Linux/AM5718: Memory booting device descriptor

So for your first question, when the boot ROM transfers control to SPL, the address of the booting parameters structure is in r0. Early in lowlevel_init.S it is save into SRAM from a call to save_boot_params. The code is below

ENTRY(save_boot_params)
ldr r1, =OMAP_SRAM_SCRATCH_BOOT_PARAMS
str r0, [r1]
b save_boot_params_ret
ENDPROC(save_boot_params)

In save_omap_boot_params, the boot device is determined by this code

omap_boot_params = (struct omap_boot_parameters *)boot_params;
boot_device = omap_boot_params->boot_device;

The omap_boot_parameters structure is in arch/arm/include/asm/arch-omap5/omap.h and maps to the structure in the TRM

struct omap_boot_parameters {
unsigned int boot_message;
unsigned int boot_device_descriptor;
unsigned char boot_device;
unsigned char reset_reason;
unsigned char ch_flags;
};

So boot_device is the boot device the ROM set in the structure.

For your second question, the control_status is not the one in prcm-regs.c. It is in the structure sys_ctrl_regs in arch/arm/include/asm/omap_common.h

struct omap_sys_ctrl_regs {
u32 control_status;
u32 control_core_mac_id_0_lo;
u32 control_core_mac_id_0_hi;

Steve K.

First let me thank you for clearing up my confusion about my second question.  I now see how that works.

As to my first question, I had been able to follow the description in the TRM and the code down to the point where struct omap_boot_parameters is populated.  At that point, I'm trying to understand the computation of boot_mode.  For my hardware/configuration, the code flow eventually gets to save_omap_boot_params() in arch/arm/mach-omap2/boot-common.c.  There are several points in the flow that boot_mode can potentially be determined but for my world, none of those points are hit until the flow gets to around line 132 (at least in the version of boot-common.c that came with the SDK we started with).  Ignoring all the error checks, here's the essential computation:

	boot_params = omap_boot_params->boot_device_descriptor;
	boot_params = *((u32 *)(boot_params + DEVICE_DATA_OFFSET));
	boot_mode = *((u32 *)(boot_params + BOOT_MODE_OFFSET));

So it's what boot_device_descriptor looks like that is of interest.  The TRM documents all the fields that comprise struct omap_boot_parameters except, as far as I can tell, boot_device_descriptor. The TRM has some references to "device_descriptor" but in all cases, it's in the context of USB and that's clearly not my situation nor does the USB device_descriptor have a layout compatible with the above code.  The only documentation in the code concerning those two offsets (found in arch/arm/include/asm/omap_common.h) is that they are "Boot parameters".

EDIT: looks like something happened when I was pasting the code . Those "strong" tags in the first line aren't there. The line is just:

boot_params = omap_boot_params->boot_device_descriptor;

Which SDK are you using?

Steve K.

The guy that knows the SDK version isn't around at the moment but I had earlier managed to figure out where we are with respect to TI's U-Boot tree at git://git.ti.com/ti-u-boot/ti-u-boot.git. We are at tag ti2017.04-rc1.

I have asked the TRM owner if there is a description somewhere.

Steve K.