[PATCH v3 4/4] mtd: rawnand: fsmc: Fix timing computation

[Miquel Raynal]

On Fri, 2021-11-19 at 15:03:16 UTC, Herve Codina wrote:
> Under certain circumstances, the timing settings calculated by
> the FSMC NAND controller driver were inaccurate.
> These settings led to incorrect data reads or fallback to
> timing mode 0 depending on the NAND chip used.
> 
> The timing computation did not take into account the following
> constraint given in SPEAr3xx reference manual:
>   twait >= tCEA - (tset * TCLK) + TOUTDEL + TINDEL
> 
> Enhance the timings calculation by taking into account this
> additional constraint.
> 
> This change has no impact on slow timing modes such as mode 0.
> Indeed, on mode 0, computed values are the same with and
> without the patch.
> 
> NANDs which previously stayed in mode 0 because of fallback to
> mode 0 can now work at higher speeds and NANDs which were not
> working at all because of the corrupted data work at high
> speeds without troubles.
> 
> Overall improvement on a Micron/MT29F1G08 (flash_speed tool):
>                         mode0       mode3
> eraseblock write speed  3220 KiB/s  4511 KiB/s
> eraseblock read speed   4491 KiB/s  7529 KiB/s
> 
> Fixes: d9fb079571833 ("mtd: nand: fsmc: add support for SDR timings")
> Signed-off-by: Herve Codina <herve.codina at bootlin.com>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/fixes, thanks.

Miquel