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SubjectRe: [RFC PATCH] mtd: spi-nor: add support to non-uniform SPI NOR flash memories
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On 05/18/2018 11:32 AM, Tudor Ambarus wrote:
> From: Cyrille Pitchen <cyrille.pitchen@microchip.com>
>
> This patch is a first step in introducing the support of SPI memories
> with non-uniform erase sizes like Spansion s25fs512s.
>
> It introduces the memory erase map which splits the memory array into one
> or many erase regions. Each erase region supports up to 4 erase commands,
> as defined by the JEDEC JESD216B (SFDP) specification.
> In turn, an erase command is defined by an op code and a sector size.
>
> To be backward compatible, the erase map of uniform SPI NOR flash memories
> is initialized so it contains only one erase region and this erase region
> supports only one erase command. Hence a single size is used to erase any
> sector/block of the memory.
>
> Besides, since the algorithm used to erase sectors on non-uniform SPI NOR
> flash memories is quite expensive, when possible, the erase map is tuned
> to come back to the uniform case.
>
> This is a transitional patch: non-uniform erase maps will be used later
> when initialized based on the SFDP data.

What about non-SFDP non-linear flashes ?

> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@microchip.com>
>
> [tudor.ambarus@microchip.com:
> - add improvements on how the erase map is handled. The map is an array
> describing the boundaries of the erase regions. LSB bits of the region's
> offset are used to describe the supported erase types, to indicate if
> that specific region is the last region in the map and to mark if the
> region is overlaid or not. When one sends an addr and len to erase a
> chunk of memory, we identify in which region the address fits, we start
> erasing with the best fitted erase commands and when the region ends,
> continue to erase from the next region. The erase is optimal: identify
> the start offset (once), then erase with the best erase command,
> move forward and repeat.

Is that like an R-tree ?

> - order erase types by size, with the biggest erase type at BIT(0). With
> this, we can iterate from the biggest supported erase type to the smallest,
> and when find one that meets all the required conditions, break the loop.
> This saves time in determining the best erase cmd.
>
> - minimize the amount of erase() calls by using the best sequence of erase
> type commands depending on alignment.

Nice, this was long overdue

> - replace spi_nor_find_uniform_erase() with spi_nor_select_uniform_erase().
> Even for the SPI NOR memories with non-uniform erase types, we can determine
> at init if there are erase types that can erase the entire memory. Fill at
> init the uniform_erase_type bitmask, to encode the erase type commands that
> can erase the entire memory.
>
> - clarify support for overlaid regions. Considering one of the erase maps
> of the S25FS512S memory:
> Bottom: 8x 4KB sectors at bottom (only 4KB erase supported),
> 1x overlaid 224KB sector at bottom (only 256KB erase supported),
> 255x 256KB sectors (only 256KB erase supported)
> S25FS512S states that 'if a sector erase command is applied to a 256KB range
> that is overlaid by 4KB secors, the overlaid 4kB sectors are not affected by
> the erase'. When at init, the overlaid region size should be set to
> region->size = erase_size - count; in order to not miss chunks of data
> when traversing the regions.
>
> - backward compatibility test done on MX25L25673G.
>
> The 'erase with the best command, move forward and repeat' approach was
> suggested by Cristian Birsan in a brainstorm session, so:
> ]
> Suggested-by: Cristian Birsan <cristian.birsan@microchip.com>
> Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
> ---
> drivers/mtd/spi-nor/spi-nor.c | 281 +++++++++++++++++++++++++++++++++++++++---
> include/linux/mtd/spi-nor.h | 89 +++++++++++++
> 2 files changed, 356 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index 494b7a2..bb70664 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -260,6 +260,17 @@ static void spi_nor_set_4byte_opcodes(struct spi_nor *nor,
> nor->read_opcode = spi_nor_convert_3to4_read(nor->read_opcode);
> nor->program_opcode = spi_nor_convert_3to4_program(nor->program_opcode);
> nor->erase_opcode = spi_nor_convert_3to4_erase(nor->erase_opcode);
> +
> + if (!spi_nor_has_uniform_erase(nor)) {
> + struct spi_nor_erase_map *map = &nor->erase_map;
> + struct spi_nor_erase_command *cmd;
> + int i;
> +
> + for (i = 0; i < SNOR_CMD_ERASE_MAX; i++) {
> + cmd = &map->commands[i];
> + cmd->opcode = spi_nor_convert_3to4_erase(cmd->opcode);
> + }
> + }
> }
>
> /* Enable/disable 4-byte addressing mode. */
> @@ -497,6 +508,131 @@ static int spi_nor_erase_sector(struct spi_nor *nor, u32 addr)
> return nor->write_reg(nor, nor->erase_opcode, buf, nor->addr_width);
> }
>
> +/* JEDEC JESD216B Standard imposes erase sizes to be power of 2. */
> +static inline u64
> +spi_nor_div_by_erase_size(const struct spi_nor_erase_command *cmd,
> + u64 dividend, u32 *remainder)
> +{
> + *remainder = (u32)dividend & cmd->size_mask;
> + return dividend >> cmd->size_shift;
> +}
> +
> +static const struct spi_nor_erase_command *
> +spi_nor_find_best_erase_cmd(const struct spi_nor_erase_map *map,
> + const struct spi_nor_erase_region *region, u64 addr,
> + u32 len)
> +{
> + const struct spi_nor_erase_command *cmd;
> + u32 rem;
> + int i;
> + u8 cmd_mask = region->offset & SNOR_CMD_ERASE_MASK;
> +
> + /*
> + * Commands are ordered by size, with the biggest erase type at
> + * index 0.
> + */
> + for (i = 0; i < SNOR_CMD_ERASE_MAX; i++) {
> + /* Does the erase region support the tested erase command? */
> + if (!(cmd_mask & BIT(i)))
> + continue;
> +
> + cmd = &map->commands[i];
> +
> + /* Don't erase more than what the user has asked for. */
> + if (cmd->size > len)
> + continue;

