[PATCH v1 1/2] mx6: ddr: Restore ralat/walat in write level calibration

[Fabio Estevam]

Hi Francesco,

On Wed, Apr 6, 2022 at 8:53 AM Francesco Dolcini
<francesco.dolcini at toradex.com> wrote:
>
> The current DDR write level calibration routine always overwrite
> the ralat/walat fields to their maximum value, just save
> the existing values at the beginning of the calibration routine
> and restore it at the end.
>
> In case the delay is estimated by the user to be more than one cycle the
> walat should be configured according to that, this is not
> automatically done.  From the i.MX6 RM:
>
>    The user should read the results of the associated delay-line at
>    MPWLDECTRL#[WL_DL_ABS_OFFSET#] and in case the user estimates that the
>    reasonable delay may be above 1 cycle then the user should indicate it at
>    MPWLDECTRL#[WL_CYC_DEL#]. Moreover the user should indicate it in
>    MDMISC[WALAT] field. For example, if the result of the write leveling calibration
>    is 100/256 parts of a cycle, but the user estimates that the delay is above 2 cycles
>    then MPWLDECTRL#[WL_CYC_DEL#] should be configured to 2, so the total
>    delay will be 2 and 100/256 parts of a cycle
>
> Probably it would just possible to not overwrite the mdmisc register in
> the first place, since this is not present in the write_level_calib() example
> in NXP AN4467 nor in the i.MX6 RM (44.11.6.1 Hardware Write Leveling
> Calibration).
>
> Fixes: d339f16911c7 ("arm: imx6: Add DDR3 calibration code for MX6 Q/D/DL")
> Signed-off-by: Francesco Dolcini <francesco.dolcini at toradex.com>
> Reviewed-by: Marek Vasut <marex at denx.de>

Reviewed-by: Fabio Estevam <festevam at denx.de>