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    SubjectRe: [PATCH v3 5/7] mtd: rawnand: ams-delta: Set port direction when needed
    On Tue, 14 Aug 2018 00:34:46 +0200
    Janusz Krzysztofik <jmkrzyszt@gmail.com> wrote:

    > In its current shape, the driver sets data port direction before each
    > byte read/write operation, even during multi-byte transfers. Improve
    > performance of the driver by setting the port direction only when
    > needed.
    >
    > This optimisation will become particularly important as soon as
    > planned conversion of the driver to GPIO API for data I/O will be
    > implemented.
    >
    > Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
    > ---
    > drivers/mtd/nand/raw/ams-delta.c | 59 ++++++++++++++++++++++++++++++++--------
    > 1 file changed, 47 insertions(+), 12 deletions(-)
    >
    > diff --git a/drivers/mtd/nand/raw/ams-delta.c b/drivers/mtd/nand/raw/ams-delta.c
    > index 09d6901fc94d..5f9180fe4f8b 100644
    > --- a/drivers/mtd/nand/raw/ams-delta.c
    > +++ b/drivers/mtd/nand/raw/ams-delta.c
    > @@ -45,6 +45,7 @@ struct ams_delta_nand {
    > struct gpio_desc *gpiod_ale;
    > struct gpio_desc *gpiod_cle;
    > void __iomem *io_base;
    > + bool data_in;
    > };
    >
    > /*
    > @@ -72,50 +73,83 @@ static const struct mtd_partition partition_info[] = {
    > .size = 3 * SZ_256K },
    > };
    >
    > -static void ams_delta_write_byte(struct mtd_info *mtd, u_char byte)
    > +static void ams_delta_write_next_byte(struct mtd_info *mtd, u_char byte)
    > {
    > struct nand_chip *this = mtd_to_nand(mtd);
    > struct ams_delta_nand *priv = nand_get_controller_data(this);
    > - void __iomem *io_base = priv->io_base;
    >
    > - writew(0, io_base + OMAP_MPUIO_IO_CNTL);
    > writew(byte, this->IO_ADDR_W);
    > +
    > gpiod_set_value(priv->gpiod_nwe, 0);
    > ndelay(40);
    > gpiod_set_value(priv->gpiod_nwe, 1);
    > }
    >
    > -static u_char ams_delta_read_byte(struct mtd_info *mtd)
    > +static void ams_delta_write_byte(struct mtd_info *mtd, u_char byte)
    > {
    > - u_char res;
    > struct nand_chip *this = mtd_to_nand(mtd);
    > struct ams_delta_nand *priv = nand_get_controller_data(this);
    > void __iomem *io_base = priv->io_base;
    >
    > + if (priv->data_in) {
    > + writew(0, io_base + OMAP_MPUIO_IO_CNTL);
    > + priv->data_in = false;
    > + }
    > +
    > + ams_delta_write_next_byte(mtd, byte);
    > +}

    I'm not a big fan of this {read,write}_byte/next_byte() approach.

    Can't we do something like:

    static void ams_delta_io_write(struct ams_delta_nand *priv, u8 data)
    {
    writew(byte, priv->nand_chip.IO_ADDR_W);
    gpiod_set_value(priv->gpiod_nwe, 0);
    ndelay(40);
    gpiod_set_value(priv->gpiod_nwe, 1);
    }

    static u8 ams_delta_io_read(struct ams_delta_nand *priv)
    {
    u8 res;

    gpiod_set_value(priv->gpiod_nre, 0);
    ndelay(40);
    res = readw(priv->nand_chip.IO_ADDR_R);
    gpiod_set_value(priv->gpiod_nre, 1);

    return res;
    }

    static void ams_delta_set_io_dir(struct ams_delta_nand *priv, bool in)
    {
    if (in == priv->data_in)
    return;

    writew(in ? ~0 : 0, priv->io_base + OMAP_MPUIO_IO_CNTL);
    priv->data_in = in;
    }

    static void ams_delta_write_buf(struct mtd_info *mtd, const u8 *buf,
    int len)
    {
    struct nand_chip *this = mtd_to_nand(mtd);
    struct ams_delta_nand *priv = nand_get_controller_data(this);
    int i;

    ams_delta_set_io_dir(priv, false);

    for (i =0; i < len; i++)
    ams_delta_io_write(priv, buf[i]);
    }

    static void ams_delta_write_byte(struct mtd_info *mtd, u8 byte)
    {
    ams_delta_write_buf(mtd, &byte, 1);
    }

    static void ams_delta_read_buf(struct mtd_info *mtd, u8 *buf, int len)
    {
    struct nand_chip *this = mtd_to_nand(mtd);
    struct ams_delta_nand *priv = nand_get_controller_data(this);
    int i;

    ams_delta_set_io_dir(priv, true);

    for (i = 0; i < len; i++)
    buf[i] = ams_delta_io_read(priv);
    }

    static u8 ams_delta_read_byte(struct mtd_info *mtd)
    {
    u8 res;

    ams_delta_read_buf(mtd, &res, 1);

    return res;
    }

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