Re: [PATCH v3 5/7] mtd: rawnand: ams-delta: Set port direction when needed

[Boris Brezillon]

On Tue, 14 Aug 2018 00:34:46 +0200
Janusz Krzysztofik <jmkrzy...@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 <jmkrzy...@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;
}