[U-Boot] ti: ARM: svc: Question about switching to am57xx HYP mode.

[Lukasz Majewski <lukma@denx.de>]

Dear All,

I do have a question regarding switching from SVC to HYP mode on AM57xx
SoC.

Just after going out of reset (room bootloader):
------------------------------------------------

Breakpoint 1, _start () at arch/arm/lib/vectors.S:54
54              b       reset
(gdb) mo info
    Core number       : 0
    Core state        : debug mode (ARM)
    Debug entry cause : Breakpoint
    Current PC        : 0x40300000
    Current CPSR      : 0x400000d3 (Supervisor)
    Current SPSR      : 0x00000000
(gdb) 

Here the A bit in CPSR is cleared - the "Imprecise Data Abort mask" is
disabled.

Then we enter the HYP mode (due to LPAE u-boot support):
Breakpoint 39, switch_to_hypervisor () at
arch/arm/cpu/armv7/omap-common/lowlevel_init.S:35

After end of this ASM procedure we got following CPSR for HYP mode:

Breakpoint 41, switch_to_hypervisor_ret () at
arch/arm/cpu/armv7/start.S:57 57              and     r1, r0,
#0x1f           @ mask mode bits (gdb) mo info
    Core number       : 0
    Core state        : debug mode (ARM)
    Debug entry cause : Breakpoint
    Current PC        : 0x4030005c
    Current CPSR      : 0x000001da (Hyp)
    Current SPSR      : 0x00000010
(gdb) 

And here the A bit "Imprecise Abort Bit" [8] is masked.

Why such operation is performed in the SMC call (which switches to HYP)?

I could try to disable it by hand (cpsie A), but I'm not sure if this
has no "side effects".




Best regards,

Lukasz Majewski

--

DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de