priv;
@@ -88,6 +99,34 @@
 	size_t len = instr->len;
 	int err;
 
+#if defined(CONFIG_TFFS_PANIC_LOG)
+	if (dev->in_panic) {
+		struct block_device *bdev = dev->blkdev;
+		struct mmc_host *mmc;
+		u8 erasedblock[512];
+		sector_t sect;
+		size_t blocks;
+
+		mmc = mmc_blk_get_host(bdev->bd_disk);
+		if (IS_ERR_OR_NULL(mmc))
+			return -ENODEV;
+
+		memset(erasedblock, 0xFF, sizeof(erasedblock));
+		blocks = DIV_ROUND_UP(len, sizeof(erasedblock));
+		sect = to_sector(bdev, from);
+
+		while (blocks) {
+			err = mmc->ops->avm_sync_io_rw_blocks(mmc, sect,
+					sizeof(erasedblock), erasedblock, NULL);
+			if (err)
+				break;
+			--blocks;
+			++sect;
+		}
+		return err;
+	}
+#endif
+
 	mutex_lock(&dev->write_mutex);
 	err = _block2mtd_erase(dev, from, len);
 	mutex_unlock(&dev->write_mutex);
@@ -97,6 +136,28 @@
 	return err;
 }
 
+#ifdef CONFIG_TFFS_PANIC_LOG
+static int block2mtd_sync_io_blocks(struct block2mtd_dev *dev, loff_t off, size_t len,
+		size_t *retlen, u_char *in, const u_char *out)
+{
+	struct block_device *bdev = dev->blkdev;
+	struct mmc_host *mmc;
+	int ret;
+
+	if (!dev->in_panic)
+		return -EBUSY;
+
+	mmc = mmc_blk_get_host(bdev->bd_disk);
+	if (IS_ERR_OR_NULL(mmc))
+		return -ENODEV;
+
+	ret = mmc->ops->avm_sync_io_rw_blocks(mmc, to_sector(bdev, off),
+			len, in, out);
+	if (retlen)
+		*retlen = ret ? 0 : len;
+	return ret;
+}
+#endif
 
 static int block2mtd_read(struct mtd_info *mtd, loff_t from, size_t len,
 		size_t *retlen, u_char *buf)
@@ -107,6 +168,11 @@
 	int offset = from & (PAGE_SIZE-1);
 	int cpylen;
 
+#if defined(CONFIG_TFFS_PANIC_LOG)
+	if (dev->in_panic)
+		return block2mtd_sync_io_blocks(dev, from, len, retlen,
+				buf, NULL);
+#endif
 	while (len) {
 		if ((offset + len) > PAGE_SIZE)
 			cpylen = PAGE_SIZE - offset;	// multiple pages
@@ -178,6 +244,11 @@
 	struct block2mtd_dev *dev = mtd->priv;
 	int err;
 
+#if defined(CONFIG_TFFS_PANIC_LOG)
+	if (dev->in_panic)
+		return block2mtd_sync_io_blocks(dev, to, len, retlen,
+				NULL, buf);
+#endif
 	mutex_lock(&dev->write_mutex);
 	err = _block2mtd_write(dev, buf, to, len, retlen);
 	mutex_unlock(&dev->write_mutex);
@@ -191,10 +262,53 @@
 static void block2mtd_sync(struct mtd_info *mtd)
 {
 	struct block2mtd_dev *dev = mtd->priv;
+
+#if defined(CONFIG_TFFS_PANIC_LOG)
+	/* We are always synced in panic. */
+	if (dev->in_panic)
+		return;
+#endif
 	sync_blockdev(dev->blkdev);
 	return;
 }
 
+#if defined(CONFIG_TFFS_PANIC_LOG)
+/*
+ * Call this to start using synchronous low level read/write functions in case
+ * of panic.
+ *
+ * Note: This only works if the bdev attached to this block2mtd is a emmc
+ *       flash with sdhci host.
+ */
+static struct mtd_info *block2mtd_sync_io_init(struct mtd_info *mtd)
+{
+	struct block2mtd_dev *dev = mtd->priv;
+	struct gendisk *disk = dev->blkdev->bd_disk;
+	struct mmc_host *mmc;
+
+	mmc = mmc_blk_get_host(disk);
+	if (IS_ERR_OR_NULL(mmc))
+		return NULL;
+
+	if (!mmc->ops->avm_sync_io_init || !mmc->ops->avm_sync_io_rw_blocks ||
+			!mmc->ops->avm_sync_io_init) {
+		dev_err(disk_to_dev(disk),
+				"%s: disk driver does not support "
+					"synchronous panic I/O\n",
+				__func__);
+		return NULL;
+	}
+
+	/* If this fails we might as well crash... */
+	if (mmc->ops->avm_sync_io_init(mmc))
+		return NULL;
+
+	dev->in_panic = true;
+
+	return mtd;
+}
+#endif
+
 
 static void block2mtd_free_device(struct block2mtd_dev *dev)
 {
@@ -296,6 +410,10 @@
 	dev->mtd._read = block2mtd_read;
 	dev->mtd.priv = dev;
 	dev->mtd.owner = THIS_MODULE;
+#ifdef CONFIG_TFFS_PANIC_LOG
+	dev->mtd.dev.parent = &bdev->bd_device;
+	dev->mtd.avm_sync_io_init = block2mtd_sync_io_init;
+#endif
 
 	if (mtd_device_register(&dev->mtd, NULL, 0)) {
 		/* Device didn't get added, so free the entry */