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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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