mtd: nand: ecc: Provide a helper to retrieve a pilelined engine device

In a pipelined engine situation, we might either have the host which
internally has support for error correction, or have it using an
external hardware block for this purpose. In the former case, the host
is also the ECC engine. In the latter case, it is not. In order to get
the right pointers on the right devices (for example: in order to devm_*
allocate variables), let's introduce this helper which can safely be
called by pipelined ECC engines in order to retrieve the right device
structure.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20211216111654.238086-16-miquel.raynal@bootlin.com

drivers/mtd/nand/ecc.c

@@ -699,6 +699,37 @@ void nand_ecc_put_on_host_hw_engine(struct nand_device *nand)
 }
 EXPORT_SYMBOL(nand_ecc_put_on_host_hw_engine);
 
+/*
+ * In the case of a pipelined engine, the device registering the ECC
+ * engine is not necessarily the ECC engine itself but may be a host controller.
+ * It is then useful to provide a helper to retrieve the right device object
+ * which actually represents the ECC engine.
+ */
+struct device *nand_ecc_get_engine_dev(struct device *host)
+{
+	struct platform_device *ecc_pdev;
+	struct device_node *np;
+
+	/*
+	 * If the device node contains this property, it means we need to follow
+	 * it in order to get the right ECC engine device we are looking for.
+	 */
+	np = of_parse_phandle(host->of_node, "nand-ecc-engine", 0);
+	if (!np)
+		return host;
+
+	ecc_pdev = of_find_device_by_node(np);
+	if (!ecc_pdev) {
+		of_node_put(np);
+		return NULL;
+	}
+
+	platform_device_put(ecc_pdev);
+	of_node_put(np);
+
+	return &ecc_pdev->dev;
+}
+
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Miquel Raynal <miquel.raynal@bootlin.com>");
 MODULE_DESCRIPTION("Generic ECC engine");

include/linux/mtd/nand.h

@@ -309,6 +309,7 @@ struct nand_ecc_engine *nand_ecc_get_sw_engine(struct nand_device *nand);
 struct nand_ecc_engine *nand_ecc_get_on_die_hw_engine(struct nand_device *nand);
 struct nand_ecc_engine *nand_ecc_get_on_host_hw_engine(struct nand_device *nand);
 void nand_ecc_put_on_host_hw_engine(struct nand_device *nand);
+struct device *nand_ecc_get_engine_dev(struct device *host);
 
 #if IS_ENABLED(CONFIG_MTD_NAND_ECC_SW_HAMMING)
 struct nand_ecc_engine *nand_ecc_sw_hamming_get_engine(void);