mtd: spinand: Constify struct nand_ecc_engine_ops

'struct nand_ecc_engine_ops' are not modified in these drivers.

Constifying this structure moves some data to a read-only section, so
increases overall security, especially when the structure holds some
function pointers.

Update the prototype of mxic_ecc_get_pipelined_ops() accordingly.

On a x86_64, with allmodconfig, as an example:
Before:
======
text data bss dec hex filename
16709 1374 16 18099 46b3 drivers/mtd/nand/ecc-mxic.o

After:
=====
text data bss dec hex filename
16789 1294 16 18099 46b3 drivers/mtd/nand/ecc-mxic.o

Signed-off-by: Christophe JAILLET <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/72597e9de2[e-mail]

drivers/mtd/nand/ecc-mxic.c

···
 	return ret;
 }
 
-static struct nand_ecc_engine_ops mxic_ecc_engine_external_ops = {
+static const struct nand_ecc_engine_ops mxic_ecc_engine_external_ops = {
 	.init_ctx = mxic_ecc_init_ctx_external,
 	.cleanup_ctx = mxic_ecc_cleanup_ctx,
 	.prepare_io_req = mxic_ecc_prepare_io_req_external,
 	.finish_io_req = mxic_ecc_finish_io_req_external,
 };
 
-static struct nand_ecc_engine_ops mxic_ecc_engine_pipelined_ops = {
+static const struct nand_ecc_engine_ops mxic_ecc_engine_pipelined_ops = {
 	.init_ctx = mxic_ecc_init_ctx_pipelined,
 	.cleanup_ctx = mxic_ecc_cleanup_ctx,
 	.prepare_io_req = mxic_ecc_prepare_io_req_pipelined,
 	.finish_io_req = mxic_ecc_finish_io_req_pipelined,
 };
 
-struct nand_ecc_engine_ops *mxic_ecc_get_pipelined_ops(void)
+const struct nand_ecc_engine_ops *mxic_ecc_get_pipelined_ops(void)
 {
 	return &mxic_ecc_engine_pipelined_ops;
 }

drivers/mtd/nand/ecc-sw-bch.c

···
 	return max_bitflips;
 }
 
-static struct nand_ecc_engine_ops nand_ecc_sw_bch_engine_ops = {
+static const struct nand_ecc_engine_ops nand_ecc_sw_bch_engine_ops = {
 	.init_ctx = nand_ecc_sw_bch_init_ctx,
 	.cleanup_ctx = nand_ecc_sw_bch_cleanup_ctx,
 	.prepare_io_req = nand_ecc_sw_bch_prepare_io_req,

drivers/mtd/nand/ecc-sw-hamming.c

···
 	return max_bitflips;
 }
 
-static struct nand_ecc_engine_ops nand_ecc_sw_hamming_engine_ops = {
+static const struct nand_ecc_engine_ops nand_ecc_sw_hamming_engine_ops = {
 	.init_ctx = nand_ecc_sw_hamming_init_ctx,
 	.cleanup_ctx = nand_ecc_sw_hamming_cleanup_ctx,
 	.prepare_io_req = nand_ecc_sw_hamming_prepare_io_req,

drivers/mtd/nand/spi/core.c

···
 	return ret;
 }
 
-static struct nand_ecc_engine_ops spinand_ondie_ecc_engine_ops = {
+static const struct nand_ecc_engine_ops spinand_ondie_ecc_engine_ops = {
 	.init_ctx = spinand_ondie_ecc_init_ctx,
 	.cleanup_ctx = spinand_ondie_ecc_cleanup_ctx,
 	.prepare_io_req = spinand_ondie_ecc_prepare_io_req,

