imx8m: fix reading of DDR4 MR registers

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>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/arm/include/asm/arch-imx8m/ddr.h b/arch/arm/include/asm/arch-imx8m/ddr.h
index 0f1e832c03..2ce8a8f2d4 100644
--- a/arch/arm/include/asm/arch-imx8m/ddr.h
+++ b/arch/arm/include/asm/arch-imx8m/ddr.h
@@ -723,6 +723,7 @@ void ddrphy_init_read_msg_block(enum fw_type type);
 
 void update_umctl2_rank_space_setting(unsigned int pstat_num);
 void get_trained_CDD(unsigned int fsp);
+unsigned int lpddr4_mr_read(unsigned int mr_rank, unsigned int mr_addr);
 
 static inline void reg32_write(unsigned long addr, u32 val)
 {