On 09/01/2025 04:35, Dmitry Baryshkov wrote:
If the NVMEM specifies a stride to access data, reading particular cell
might require bit offset that is bigger than one byte. Rework NVMEM core
code to support bit offsets of more than 8 bits.
If the plan is to support bit offset above 8 bits, please update
./Documentation/devicetree/bindings/nvmem/layouts/fixed-cell.yaml to
reflect this too.
--srini
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
---
drivers/nvmem/core.c | 24 +++++++++++++++++-------
1 file changed, 17 insertions(+), 7 deletions(-)
diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index d6494dfc20a7324bde6415776dcabbb0bfdd334b..7fa85b0804db360035d7471002dbf79658d5830b 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -834,7 +834,9 @@ static int nvmem_add_cells_from_dt(struct nvmem_device *nvmem, struct device_nod
if (addr && len == (2 * sizeof(u32))) {
info.bit_offset = be32_to_cpup(addr++);
info.nbits = be32_to_cpup(addr);
- if (info.bit_offset >= BITS_PER_BYTE || info.nbits < 1) {
+ if (info.bit_offset >= BITS_PER_BYTE * info.bytes ||
+ info.nbits < 1 ||
+ info.bit_offset + info.nbits > BITS_PER_BYTE * info.bytes) {
dev_err(dev, "nvmem: invalid bits on %pOF\n", child);
of_node_put(child);
return -EINVAL;
@@ -1627,21 +1629,29 @@ 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, extra, bytes_offset;
+ int bit_offset = cell->bit_offset;
p = b = buf;
- if (bit_offset) {
+
+ bytes_offset = bit_offset / BITS_PER_BYTE;
+ b += bytes_offset;
+ bit_offset %= BITS_PER_BYTE;
+
+ if (bit_offset % BITS_PER_BYTE) {
/* First shift */
- *b++ >>= bit_offset;
+ *p = *b++ >> bit_offset;
/* setup rest of the bytes if any */
for (i = 1; i < cell->bytes; i++) {
/* Get bits from next byte and shift them towards msb */
- *p |= *b << (BITS_PER_BYTE - bit_offset);
+ *p++ |= *b << (BITS_PER_BYTE - bit_offset);
- p = b;
- *b++ >>= bit_offset;
+ *p = *b++ >> bit_offset;
}
+ } else if (p != b) {
+ memmove(p, b, cell->bytes - bytes_offset);
+ p += cell->bytes - 1;
} else {
/* point to the msb */
p += cell->bytes - 1;
