Hi Huang,
I've added some code comments inline (and I'll squash them in my next
version).
On Tue, 23 Sep 2014 16:07:34 +0200
Boris BREZILLON <boris.brezil...@free-electrons.com> wrote:
> Add a new function to move bits (not bytes) from a memory region to
> another one.
> This function is similar to memmove except it acts at bit level.
> This function is needed to implement GPMI raw access functions, given the
> fact that ECC engine does not pad ECC bits to the next byte boundary.
>
> Signed-off-by: Boris BREZILLON <boris.brezil...@free-electrons.com>
> ---
> drivers/mtd/nand/gpmi-nand/gpmi-lib.c | 88
> ++++++++++++++++++++++++++++++++++
> drivers/mtd/nand/gpmi-nand/gpmi-nand.h | 4 ++
> 2 files changed, 92 insertions(+)
>
> diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> b/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> index 87e658c..e2f706a 100644
> --- a/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> +++ b/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> @@ -1353,3 +1353,91 @@ int gpmi_read_page(struct gpmi_nand_data *this,
> set_dma_type(this, DMA_FOR_READ_ECC_PAGE);
> return start_dma_with_bch_irq(this, desc);
> }
> +
> +void gpmi_move_bits(u8 *dst, size_t dst_bit_off,
> + const u8 *src, size_t src_bit_off,
> + size_t nbits)
> +{
> + size_t i;
> + size_t nbytes;
> + u32 src_byte = 0;
> +
/*
* Move src and dst pointers to the closest byte pointer and
* store bit offsets within a byte.
*/
> + src += src_bit_off / 8;
> + src_bit_off %= 8;
> +
> + dst += dst_bit_off / 8;
> + dst_bit_off %= 8;
> +
/*
* Initialize the src_byte value with bits available in the
* first byte of data so that we end up with a byte aligned
* src pointer.
*/
> + if (src_bit_off) {
> + src_byte = src[0] >> src_bit_off;
> + nbits -= 8 - src_bit_off;
> + src++;
> + }
> +
/*
* Calculate the number of bytes that can be copied from src to
* dst.
*/
> + nbytes = nbits / 8;
> +
/*
* Try to align dst to a byte boundary by peeking some bits
* from the source.
*/
> + if (dst_bit_off) {
> + if (src_bit_off <= dst_bit_off) {
> + dst[0] &= GENMASK(dst_bit_off - 1, 0);
> + dst[0] |= src_byte << dst_bit_off;
> + src_bit_off += (8 - dst_bit_off);
> + src_byte >>= (8 - dst_bit_off);
> + dst_bit_off = 0;
> + dst++;
> + } else if (nbytes) {
> + src_byte |= src[0] << (8 - src_bit_off);
> + dst[0] &= GENMASK(dst_bit_off - 1, 0);
> + dst[0] |= src_byte << dst_bit_off;
> + src_bit_off += dst_bit_off;
> + src_byte >>= (8 - dst_bit_off);
> + dst_bit_off = 0;
> + dst++;
> + nbytes--;
> + src++;
> + if (src_bit_off > 7) {
> + src_bit_off -= 8;
> + dst[0] = src_byte;
> + dst++;
> + src_byte >>= 8;
> + }
> + }
> + }
> +
> + if (!src_bit_off && !dst_bit_off) {
/*
* Both src and dst pointers are byte aligned, thus we
* can just use the optimized memcpy function
*/
> + if (nbytes)
> + memcpy(dst, src, nbytes);
> + } else {
/*
* src buffer is not byte aligned, hence we have to copy
* each src byte to the src_byte variable (after
* applying the appropriate shift depending on the
* src bit offset).
* We still try to work on bytes until there's not
* enough available data in the src buffer.
*/
> + for (i = 0; i < nbytes; i++) {
> + src_byte |= src[i] << (8 - src_bit_off);
> + dst[i] = src_byte;
> + src_byte >>= 8;
> + }
> + }
> +
/* move dst and src buffers */
> + dst += nbytes;
> + src += nbytes;
/*
* nbits is the number of remaining bits. It should not exceed
* 8 as we've already worked on bytes as much as possible.
*/
> + nbits %= 8;
> +
/*
* if there's no more bits to copy to the destination and src
* buffer was already byte aligned, then we're done.
*/
> + if (!nbits && !src_bit_off)
> + return;
> +
/* Copy the remaining bits to the src_byte variable */
> + if (nbits)
> + src_byte |= (*src & GENMASK(nbits - 1, 0)) <<
> + ((8 - src_bit_off) % 8);
> + nbits += (8 - src_bit_off) % 8;
> +
/*
* There were not enough bits to copy from src to dst to get a
* byte aligned dst buffer. In this case prepare the src_byte
* variable to match the dst organization (just shift src_byte
* by dst bit offset and retrieve least significant bits from
* dst).
*/
> + if (dst_bit_off)
> + src_byte = (src_byte << dst_bit_off) |
> + (*dst & GENMASK(dst_bit_off - 1, 0));
> + nbits += dst_bit_off;
> +
/*
* Keep most significant bits from dst if we end up with an
* unaligned number bits.
*/
> + if (nbits % 8)
> + src_byte |= (dst[nbits / 8] & GENMASK(7, nbits % 8)) <<
> + (nbits / 8);
> +
/* Copy the remaining bytes to the destination */
> + nbytes = DIV_ROUND_UP(nbits, 8);
> + for (i = 0; i < nbytes; i++) {
> + dst[i] = src_byte;
> + src_byte >>= 8;
> + }
> +}
> diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-nand.h
> b/drivers/mtd/nand/gpmi-nand/gpmi-nand.h
> index 32c6ba4..17d0736 100644
> --- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.h
> +++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.h
> @@ -290,6 +290,10 @@ extern int gpmi_send_page(struct gpmi_nand_data *,
> extern int gpmi_read_page(struct gpmi_nand_data *,
> dma_addr_t payload, dma_addr_t auxiliary);
>
> +void gpmi_move_bits(u8 *dst, size_t dst_bit_off,
> + const u8 *src, size_t src_bit_off,
> + size_t nbits);
> +
> /* BCH : Status Block Completion Codes */
> #define STATUS_GOOD 0x00
> #define STATUS_ERASED 0xff
--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
