[U-Boot] [PATCH 1/1] ARM: mxs: Get boot mode from OCRAM

[Robert Deliën]

> The GLOBAL_BOOT_MODE_ADDR for i.MX28 is taken from an U-Boot patch for the
> MX28EVK:
> http://repository.timesys.com/buildsources/u/u-boot/u-boot-2009.08/u-boot-2009.08-mx28-201012211513.patch

It could be 0x0001a7f0 too:
/* The global boot mode will be detected by ROM code and
 * a boot mode value will be stored at fixed address:
 * TO1.0 addr 0x0001a7f0
 * TO1.2 addr 0x00019BF0
 */
#ifndef MX28_EVK_TO1_0
 #define GLOBAL_BOOT_MODE_ADDR 0x00019BF0
#else
 #define GLOBAL_BOOT_MODE_ADDR 0x0001a7f0
#endif
Probably depending on the silicon spin, so perhaps we want to make a CONFIG_ for older silicon.

And the numbers read at this address don't match the numbers read from the boot mode GPIO pin. Only the lowest 4 bits represent the actual boot device and below the definitions:
#define BOOT_MODE_USB0                  0x0
#define BOOT_MODE_I2C0                  0x1
#define BOOT_MODE_SPI2                  0x2
#define BOOT_MODE_SPI3                  0x3
#define BOOT_MODE_GPMI                  0x4
#define BOOT_MODE_rsvd1                 0x5
#define BOOT_MODE_JTAG                  0x6
#define BOOT_MODE_rsvd3                 0x7
#define BOOT_MODE_SPI3_EE               0x8
#define BOOT_MODE_SSP0                  0x9
#define BOOT_MODE_SSP1                  0xa
#define BOOT_MODE_rsvd4                 0xb
#define BOOT_MODE_rsvd5                 0xc
#define BOOT_MODE_rsvd6                 0xd
#define BOOT_MODE_rsvd7                 0xe
#define BOOT_MODE_TEST                  0xf
Higher bits have other purposes. On my board, for example, a value of 0x14 is reported when booting from NAND flash.

Having said all of this, I think your way is definitely the way to go.