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Message-ID: <e1f9652e-4dda-0420-69d3-6fef606bc5dd@gmail.com>
Date: Wed, 7 Dec 2016 17:20:59 +0100
From: Marek Vasut <marek.vasut@...il.com>
To: Cyrille Pitchen <cyrille.pitchen@...el.com>
Cc: computersforpeace@...il.com, boris.brezillon@...e-electrons.com,
richard@....at, linux-mtd@...ts.infradead.org,
linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
broonie@...nel.org
Subject: Re: [PATCH 2/2] mtd: spi-nor: add a stateless method to support
memory size above 128Mib
On 12/06/2016 05:52 PM, Cyrille Pitchen wrote:
> This patch provides an alternative mean to support memory above 16MiB
> (128Mib) by replacing 3byte address op codes by their associated 4byte
> address versions.
>
> Using the dedicated 4byte address op codes doesn't change the internal
> state of the SPI NOR memory as opposed to using other means such as
> updating a Base Address Register (BAR) and sending command to enter/leave
> the 4byte mode.
>
> Hence when a CPU reset occurs, early bootloaders don't need to be aware
> of BAR value or 4byte mode being enabled: they can still access the first
> 16MiB of the SPI NOR memory using the regular 3byte address op codes.
>
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@...el.com>
> Tested-by: Vignesh R <vigneshr@...com>
> ---
> drivers/mtd/spi-nor/spi-nor.c | 114 ++++++++++++++++++++++++++++++++++--------
> 1 file changed, 93 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index 8abe134e174a..606c030c566d 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -75,6 +75,10 @@ struct flash_info {
> * bit. Must be used with
> * SPI_NOR_HAS_LOCK.
> */
> +#define SPI_NOR_4B_OPCODES BIT(10) /*
> + * Use dedicated 4byte address op codes
> + * to support memory size above 128Mib.
> + */
> };
>
> #define JEDEC_MFR(info) ((info)->id[0])
> @@ -188,6 +192,91 @@ static inline struct spi_nor *mtd_to_spi_nor(struct mtd_info *mtd)
> return mtd->priv;
> }
>
> +
> +struct spi_nor_address_entry {
> + u8 src_opcode;
> + u8 dst_opcode;
> +};
> +
> +static u8 spi_nor_convert_opcode(u8 opcode,
> + const struct spi_nor_address_entry *entries,
> + size_t num_entries)
> +{
> + int min, max;
> +
> + /*
> + * This function implements a dichotomic search in the entries[]
> + * array indexed by src_opcode. Hence we assume that the entries[]
> + * array is sorted by src_opcode.
> + * The dichotomic search has a logarithmic complexity as opposed
> + * to a simple loop on all entires, which has a linear complexity:
> + * it means that when n is the number of entries in the input array,
> + * the dichotomic search performs O(log2(n)) comparisons whereas
> + * a simple loop performs O(n) comparisons.
> + */
> + min = 0;
> + max = num_entries - 1;
> + while (min <= max) {
> + int mid = (min + max) >> 1;
> + const struct spi_nor_address_entry *entry = &entries[mid];
> +
> + if (opcode == entry->src_opcode)
> + return entry->dst_opcode;
> +
> + if (opcode < entry->src_opcode)
> + max = mid - 1;
> + else
> + min = mid + 1;
> + }
You have like 16 entries in that table, just do a linear search, this is
only complex for no benefit.