Are you sure checking for the full erase block length first and then
checking if you can sub-erase the block is OK ?

> + if (!(region->offset & SNOR_OVERLAID_REGION)) {
> + /* 'addr' must be aligned to the erase size. */
> + spi_nor_div_by_erase_size(cmd, addr, &rem);
> + continue;
> + } else {
> + /*
> + * 'cmd' will erase the remaining of the overlaid
> + * region.
> + */
> + return cmd;
> + }
> + }
> +
> + return NULL;
> +}
> +
> +static const struct spi_nor_erase_region *
> +spi_nor_region_next(const struct spi_nor_erase_region *region)
> +{
> + if (spi_nor_region_is_last(region))
> + return NULL;
> + region++;
> + return region;
> +}
> +
> +static const struct spi_nor_erase_region *
> +spi_nor_find_erase_region(const struct spi_nor_erase_map *map, u64 addr,
> + u32 len)
> +{
> + const struct spi_nor_erase_region *region = map->regions;
> + u64 region_start = region->offset & ~SNOR_ERASE_FLAGS_MASK;
> + u64 region_end = region_start + region->size;
> +
> + if (!len)
> + return ERR_PTR(-EINVAL);
> +
> + while (addr < region_start || addr > region_end) {
> + region = spi_nor_region_next(region);
> + if (!region)
> + return ERR_PTR(-EINVAL);
> +
> + region_start = region->offset & ~SNOR_ERASE_FLAGS_MASK;
> + region_end = region_start + region->size;
> + }
> +
> + return region;
> +}
> +
> +static int spi_nor_erase_multi_sectors(struct spi_nor *nor, u64 addr, u32 len)
> +{
> + const struct spi_nor_erase_map *map = &nor->erase_map;
> + const struct spi_nor_erase_command *cmd;
> + const struct spi_nor_erase_region *region;
> + u64 region_end;
> + int ret;
> +
> + region = spi_nor_find_erase_region(map, addr, len);
> + if (IS_ERR(region))
> + return PTR_ERR(region);
> +
> + region_end = spi_nor_region_end(region);
> +
> + while (len) {
> + cmd = spi_nor_find_best_erase_cmd(map, region, addr, len);
> + if (!cmd)
> + return -EINVAL;

What would happen if you realize mid-way that you cannot erase some
sector , do you end up with partial erase ?
[...]

--
Best regards,
Marek Vasut

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