[PATCH] imx8m: fix reading of DDR4 MR registers

[sbabic@denx.de]

> I was trying to employ lpddr4_mr_read() to something similar to what
> the imx8mm-cl-iot-gate board is doing for auto-detecting the RAM
> type. However, the version in drivers/ddr/imx/imx8m/ddrphy_utils.c
> differs from the private one used by that board in how it extracts the
> byte value, and I was only getting zeroes. Adding a bit of debug
> printf'ing gives me
>  tmp = 0x00ffff00
>  tmp = 0x00070700
>  tmp = 0x00000000
>  tmp = 0x00101000
> and indeed I was expecting a (combined) value of 0xff070010 (0xff
> being Manufacturer ID for Micron). I can't find any documentation that
> says how the values are supposed to be read, but clearly the iot-gate
> definition is the right one, both for its use case as well as my
> imx8mp-based board.
> So lift the private definition of lpddr4_mr_read() from the
> imx8mm-cl-iot-gate board code to ddrphy_utils.c, and add a declaration
> in the ddr.h header where e.g. get_trained_CDD() is already declared.
> This has only been compile-tested for the imx8mm-cl-iot-gate
> board (since I don't have the hardware), but since I've merely moved
> its definition of lpddr4_mr_read(), I'd be surprised if it changed
> anything for that board.
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
> Tested-by: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org>
> Reviewed-by: Fabio Estevam <festevam@denx.de>
Applied to u-boot-imx, master, thanks !

Best regards,
Stefano Babic

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