iMX8MN: U-Boot does not work with 64MiB SPI NOR flash

[swendt38]

Hi, we are using i.MX8M Nano with U-Boot 2020.04 and our design is custom but based on DDR4 Audio board 2.0.

Our QSPI NOR flash is a n25q512a from Micron and is supported by U-Boot in general.

So far everything looks ok except that we can not properly access addresses beyond the lower 32 Megabytes (so >0x02000000).

When we boot from SPI flash and try to access the higher addresses, we run into a reset.

When we boot from USB (using uuu), we do not get a reset but the content of those upper 32 Megabytes is rubbish.

Using Linux we can access the entire flash range without restrictions.

It seems there is a limitation (e.g. memory mapping) for iMX8MN and U-Boot accessing addresses >32MiB on SPI NOR flashes.

Does anybody know a reason ?

[igorpadykov]

Hi Sebastian

for that issue one can try to enable 4-byte address mode (3-byte is used by default)

which can be enabled through the nonvolatile configuration register. Details can be found

in n25q512a datasheet.

Best regards
igor

[swendt38]

Hi Igor,

thanks for your reply.

I assume we are already using 4-Byte addressing because we can access addresses >16MiB (which exceeds 3-Byte address range).

I suspect the issue is more related to mapping the QSPI flash addresses to the memory range of the iMX8MN.

Regards,

Sebastian

[swendt38 · Accepted solution]

Hi,

I found the issue - the flash size is not taken from the SPI NOR ID table but has to be defined separately inside imx8mn_ab2.h which is of course not very nice but looks like solves my issue.

Regards,

Sebastian

[swendt38]

Same issue is valid for eMMC - but here offset is 32KiB.