Re: [PATCH v4 2/3] mtd: spinand: use the spi-mem poll status APIs

[Boris Brezillon <boris.brezillon@collabora.com>]

On Tue, 18 May 2021 15:43:31 +0200
<patrice.chotard@foss.st.com> wrote:

> From: Patrice Chotard <patrice.chotard@foss.st.com>
> 
> Make use of spi-mem poll status APIs to let advanced controllers
> optimize wait operations.
> This should also fix the high CPU usage for system that don't have
> a dedicated STATUS poll block logic.
> 
> Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
> Signed-off-by: Christophe Kerello <christophe.kerello@foss.st.com>
> ---
> Changes in v4:
>   - Update commit message.
>   - Add comment which explains how delays has been calculated.
>   - Rename SPINAND_STATUS_TIMEOUT_MS to SPINAND_WAITRDY_TIMEOUT_MS.
> 
> Changes in v3:
>   - Add initial_delay_us and polling_delay_us parameters to spinand_wait()
>   - Add SPINAND_READ/WRITE/ERASE/RESET_INITIAL_DELAY_US and
>     SPINAND_READ/WRITE/ERASE/RESET_POLL_DELAY_US defines.
> 
> Changes in v2:
>   - non-offload case is now managed by spi_mem_poll_status()
> 
>  drivers/mtd/nand/spi/core.c | 45 ++++++++++++++++++++++++++-----------
>  include/linux/mtd/spinand.h | 22 ++++++++++++++++++
>  2 files changed, 54 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/mtd/nand/spi/core.c b/drivers/mtd/nand/spi/core.c
> index 17f63f95f4a2..3131fae0c715 100644
> --- a/drivers/mtd/nand/spi/core.c
> +++ b/drivers/mtd/nand/spi/core.c
> @@ -473,20 +473,26 @@ static int spinand_erase_op(struct spinand_device *spinand,
>  	return spi_mem_exec_op(spinand->spimem, &op);
>  }
>  
> -static int spinand_wait(struct spinand_device *spinand, u8 *s)
> +static int spinand_wait(struct spinand_device *spinand,
> +			unsigned long initial_delay_us,
> +			unsigned long poll_delay_us,
> +			u8 *s)
>  {
> -	unsigned long timeo =  jiffies + msecs_to_jiffies(400);
> +	struct spi_mem_op op = SPINAND_GET_FEATURE_OP(REG_STATUS,
> +						      spinand->scratchbuf);
>  	u8 status;
>  	int ret;
>  
> -	do {
> -		ret = spinand_read_status(spinand, &status);
> -		if (ret)
> -			return ret;
> +	ret = spi_mem_poll_status(spinand->spimem, &op, STATUS_BUSY, 0,
> +				  initial_delay_us,
> +				  poll_delay_us,
> +				  SPINAND_WAITRDY_TIMEOUT_MS);
> +	if (ret)
> +		return ret;
>  
> -		if (!(status & STATUS_BUSY))
> -			goto out;
> -	} while (time_before(jiffies, timeo));
> +	status = *spinand->scratchbuf;
> +	if (!(status & STATUS_BUSY))
> +		goto out;

Looks like you expect the driver to not only wait for a status change
but also fill the data buffer with the last status value. I think that
should be documented in the SPI mem API.

>  	/*
>  	 * Extra read, just in case the STATUS_READY bit has changed
> @@ -526,7 +532,10 @@ static int spinand_reset_op(struct spinand_device *spinand)
>  	if (ret)
>  		return ret;
>  
> -	return spinand_wait(spinand, NULL);
> +	return spinand_wait(spinand,
> +			    SPINAND_RESET_INITIAL_DELAY_US,
> +			    SPINAND_RESET_POLL_DELAY_US,
> +			    NULL);
>  }
>  
>  static int spinand_lock_block(struct spinand_device *spinand, u8 lock)
> @@ -549,7 +558,10 @@ static int spinand_read_page(struct spinand_device *spinand,
>  	if (ret)
>  		return ret;
>  
> -	ret = spinand_wait(spinand, &status);
> +	ret = spinand_wait(spinand,
> +			   SPINAND_READ_INITIAL_DELAY_US,
> +			   SPINAND_READ_POLL_DELAY_US,
> +			   &status);
>  	if (ret < 0)
>  		return ret;
>  
> @@ -585,7 +597,10 @@ static int spinand_write_page(struct spinand_device *spinand,
>  	if (ret)
>  		return ret;
>  
> -	ret = spinand_wait(spinand, &status);
> +	ret = spinand_wait(spinand,
> +			   SPINAND_WRITE_INITIAL_DELAY_US,
> +			   SPINAND_WRITE_POLL_DELAY_US,
> +			   &status);
>  	if (!ret && (status & STATUS_PROG_FAILED))
>  		return -EIO;
>  
> @@ -768,7 +783,11 @@ static int spinand_erase(struct nand_device *nand, const struct nand_pos *pos)
>  	if (ret)
>  		return ret;
>  
> -	ret = spinand_wait(spinand, &status);
> +	ret = spinand_wait(spinand,
> +			   SPINAND_ERASE_INITIAL_DELAY_US,
> +			   SPINAND_ERASE_POLL_DELAY_US,
> +			   &status);
> +
>  	if (!ret && (status & STATUS_ERASE_FAILED))
>  		ret = -EIO;
>  
> diff --git a/include/linux/mtd/spinand.h b/include/linux/mtd/spinand.h
> index 6bb92f26833e..6988956b8492 100644
> --- a/include/linux/mtd/spinand.h
> +++ b/include/linux/mtd/spinand.h
> @@ -170,6 +170,28 @@ struct spinand_op;
>  struct spinand_device;
>  
>  #define SPINAND_MAX_ID_LEN	4
> +/*
> + * For erase, write and read operation, we got the following timings :
> + * tBERS (erase) 1ms to 4ms
> + * tPROG 300us to 400us
> + * tREAD 25us to 100us
> + * In order to minimize latency, the min value is divided by 4 for the
> + * initial delay, and dividing by 20 for the poll delay.
> + * For reset, 5us/10us/500us if the device is respectively
> + * reading/programming/erasing when the RESET occurs. Since we always
> + * issue a RESET when the device is IDLE, 5us is selected for both initial
> + * and poll delay.
> + */
> +#define SPINAND_READ_INITIAL_DELAY_US	6
> +#define SPINAND_READ_POLL_DELAY_US	5
> +#define SPINAND_RESET_INITIAL_DELAY_US	5
> +#define SPINAND_RESET_POLL_DELAY_US	5
> +#define SPINAND_WRITE_INITIAL_DELAY_US	75
> +#define SPINAND_WRITE_POLL_DELAY_US	15
> +#define SPINAND_ERASE_INITIAL_DELAY_US	250
> +#define SPINAND_ERASE_POLL_DELAY_US	50
> +
> +#define SPINAND_WAITRDY_TIMEOUT_MS	400
>  
>  /**
>   * struct spinand_id - SPI NAND id structure


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