[PATCH v4] mtd: parsers: ofpart: add workaround for #size-cells 0

[Francesco Dolcini]

From: Francesco Dolcini <francesco.dolcini at toradex.com>

Add a mechanism to handle the case in which partitions are present as
direct child of the nand controller node and #size-cells is set to <0>.

This could happen if the nand-controller node in the DTS is supposed to
have #size-cells set to 0, but for some historical reason/bug it was set
to 1 in the past, and the firmware (e.g. U-Boot) is adding the partition
as direct children of the nand-controller defaulting to #size-cells
being to 1.

This prevents a real boot failure on colibri-imx7 that happened during v6.1
development cycles.

Link: https://lore.kernel.org/all/Y4dgBTGNWpM6SQXI@francesco-nb.int.toradex.com/
Link: https://lore.kernel.org/all/20221202071900.1143950-1-francesco@dolcini.it/
Signed-off-by: Francesco Dolcini <francesco.dolcini at toradex.com>
Reviewed-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
I do not expect this patch to be backported to stable, however I would expect
that we do not backport nand-controller dts cleanups neither.

v4:
 fixed wrong English spelling in the comment

v3:
 minor formatting change, removed not needed new-line and space. 

v2:
 fixup size-cells only when partitions are direct children of the nand-controller
 completely revised commit message, comments and warning print
 use pr_warn instead of pr_warn_once
 added Reviewed-by Greg
 removed cc:stable@ and fixes tag, since the problematic commit was reverted
---
 drivers/mtd/parsers/ofpart_core.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/mtd/parsers/ofpart_core.c b/drivers/mtd/parsers/ofpart_core.c
index 192190c42fc8..e7b8e9d0a910 100644
--- a/drivers/mtd/parsers/ofpart_core.c
+++ b/drivers/mtd/parsers/ofpart_core.c
@@ -122,6 +122,25 @@ static int parse_fixed_partitions(struct mtd_info *master,
 
 		a_cells = of_n_addr_cells(pp);
 		s_cells = of_n_size_cells(pp);
+		if (!dedicated && s_cells == 0) {
+			/*
+			 * This is a ugly workaround to not create
+			 * regression on devices that are still creating
+			 * partitions as direct children of the nand controller.
+			 * This can happen in case the nand controller node has
+			 * #size-cells equal to 0 and the firmware (e.g.
+			 * U-Boot) just add the partitions there assuming
+			 * 32-bit addressing.
+			 *
+			 * If you get this warning your firmware and/or DTS
+			 * should be really fixed.
+			 *
+			 * This is working only for devices smaller than 4GiB.
+			 */
+			pr_warn("%s: ofpart partition %pOF (%pOF) #size-cells is wrongly set to <0>, assuming <1> for parsing partitions.\n",
+				master->name, pp, mtd_node);
+			s_cells = 1;
+		}
 		if (len / 4 != a_cells + s_cells) {
 			pr_debug("%s: ofpart partition %pOF (%pOF) error parsing reg property.\n",
 				 master->name, pp,
-- 
2.25.1