[PATCH v2 1/2] mtd: rawnand: Fix the nand_read_data_op() early check

[Miquel Raynal]

The nand_read_data_op() operation, which only consists in DATA_IN
cycles, is sadly not supported by all controllers despite being very
basic. The core, for some time, supposed all drivers would support
it. An improvement to this situation for supporting more constrained
controller added a check to verify if the operation was supported before
attempting it by running the function with the check_only boolean set
first, and then possibly falling back to another (possibly slightly less
optimized) alternative.

An even newer addition moved that check very early and probe time, in
order to perform the check only once. The content of the operation was
not so important, as long as the controller driver would tell whether
such operation on the NAND bus would be possible or not. In practice, no
buffer was provided (no fake buffer or whatever) as it is anyway not
relevant for the "check_only" condition. Unfortunately, early in the
function, there is an if statement verifying that the input parameters
are right for normal use, making the early check always unsuccessful.

Fixes: 9f820fc0651c ("mtd: rawnand: Check the data only read pattern only once")
Cc: stable at vger.kernel.org
Reported-by: Alexander Dahl <ada at thorsis.com>
Closes: https://lore.kernel.org/linux-mtd/20240306-shaky-bunion-d28b65ea97d7@thorsis.com/
Reported-by: Steven Seeger <steven.seeger at flightsystems.net>
Closes: https://lore.kernel.org/linux-mtd/DM6PR05MB4506554457CF95191A670BDEF7062@DM6PR05MB4506.namprd05.prod.outlook.com/
Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
Reviewed-by: Alexander Dahl <ada at thorsis.com>
---
 drivers/mtd/nand/raw/nand_base.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
index acd137dd0957..248e654ecefd 100644
--- a/drivers/mtd/nand/raw/nand_base.c
+++ b/drivers/mtd/nand/raw/nand_base.c
@@ -2173,7 +2173,7 @@ EXPORT_SYMBOL_GPL(nand_reset_op);
 int nand_read_data_op(struct nand_chip *chip, void *buf, unsigned int len,
 		      bool force_8bit, bool check_only)
 {
-	if (!len || !buf)
+	if (!len || (!check_only && !buf))
 		return -EINVAL;
 
 	if (nand_has_exec_op(chip)) {
-- 
2.40.1