mtd: rawnand: Add nand_extract_bits()

There are cases where ECC bytes are not byte-aligned. Indeed, BCH
implies using a number of ECC bits, which are not always a multiple of
8. We then need a helper like nand_extract_bits() to extract these
syndromes from a buffer.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200519074549.23673-5-miquel.raynal@bootlin.com

diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
index 475647ea6948554da681dd40c67408d854e9bf9d..6a6a0a36b3fd59564a6d5735298efea6e3314461 100644 (file)
--- a/drivers/mtd/nand/raw/nand_base.c
+++ b/drivers/mtd/nand/raw/nand_base.c
@@ -274,6 +274,50 @@ static int check_offs_len(struct nand_chip *chip, loff_t ofs, uint64_t len)
        return ret;
 }
 
+/**
+ * nand_extract_bits - Copy unaligned bits from one buffer to another one
+ * @dst: destination buffer
+ * @dst_off: bit offset at which the writing starts
+ * @src: source buffer
+ * @src_off: bit offset at which the reading starts
+ * @nbits: number of bits to copy from @src to @dst
+ *
+ * Copy bits from one memory region to another (overlap authorized).
+ */
+void nand_extract_bits(u8 *dst, unsigned int dst_off, const u8 *src,
+                      unsigned int src_off, unsigned int nbits)
+{
+       unsigned int tmp, n;
+
+       dst += dst_off / 8;
+       dst_off %= 8;
+       src += src_off / 8;
+       src_off %= 8;
+
+       while (nbits) {
+               n = min3(8 - dst_off, 8 - src_off, nbits);
+
+               tmp = (*src >> src_off) & GENMASK(n - 1, 0);
+               *dst &= ~GENMASK(n - 1 + dst_off, dst_off);
+               *dst |= tmp << dst_off;
+
+               dst_off += n;
+               if (dst_off >= 8) {
+                       dst++;
+                       dst_off -= 8;
+               }
+
+               src_off += n;
+               if (src_off >= 8) {
+                       src++;
+                       src_off -= 8;
+               }
+
+               nbits -= n;
+       }
+}
+EXPORT_SYMBOL_GPL(nand_extract_bits);
+
 /**
  * nand_select_target() - Select a NAND target (A.K.A. die)
  * @chip: NAND chip object

diff --git a/include/linux/mtd/rawnand.h b/include/linux/mtd/rawnand.h
index a3bac8824937c3d6354b93a95c12d09e74ecd857..2804c13e56621e030502e9fded600a5167f237c8 100644 (file)
--- a/include/linux/mtd/rawnand.h
+++ b/include/linux/mtd/rawnand.h
@@ -1414,6 +1414,10 @@ int nand_gpio_waitrdy(struct nand_chip *chip, struct gpio_desc *gpiod,
 void nand_select_target(struct nand_chip *chip, unsigned int cs);
 void nand_deselect_target(struct nand_chip *chip);
 
+/* Bitops */
+void nand_extract_bits(u8 *dst, unsigned int dst_off, const u8 *src,
+                      unsigned int src_off, unsigned int nbits);
+
 /**
  * nand_get_data_buf() - Get the internal page buffer
  * @chip: NAND chip object