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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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