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SubjectRe: [PATCH 3/7] mtd: spi-nor: add restriction for nmaps in smpt parser
On Thu, 8 Nov 2018 11:07:11 +0000
<Tudor.Ambarus@microchip.com> wrote:

> The map selector is limited to a maximum of 8 bits, allowing
> for a maximum of 256 possible map configurations. The total
> number of map configurations should be addressable by the
> total number of bits described by the detection commands.
>
> For example: if there are five to eight possible sector map
> configurations, at least three configuration detection commands
> will be needed to extract three bits of configuration selection
> information from the device in order to identify which configuration
> is currently in use.
>
> Suggested-by: Boris Brezillon <boris.brezillon@bootlin.com>

I don't remember suggesting this :-).

> Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
> ---
> drivers/mtd/spi-nor/spi-nor.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index 59dcedb08691..bd1866d714f2 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -2868,7 +2868,7 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
> const u32 *ret = NULL;
> u32 addr;
> int err;
> - u8 i;
> + u8 i, ncmds, nmaps;
> u8 addr_width, read_opcode, read_dummy;
> u8 read_data_mask, data_byte, map_id;
>
> @@ -2877,6 +2877,7 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
> read_opcode = nor->read_opcode;
>
> map_id = 0;
> + ncmds = 0;
> /* Determine if there are any optional Detection Command Descriptors */
> for (i = 0; i < smpt_len; i += 2) {
> if (smpt[i] & SMPT_DESC_TYPE_MAP)
> @@ -2896,6 +2897,7 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
> * Configuration that is currently in use.
> */
> map_id = map_id << 1 | !!(data_byte & read_data_mask);
> + ncmds++;
> }
>
> /*
> @@ -2905,7 +2907,16 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
> *
> * Find the matching configuration map.
> */
> - while (i < smpt_len) {
> + for (nmaps = 0; i < smpt_len; nmaps++) {
> + /*
> + * The map selector is limited to a maximum of 8 bits, allowing
> + * for a maximum of 256 possible map configurations. The total
> + * number of map configurations should be addressable by the
> + * total number of bits described by the detection commands.
> + */
> + if (ncmds && nmaps >= (1 << (ncmds + 1)))
> + break;
> +

Maybe I missed something but it sounds like this change is just
optimizing the SPMT parsing a bit, and to be honest, I'm not sure this
is really needed. Most of the time, smpt_len will be rather small, so
trying to bail out earlier is not bringing much perf improvements.

> if (SMPT_MAP_ID(smpt[i]) == map_id) {
> ret = smpt + i;
> break;

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