[PATCH v4 3/4] mmc: block: Add helper to look up mmc_card by device name

[Kamal Dasu <kamal.dasu@broadcom.com>]

Add mmc_blk_get_card_by_name() which resolves an MMC block device
name (e.g., "mmcblk1") to its associated struct mmc_card by opening
the block device and traversing gendisk to the mmc_blk_data private
data.

This is needed by the mmcpstore backend driver to find the card
associated with a given pstore_blk block device path. When mmcpstore
is built as a module, the eMMC card is already probed by the time the
module loads, so the helper can look it up directly.

Signed-off-by: Kamal Dasu <kamal.dasu@broadcom.com>
---
 drivers/mmc/core/block.c | 54 ++++++++++++++++++++++++++++++++++++++++
 drivers/mmc/core/block.h |  4 +++
 2 files changed, 58 insertions(+)

diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
index 05ee76cb0a08..91e3a778d5b2 100644
--- a/drivers/mmc/core/block.c
+++ b/drivers/mmc/core/block.c
@@ -3441,6 +3441,60 @@ static void __exit mmc_blk_exit(void)
 	bus_unregister(&mmc_rpmb_bus_type);
 }
 
+/**
+ * mmc_blk_get_card_by_name - Get mmc_card from device name
+ * @device_name: Name of the MMC device (e.g., "mmcblk1")
+ *
+ * Resolves an MMC block device name to its associated struct mmc_card.
+ * Used by the mmcpstore backend driver (when built as a module) to find
+ * the card associated with a given pstore_blk block device path.
+ *
+ * Returns: mmc_card pointer on success, NULL on failure
+ */
+struct mmc_card *mmc_blk_get_card_by_name(const char *device_name)
+{
+	struct file *bdev_file;
+	struct block_device *bdev;
+	struct gendisk *disk;
+	struct mmc_blk_data *md;
+	struct mmc_card *card = NULL;
+	char dev_path[32];
+
+	if (!device_name)
+		return NULL;
+
+	snprintf(dev_path, sizeof(dev_path), "/dev/%s", device_name);
+
+	bdev_file = bdev_file_open_by_path(dev_path, BLK_OPEN_READ, NULL, NULL);
+	if (IS_ERR(bdev_file)) {
+		pr_debug("mmc_blk: Failed to open block device %s: %ld\n",
+			 dev_path, PTR_ERR(bdev_file));
+		return NULL;
+	}
+	bdev = file_bdev(bdev_file);
+
+	disk = bdev->bd_disk;
+	if (!disk) {
+		pr_err("mmc_blk: No gendisk found for %s\n", dev_path);
+		goto out_put_bdev;
+	}
+
+	md = disk->private_data;
+	if (!md) {
+		pr_debug("mmc_blk: No mmc_blk_data found for %s\n", dev_path);
+		goto out_put_bdev;
+	}
+
+	card = md->queue.card;
+	if (!card)
+		pr_err("mmc_blk: No mmc_card found for %s\n", dev_path);
+
+out_put_bdev:
+	fput(bdev_file);
+	return card;
+}
+EXPORT_SYMBOL_GPL(mmc_blk_get_card_by_name);
+
 module_init(mmc_blk_init);
 module_exit(mmc_blk_exit);
 
diff --git a/drivers/mmc/core/block.h b/drivers/mmc/core/block.h
index 31153f656f41..08798c56dcce 100644
--- a/drivers/mmc/core/block.h
+++ b/drivers/mmc/core/block.h
@@ -17,4 +17,8 @@ struct work_struct;
 
 void mmc_blk_mq_complete_work(struct work_struct *work);
 
+/* MMC block device helper for mmcpstore */
+struct mmc_card;
+struct mmc_card *mmc_blk_get_card_by_name(const char *device_name);
+
 #endif
-- 
2.34.1