Subject: [RFC PATCH v2 07/12] mtd: rawnand: ams-delta: Set port direction once per transfer

From: [email-masked] (Boris Brezillon)
Date: Tue, 7 Aug 2018 20:57:52 +0200

On Tue,  7 Aug 2018 00:29:13 +0200
Janusz Krzysztofik <[email-masked]> 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 <[email-masked]>
> ---
>  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().