mtd: rawnand: Constrain even more when continuous reads are enabled

As a matter of fact, continuous reads require additional handling at the
operation level in order for them to work properly. The core helpers do
have this additional logic now, but any time a controller implements its
own page helper, this extra logic is "lost". This means we need another
level of per-controller driver checks to ensure they can leverage
continuous reads. This is for now unsupported, so in order to ensure
continuous reads are enabled only when fully using the core page
helpers, we need to add more initial checks.

Also, as performance is not relevant during raw accesses, we also
prevent these from enabling the feature.

This should solve the issue seen with controllers such as the STM32 FMC2
when in sequencer mode. In this case, the continuous read feature would
be enabled but not leveraged, and most importantly not disabled, leading
to further operations to fail.
Reported-by: Christophe Kerello <christophe.kerello@foss.st.com>
Fixes: 003fe4b9 ("mtd: rawnand: Support for sequential cache reads")
Cc: stable@vger.kernel.org
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Tested-by: Christophe Kerello <christophe.kerello@foss.st.com>
Link: https://lore.kernel.org/linux-mtd/20240307115315.1942678-1-miquel.raynal@bootlin.com

drivers/mtd/nand/raw/nand_base.c

@@ -3594,7 +3594,8 @@ static int nand_do_read_ops(struct nand_chip *chip, loff_t from,
 	oob = ops->oobbuf;
 	oob_required = oob ? 1 : 0;
 
-	rawnand_enable_cont_reads(chip, page, readlen, col);
+	if (likely(ops->mode != MTD_OPS_RAW))
+		rawnand_enable_cont_reads(chip, page, readlen, col);
 
 	while (1) {
 		struct mtd_ecc_stats ecc_stats = mtd->ecc_stats;
@@ -5212,6 +5213,15 @@ static void rawnand_late_check_supported_ops(struct nand_chip *chip)
 	if (!nand_has_exec_op(chip))
 		return;
 
+	/*
+	 * For now, continuous reads can only be used with the core page helpers.
+	 * This can be extended later.
+	 */
+	if (!(chip->ecc.read_page == nand_read_page_hwecc ||
+	      chip->ecc.read_page == nand_read_page_syndrome ||
+	      chip->ecc.read_page == nand_read_page_swecc))
+		return;
+
 	rawnand_check_cont_read_support(chip);
 }