Re: imx7d dual core boot

[Giorgio <giorgio.nicole@arcor.de>]

Hi Ahmad,

I've also tried the arm_v7_defconfig + my board specific code but it does not
solve the problem.

The setup I'm using to build barebox just include support for my board; in my
board code, under arch/arm/boards/kontron-samx7, I've nothing special, just
a custom init script in the environment.

To trigger the code that makes barebox hang I use now the command
'smc -n': it calls armv7_secure_monitor_install() and then __mmu_cache_on()
that finally jumps to 'v7_mmu_cache_on'.

Searching in the Armv7-A ref. man. here:

https://static.docs.arm.com/ddi0406/cd/DDI0406C_d_armv7ar_arm.pdf

at B4.1.43 (page B4 - 1554) I found that the reset value of this cp15 reg.
is UNKNOWN and I can also verify this. Moreover the reg. must also be
banked: there is a copy in secure mode and one in nonsecure mode.
My test consists in reading the register just before and just after
the call to arm_smccc_smc(0, 0, 0, 0, 0, 0, 0, 0, &res):

static u32 read_dacr(void)
{
	unsigned int reg;

	asm volatile ("mrc p15, 0, %0, c3, c0, 0\n" : "=r"(reg));
	return reg;
}

...

int __armv7_secure_monitor_install(void)
{
...
	printf("%s: 1) dacr: 0x%08x\n",__func__,read_dacr());

	/* Initialize the secure monitor */
	arm_smccc_smc(0, 0, 0, 0, 0, 0, 0, 0, &res);

	/* We're in nonsecure mode now */

	printf("%s: 2) dacr: 0x%08x\n",__func__,read_dacr());
	
	return 0;
}

and here is what I get:

samx7: / smc -n
__armv7_secure_monitor_install: 1) dacr: 0x00000001
__armv7_secure_monitor_install: 2) dacr: 0xdbf7afaa

If I write a 0x1 or a 0x3 to DACR just before enabling the MMU in
nonsecure mode then barebox does not hang.

giorgio

On 2020-04-06 08:16, Ahmad Fatoum wrote:
> Hello Giorgio,
> 
> On 4/3/20 3:47 PM, Giorgio wrote:
>> Hi Ahmad,
>>
>> thank you for the detailed explanations, I'll have a look
>> at the armv7 ref. manual for more background.
>>
>> I wanted just to note, the problem is specifically linked
>> to enabling the MMU:
>>
>> in arch/arm/cpu/cache-armv7.S:
>>
>>
>> 		orrne	r0, r0, #1		@ MMU enabled
>> ...
>> 		mcr	p15, 0, r0, c1, c0, 0	@ load control register
>>
>> without the 'orrne ...' the imx7 does not hang.
> 
> I can't reproduce this exact problem. My setup:
> 
> - i.MX7D sabresd board,
> - imx_v7_defconfig
> - check out of upstream/next, commit 5931fe40 ("Merge branch 'for-next/zii' into next")
> - revert of commit 8b2104d ("driver: Call of_clk_set_defaults for each probed device")
> - nv bootm.secure_state=nonsecure
> 
> With this, I didn't observe any barebox hangs[1] while preparing a Linux net boot.
> What's your setup?
> 
> [1]: Linux still hangs due to what I assume to be a psci issue, kernel log says
>      "unsupported enable-method property: psci" before getting stuck durcing SDHCI probe
> 

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