[PATCH] nvmem: core: Allow sub-register width nvmem_regmap_write()

From: Ahmad Fatoum <[email protected]>

The previous implementation of nvmem_regmap_write() required the
supplied value to be a multiple of the register size defined by the
driver ("expect users to observe alignment").

This is however not respected by nvmem cell functions
nvmem_cell_prepare_write_buffer()/__nvmem_cell_entry_write() which
prepare the value buffer based on the "bits" supplied in the devicetree,
resulting in EINVAL errors if an nvmem cell with "bits" spanning less
bytes than val_bytes = DIV_ROUND_UP(config->val_bits, 8) of the nvmem
driver.

To resolve this, accept buffers shorter than val_bytes, and place them
correctly with regard to endianness.

Not-Signed-off-by: Ahmad Fatoum <[email protected]>
Signed-off-by: Jonas Rebmann <[email protected]>
---
Ahmad and me pair-programmed this on friday. Ahmad, can we have your
SoB?
---
 drivers/nvmem/regmap.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/drivers/nvmem/regmap.c b/drivers/nvmem/regmap.c
index 98e57909eb..22e667af17 100644
--- a/drivers/nvmem/regmap.c
+++ b/drivers/nvmem/regmap.c
@@ -12,16 +12,31 @@
 static int nvmem_regmap_write(void *ctx, unsigned offset, const void *val, size_t bytes)
 {
 	struct regmap *map = ctx;
+	unsigned int tmp;
 
-	/*
-	 * eFuse writes going through this function may be irreversible,
-	 * so expect users to observe alignment.
-	 */
-	if (bytes % regmap_get_val_bytes(map))
+	if (bytes > regmap_get_val_bytes(map)) {
+		if (bytes % regmap_get_val_bytes(map))
+			return -EINVAL;
+
+		return regmap_bulk_write(map, offset, val,
+					 bytes / regmap_get_val_bytes(map));
+	}
+
+	switch (bytes) {
+	case 1:
+		tmp = *(u8 *)val;
+		break;
+	case 2:
+		tmp = *(u16 *)val;
+		break;
+	case 4:
+		tmp = *(u32 *)val;
+		break;
+	default:
 		return -EINVAL;
+	}
 
-	return regmap_bulk_write(map, offset, val,
-				 bytes / regmap_get_val_bytes(map));
+	return regmap_write(map, offset, tmp);
 }
 
 static int nvmem_regmap_read(void *ctx, unsigned offset, void *buf, size_t bytes)

---
base-commit: f5956c772dc00837bad36fc66df8a53aae86558d
change-id: 20260525-short_nvmem_write-86a2114f6774

Best regards,
--  
Jonas Rebmann <[email protected]>