> + /* No conversion found */
> + return opcode;
> +}
> +
> +static u8 spi_nor_3to4_opcode(u8 opcode)
> +{
> + /* MUST be sorted by 3byte opcode (cf spi_nor_convert_opcode). */
> +#define ENTRY_3TO4(_opcode) { _opcode, _opcode##_4B }
> + static const struct spi_nor_address_entry spi_nor_3to4_table[] = {
You can make this static const struct const for extra constness :-)
> + ENTRY_3TO4(SPINOR_OP_PP), /* 0x02 */
> + ENTRY_3TO4(SPINOR_OP_READ), /* 0x03 */
> + ENTRY_3TO4(SPINOR_OP_READ_FAST), /* 0x0b */
> + ENTRY_3TO4(SPINOR_OP_BE_4K), /* 0x20 */
> + ENTRY_3TO4(SPINOR_OP_PP_1_1_4), /* 0x32 */
> + ENTRY_3TO4(SPINOR_OP_PP_1_4_4), /* 0x38 */
> + ENTRY_3TO4(SPINOR_OP_READ_1_1_2), /* 0x3b */
> + ENTRY_3TO4(SPINOR_OP_BE_32K), /* 0x52 */
> + ENTRY_3TO4(SPINOR_OP_READ_1_1_4), /* 0x6b */
> + ENTRY_3TO4(SPINOR_OP_READ_1_2_2), /* 0xbb */
> + ENTRY_3TO4(SPINOR_OP_SE), /* 0xd8 */
> + ENTRY_3TO4(SPINOR_OP_READ_1_4_4), /* 0xeb */
I'd probably break this into three smaller tables, read/program/erase
and then call something like:
spi_nor_3to4_opcode(nor->read_opcode, read_opcode_table,
ARRAY_SIZE(read_opcode_table));
This would further reduce the table size (heck, it'd probably fit into a
cacheline), so linear search would be more than enough.
> + };
> +#undef ENTRY_3TO4
> +
> + return spi_nor_convert_opcode(opcode, spi_nor_3to4_table,
> + ARRAY_SIZE(spi_nor_3to4_table));
> +}
> +
> +static void spi_nor_set_4byte_opcodes(struct spi_nor *nor,
> + const struct flash_info *info)
> +{
> + /* Do some manufacturer fixups first */
> + switch (JEDEC_MFR(info)) {
> + case SNOR_MFR_SPANSION:
> + /* No small sector erase for 4-byte command set */
> + nor->erase_opcode = SPINOR_OP_SE;
> + nor->mtd.erasesize = info->sector_size;
> + break;
> +
> + default:
> + break;
> + }
> +
> + nor->read_opcode = spi_nor_3to4_opcode(nor->read_opcode);
> + nor->program_opcode = spi_nor_3to4_opcode(nor->program_opcode);
> + nor->erase_opcode = spi_nor_3to4_opcode(nor->erase_opcode);
> +}
> +
> /* Enable/disable 4-byte addressing mode. */
> static inline int set_4byte(struct spi_nor *nor, const struct flash_info *info,
> int enable)
> @@ -1486,27 +1575,10 @@ int spi_nor_scan(struct spi_nor *nor, const char *name, enum read_mode mode)
> else if (mtd->size > 0x1000000) {
> /* enable 4-byte addressing if the device exceeds 16MiB */
> nor->addr_width = 4;
> - if (JEDEC_MFR(info) == SNOR_MFR_SPANSION) {
> - /* Dedicated 4-byte command set */
> - switch (nor->flash_read) {
> - case SPI_NOR_QUAD:
> - nor->read_opcode = SPINOR_OP_READ_1_1_4_4B;
> - break;
> - case SPI_NOR_DUAL:
> - nor->read_opcode = SPINOR_OP_READ_1_1_2_4B;
> - break;
> - case SPI_NOR_FAST:
> - nor->read_opcode = SPINOR_OP_READ_FAST_4B;
> - break;
> - case SPI_NOR_NORMAL:
> - nor->read_opcode = SPINOR_OP_READ_4B;
> - break;
> - }
> - nor->program_opcode = SPINOR_OP_PP_4B;
> - /* No small sector erase for 4-byte command set */
> - nor->erase_opcode = SPINOR_OP_SE_4B;
> - mtd->erasesize = info->sector_size;
> - } else
> + if (JEDEC_MFR(info) == SNOR_MFR_SPANSION ||
> + info->flags & SPI_NOR_4B_OPCODES)
> + spi_nor_set_4byte_opcodes(nor, info);
> + else
> set_4byte(nor, info, 1);
> } else {
> nor->addr_width = 3;
>
--
Best regards,
Marek Vasut
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