drivers/spi/spi-mtk-snfi.c

···
 	return snf->ecc_stats.failed ? -EBADMSG : snf->ecc_stats.bitflips;
 }
 
-static struct nand_ecc_engine_ops mtk_snfi_ecc_engine_ops = {
+static const struct nand_ecc_engine_ops mtk_snfi_ecc_engine_ops = {
 	.init_ctx = mtk_snand_ecc_init_ctx,
 	.cleanup_ctx = mtk_snand_ecc_cleanup_ctx,
 	.prepare_io_req = mtk_snand_ecc_prepare_io_req,

drivers/spi/spi-mxic.c

···
 /* ECC wrapper */
 static int mxic_spi_mem_ecc_init_ctx(struct nand_device *nand)
 {
-	struct nand_ecc_engine_ops *ops = mxic_ecc_get_pipelined_ops();
+	const struct nand_ecc_engine_ops *ops = mxic_ecc_get_pipelined_ops();
 	struct mxic_spi *mxic = nand->ecc.engine->priv;
 
 	mxic->ecc.use_pipelined_conf = true;
···
 
 static void mxic_spi_mem_ecc_cleanup_ctx(struct nand_device *nand)
 {
-	struct nand_ecc_engine_ops *ops = mxic_ecc_get_pipelined_ops();
+	const struct nand_ecc_engine_ops *ops = mxic_ecc_get_pipelined_ops();
 	struct mxic_spi *mxic = nand->ecc.engine->priv;
 
 	mxic->ecc.use_pipelined_conf = false;
···
 static int mxic_spi_mem_ecc_prepare_io_req(struct nand_device *nand,
 					   struct nand_page_io_req *req)
 {
-	struct nand_ecc_engine_ops *ops = mxic_ecc_get_pipelined_ops();
+	const struct nand_ecc_engine_ops *ops = mxic_ecc_get_pipelined_ops();
 
 	return ops->prepare_io_req(nand, req);
 }
···
 static int mxic_spi_mem_ecc_finish_io_req(struct nand_device *nand,
 					  struct nand_page_io_req *req)
 {
-	struct nand_ecc_engine_ops *ops = mxic_ecc_get_pipelined_ops();
+	const struct nand_ecc_engine_ops *ops = mxic_ecc_get_pipelined_ops();
 
 	return ops->finish_io_req(nand, req);
 }
 
-static struct nand_ecc_engine_ops mxic_spi_mem_ecc_engine_pipelined_ops = {
+static const struct nand_ecc_engine_ops mxic_spi_mem_ecc_engine_pipelined_ops = {
 	.init_ctx = mxic_spi_mem_ecc_init_ctx,
 	.cleanup_ctx = mxic_spi_mem_ecc_cleanup_ctx,
 	.prepare_io_req = mxic_spi_mem_ecc_prepare_io_req,

include/linux/mtd/nand-ecc-mxic.h

···
 
 #if IS_ENABLED(CONFIG_MTD_NAND_ECC_MXIC) && IS_REACHABLE(CONFIG_MTD_NAND_CORE)
 
-struct nand_ecc_engine_ops *mxic_ecc_get_pipelined_ops(void);
+const struct nand_ecc_engine_ops *mxic_ecc_get_pipelined_ops(void);
 struct nand_ecc_engine *mxic_ecc_get_pipelined_engine(struct platform_device *spi_pdev);
 void mxic_ecc_put_pipelined_engine(struct nand_ecc_engine *eng);
 int mxic_ecc_process_data_pipelined(struct nand_ecc_engine *eng,
···
 
 #else /* !CONFIG_MTD_NAND_ECC_MXIC */
 
-static inline struct nand_ecc_engine_ops *mxic_ecc_get_pipelined_ops(void)
+static inline const struct nand_ecc_engine_ops *mxic_ecc_get_pipelined_ops(void)
 {
 	return NULL;
 }

include/linux/mtd/nand.h

···
 struct nand_ecc_engine {
 	struct device *dev;
 	struct list_head node;
-	struct nand_ecc_engine_ops *ops;
+	const struct nand_ecc_engine_ops *ops;
 	enum nand_ecc_engine_integration integration;
 	void *priv;
 };