Re: [PATCH v4 1/7] mtd: spi-nor: sfdp: get octal mode maximum speed from BFPT

[<Tudor.Ambarus@microchip.com>]

Hi, Mason, YC Lin,

On 5/29/20 10:36 AM, Mason Yang wrote:
> Get maximum operation speed of device in octal mode from
> BFPT 20th DWORD.
> 

I would like to understand how would we use the max speed value
at the SPI NOR level. The maximum operation speed is typically used
to determine the number of dummy cycles, which is described in xSPI
Spec for speeds of 200 MHz or less. Even if BFPT[dword20] describes
supported speeds up to 400 MHz, it doesn't indicate the number of
required dummy cycles. What number of dummy cycles would we use for
speeds higher than 200 MHz?

We may be tempted however to pass the max_speed_hz to the SPIMEM layer,
so that the controller can sync with the memory to choose the best
available speed.

Cheers,
ta

> Signed-off-by: Mason Yang <masonccyang@mxic.com.tw>
> ---
>  drivers/mtd/spi-nor/core.h |  2 ++
>  drivers/mtd/spi-nor/sfdp.c | 36 ++++++++++++++++++++++++++++++++++++
>  drivers/mtd/spi-nor/sfdp.h |  4 ++++
>  3 files changed, 42 insertions(+)
> 
> diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
> index 6f2f6b2..7a36b22 100644
> --- a/drivers/mtd/spi-nor/core.h
> +++ b/drivers/mtd/spi-nor/core.h
> @@ -190,6 +190,7 @@ struct spi_nor_locking_ops {
>   *
>   * @size:		the flash memory density in bytes.
>   * @page_size:		the page size of the SPI NOR flash memory.
> + * @octal_max_speed:	maximum operation speed of device in octal mode.
>   * @hwcaps:		describes the read and page program hardware
>   *			capabilities.
>   * @reads:		read capabilities ordered by priority: the higher index
> @@ -212,6 +213,7 @@ struct spi_nor_locking_ops {
>  struct spi_nor_flash_parameter {
>  	u64				size;
>  	u32				page_size;
> +	u16				octal_max_speed;
>  
>  	struct spi_nor_hwcaps		hwcaps;
>  	struct spi_nor_read_command	reads[SNOR_CMD_READ_MAX];
> diff --git a/drivers/mtd/spi-nor/sfdp.c b/drivers/mtd/spi-nor/sfdp.c
> index f6038d3..4d13f66 100644
> --- a/drivers/mtd/spi-nor/sfdp.c
> +++ b/drivers/mtd/spi-nor/sfdp.c
> @@ -4,6 +4,7 @@
>   * Copyright (C) 2014, Freescale Semiconductor, Inc.
>   */
>  
> +#include <linux/bitfield.h>
>  #include <linux/slab.h>
>  #include <linux/sort.h>
>  #include <linux/mtd/spi-nor.h>
> @@ -26,6 +27,12 @@
>  #define SFDP_JESD216A_MINOR	5
>  #define SFDP_JESD216B_MINOR	6
>  
> +/* Basic Flash Parameter Table 20th DWORD, Max operation speed of device */
> +struct octal_max_speed {
> +	u8 idx; /* Bits value */
> +	u16 hz; /* MHz */
> +};
> +
>  struct sfdp_header {
>  	u32		signature; /* Ox50444653U <=> "SFDP" */
>  	u8		minor;
> @@ -440,6 +447,22 @@ static int spi_nor_parse_bfpt(struct spi_nor *nor,
>  	u32 addr;
>  	u16 half;
>  	u8 erase_mask;
> +	static const struct octal_max_speed max_hz[] = {
> +		/* Bits value, MHz */
> +		{ 0x0c, 400 },
> +		{ 0x0b, 333 },
> +		{ 0x0a, 266 },
> +		{ 0x09, 250 },
> +		{ 0x08, 200 },
> +		{ 0x07, 166 },
> +		{ 0x06, 133 },
> +		{ 0x05, 100 },
> +		{ 0x04,  80 },
> +		{ 0x03,  66 },
> +		{ 0x02,  50 },
> +		{ 0x01,  33 },
> +	};
> +	u8 idx;
>  
>  	/* JESD216 Basic Flash Parameter Table length is at least 9 DWORDs. */
>  	if (bfpt_header->length < BFPT_DWORD_MAX_JESD216)
> @@ -604,6 +627,19 @@ static int spi_nor_parse_bfpt(struct spi_nor *nor,
>  		return -EINVAL;
>  	}
>  
> +	/* Octal mode max speed */
> +	idx = max(FIELD_GET(BFPT_DWORD20_OCTAL_DTR_MAX_SPEED,
> +			    bfpt.dwords[BFPT_DWORD(20)]),
> +		  FIELD_GET(BFPT_DWORD20_OCTAL_STR_MAX_SPEED,
> +			    bfpt.dwords[BFPT_DWORD(20)]));
> +
> +	for (i = 0; i < ARRAY_SIZE(max_hz); i++) {
> +		if (max_hz[i].idx == idx) {
> +			params->octal_max_speed = max_hz[i].hz;
> +			break;
> +		}
> +	}
> +
>  	return spi_nor_post_bfpt_fixups(nor, bfpt_header, &bfpt, params);
>  }
>  
> diff --git a/drivers/mtd/spi-nor/sfdp.h b/drivers/mtd/spi-nor/sfdp.h
> index e0a8ded..8ae6d9a 100644
> --- a/drivers/mtd/spi-nor/sfdp.h
> +++ b/drivers/mtd/spi-nor/sfdp.h
> @@ -83,6 +83,10 @@ struct sfdp_bfpt {
>  #define BFPT_DWORD15_QER_SR2_BIT1_NO_RD		(0x4UL << 20)
>  #define BFPT_DWORD15_QER_SR2_BIT1		(0x5UL << 20) /* Spansion */
>  
> +#define BFPT_DWORD20_OCTAL_MAX_SPEED_MASK       GENMASK(31, 16)
> +#define BFPT_DWORD20_OCTAL_DTR_MAX_SPEED        GENMASK(31, 28)
> +#define BFPT_DWORD20_OCTAL_STR_MAX_SPEED        GENMASK(19, 16)
> +
>  struct sfdp_parameter_header {
>  	u8		id_lsb;
>  	u8		minor;
>