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Message-ID: <20141126175708.1acb90ac@bbrezillon>
Date: Wed, 26 Nov 2014 17:57:08 +0100
From: Boris Brezillon <boris.brezillon@...e-electrons.com>
To: Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc: David Woodhouse <dwmw2@...radead.org>,
Brian Norris <computersforpeace@...il.com>,
linux-mtd@...ts.infradead.org, Huang Shijie <shijie8@...il.com>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
Mike Voytovich <mvoytovich@...pal.com>,
Roy Lee <roylee@...pal.com>
Subject: Re: [PATCH v5 1/3] mtd: nand: gpmi: add gpmi_move_bits function
On Wed, 26 Nov 2014 17:53:11 +0100
Boris Brezillon <boris.brezillon@...e-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.brezillon@...e-electrons.com>
> ---
> drivers/mtd/nand/gpmi-nand/gpmi-lib.c | 151 +++++++++++++++++++++++++++++++++
> drivers/mtd/nand/gpmi-nand/gpmi-nand.h | 4 +
> 2 files changed, 155 insertions(+)
>
> diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-lib.c b/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> index 87e658c..77eff0e 100644
> --- a/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> +++ b/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> @@ -1353,3 +1353,154 @@ 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);
> }
> +
> +/**
> + * gpmi_move_bits - move bits from one memory region to another
> + * @dst: destination buffer
> + * @dst_bit_off: bit offset we're starting to write at
> + * @src: source buffer
> + * @src_bit_off: bit offset we're starting to read from
> + * @nbits: number of bits to copy
> + *
> + * This functions copies bits from one memory region to another, and is used by
> + * the GPMI driver to copy ECC sections which are not guaranteed to be byte
> + * aligned.
I forgot to add that src and dst should not overlap, otherwise it won't
work...
> + *
> + */
> +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_buffer = 0;
> + size_t bits_in_src_buffer = 0;
> +
> + if (!nbits)
> + return;
> +
> + /*
> + * 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_buffer 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_buffer = src[0] >> src_bit_off;
> + if (nbits >= (8 - src_bit_off)) {
> + bits_in_src_buffer += 8 - src_bit_off;
> + } else {
> + src_buffer &= GENMASK(nbits - 1, 0);
> + bits_in_src_buffer += nbits;
> + }
> + nbits -= bits_in_src_buffer;
> + 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. */
> + if (dst_bit_off) {
> + if (bits_in_src_buffer < (8 - dst_bit_off) && nbytes) {
> + src_buffer |= src[0] << bits_in_src_buffer;
> + bits_in_src_buffer += 8;
> + src++;
> + nbytes--;
> + }
> +
> + if (bits_in_src_buffer >= (8 - dst_bit_off)) {
> + dst[0] &= GENMASK(dst_bit_off - 1, 0);
> + dst[0] |= src_buffer << dst_bit_off;
> + src_buffer >>= (8 - dst_bit_off);
> + bits_in_src_buffer -= (8 - dst_bit_off);
> + dst_bit_off = 0;
> + dst++;
> + if (bits_in_src_buffer > 7) {
> + bits_in_src_buffer -= 8;
> + dst[0] = src_buffer;
> + dst++;
> + src_buffer >>= 8;
> + }
> + }
> + }
> +
> + if (!bits_in_src_buffer && !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_buffer variable before extracting a byte
> + * to store in dst.
> + */
> + for (i = 0; i < nbytes; i++) {
> + src_buffer |= src[i] << bits_in_src_buffer;
> + dst[i] = src_buffer;
> + src_buffer >>= 8;
> + }
> + }
> + /* Update dst and src pointers */
> + dst += nbytes;
> + src += nbytes;
> +
> + /*
> + * nbits is the number of remaining bits. It should not exceed 8 as
> + * we've already copied as much bytes 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 && !bits_in_src_buffer)
> + return;
> +
> + /* Copy the remaining bits to src_buffer */
> + if (nbits)
> + src_buffer |= (*src & GENMASK(nbits - 1, 0)) <<
> + bits_in_src_buffer;
> + bits_in_src_buffer += nbits;
> +
> + /*
> + * In case there were not enough bits to get a byte aligned dst buffer
> + * prepare the src_buffer variable to match the dst organization (shift
> + * src_buffer by dst_bit_off and retrieve the least significant bits
> + * from dst).
> + */
> + if (dst_bit_off)
> + src_buffer = (src_buffer << dst_bit_off) |
> + (*dst & GENMASK(dst_bit_off - 1, 0));
> + bits_in_src_buffer += dst_bit_off;
> +
> + /*
> + * Keep most significant bits from dst if we end up with an unaligned
> + * number of bits.
> + */
> + nbytes = bits_in_src_buffer / 8;
> + if (bits_in_src_buffer % 8) {
> + src_buffer |= (dst[nbytes] &
> + GENMASK(7, bits_in_src_buffer % 8)) <<
> + (nbytes * 8);
> + nbytes++;
> + }
> +
> + /* Copy the remaining bytes to dst */
> + for (i = 0; i < nbytes; i++) {
> + dst[i] = src_buffer;
> + src_buffer >>= 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
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