[PATCH 1/7] nvmem: core: allow bit offset > 8

[Sven Peter via B4 Relay <devnull+sven.svenpeter.dev@kernel.org>]

From: Sven Peter <sven@svenpeter.dev>

Some nvmem controllers like Apple's eFuses or Nintendo's OTP have a cell
size that's larger than one byte. Consumers may however still need
access to a subset of bits that start after the first byte.

Signed-off-by: Sven Peter <sven@svenpeter.dev>
---
 drivers/nvmem/core.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index fff85bbf0ecd0f638e21f127370105d9f79c00d2..1bd39b12c21a86b9b135be95251a52a10543c2ea 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -1630,15 +1630,24 @@ EXPORT_SYMBOL_GPL(nvmem_cell_put);
 static void nvmem_shift_read_buffer_in_place(struct nvmem_cell_entry *cell, void *buf)
 {
 	u8 *p, *b;
-	int i, extra, bit_offset = cell->bit_offset;
+	int i, padding, extra, bit_offset = cell->bit_offset;
+	int bytes = cell->bytes;
 
 	p = b = buf;
 	if (bit_offset) {
+		/* Remove any full bytes at the beginning that contain no bits of interest */
+		padding = bit_offset / BITS_PER_BYTE;
+		if (padding) {
+			memmove(buf, buf + padding, bytes - padding);
+			bit_offset -= BITS_PER_BYTE * padding;
+			bytes -= padding;
+		}
+
 		/* First shift */
 		*b++ >>= bit_offset;
 
 		/* setup rest of the bytes if any */
-		for (i = 1; i < cell->bytes; i++) {
+		for (i = 1; i < bytes; i++) {
 			/* Get bits from next byte and shift them towards msb */
 			*p |= *b << (BITS_PER_BYTE - bit_offset);
 
@@ -1651,7 +1660,7 @@ static void nvmem_shift_read_buffer_in_place(struct nvmem_cell_entry *cell, void
 	}
 
 	/* result fits in less bytes */
-	extra = cell->bytes - DIV_ROUND_UP(cell->nbits, BITS_PER_BYTE);
+	extra = bytes - DIV_ROUND_UP(cell->nbits, BITS_PER_BYTE);
 	while (--extra >= 0)
 		*p-- = 0;
 

-- 
2.34.1