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    SubjectRe: [RFC PATCH v2 07/12] mtd: rawnand: ams-delta: Set port direction once per transfer
    On Tue,  7 Aug 2018 00:29:13 +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. Since
    > performance of the driver is completely not acceptable on Amstrad Delta
    > after it has been converted to GPIO bitbang, try to improve things a
    > bit by setting the port direction only on first byte of each transfer.
    >
    > Resulting performance on Amstrad Delta is still far from acceptable.
    >
    > Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
    > ---
    > drivers/mtd/nand/raw/ams-delta.c | 58 ++++++++++++++++++++++++++++++++--------
    > 1 file changed, 47 insertions(+), 11 deletions(-)
    >
    > diff --git a/drivers/mtd/nand/raw/ams-delta.c b/drivers/mtd/nand/raw/ams-delta.c
    > index 78996ddf82e0..d02c48c013e8 100644
    > --- a/drivers/mtd/nand/raw/ams-delta.c
    > +++ b/drivers/mtd/nand/raw/ams-delta.c
    > @@ -69,6 +69,30 @@ static const struct mtd_partition partition_info[] = {
    > .size = 3 * SZ_256K },
    > };
    >
    > +static void ams_delta_write_commit(struct ams_delta_nand *priv)
    > +{
    > + gpiod_set_value(priv->gpiod_nwe, 0);
    > + ndelay(40);
    > + gpiod_set_value(priv->gpiod_nwe, 1);
    > +}
    > +
    > +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);
    > + struct gpio_descs *data_gpiods = priv->data_gpiods;
    > + unsigned long bits = byte;
    > + int i, value_array[data_gpiods->ndescs];
    > +
    > + for (i = 0; i < data_gpiods->ndescs; i++)
    > + value_array[i] = test_bit(i, &bits);
    > +
    > + gpiod_set_raw_array_value(data_gpiods->ndescs, data_gpiods->desc,
    > + value_array);
    > +
    > + ams_delta_write_commit(priv);
    > +}
    > +
    > static void ams_delta_write_byte(struct mtd_info *mtd, u_char byte)
    > {
    > struct nand_chip *this = mtd_to_nand(mtd);
    > @@ -81,12 +105,10 @@ static void ams_delta_write_byte(struct mtd_info *mtd, u_char byte)
    > gpiod_direction_output_raw(data_gpiods->desc[i],
    > test_bit(i, &bits));
    >
    > - gpiod_set_value(priv->gpiod_nwe, 0);
    > - ndelay(40);
    > - gpiod_set_value(priv->gpiod_nwe, 1);
    > + ams_delta_write_commit(priv);
    > }
    >
    > -static u_char ams_delta_read_byte(struct mtd_info *mtd)
    > +static u_char ams_delta_read_next_byte(struct mtd_info *mtd)
    > {
    > struct nand_chip *this = mtd_to_nand(mtd);
    > struct ams_delta_nand *priv = nand_get_controller_data(this);
    > @@ -94,9 +116,6 @@ static u_char ams_delta_read_byte(struct mtd_info *mtd)
    > unsigned long bits = 0;
    > int i, value_array[data_gpiods->ndescs];
    >
    > - for (i = 0; i < data_gpiods->ndescs; i++)
    > - gpiod_direction_input(data_gpiods->desc[i]);
    > -
    > gpiod_set_value(priv->gpiod_nre, 0);
    > ndelay(40);
    >
    > @@ -112,21 +131,38 @@ static u_char ams_delta_read_byte(struct mtd_info *mtd)
    > return bits;
    > }
    >
    > +static u_char ams_delta_read_byte(struct mtd_info *mtd)
    > +{
    > + struct nand_chip *this = mtd_to_nand(mtd);
    > + struct ams_delta_nand *priv = nand_get_controller_data(this);
    > + struct gpio_descs *data_gpiods = priv->data_gpiods;
    > + int i;
    > +
    > + for (i = 0; i < data_gpiods->ndescs; i++)
    > + gpiod_direction_input(data_gpiods->desc[i]);
    > +
    > + return ams_delta_read_next_byte(mtd);
    > +}
    > +
    > static void ams_delta_write_buf(struct mtd_info *mtd, const u_char *buf,
    > int len)
    > {
    > int i;
    >
    > - for (i=0; i<len; i++)
    > - ams_delta_write_byte(mtd, buf[i]);
    > + if (len > 0)
    > + ams_delta_write_byte(mtd, buf[0]);
    > + for (i = 1; i < len; i++)
    > + ams_delta_write_next_byte(mtd, buf[i]);
    > }
    >
    > static void ams_delta_read_buf(struct mtd_info *mtd, u_char *buf, int len)
    > {
    > int i;
    >
    > - for (i=0; i<len; i++)
    > - buf[i] = ams_delta_read_byte(mtd);
    > + if (len > 0)
    > + buf[0] = ams_delta_read_byte(mtd);
    > + for (i = 1; i < len; i++)
    > + buf[i] = ams_delta_read_next_byte(mtd);
    > }

    I'd suggest a slightly different approach where the data pins
    direction state is stored in the the priv struct and only changed when
    required. This way you just have to add a test in
    ams_delta_read/write_byte().

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