reset / watchdog on an imx7d soc

[Ahmad Fatoum]

Hello Giorgio,

On 6/29/20 5:30 PM, Giorgio Dal Molin wrote:
> Hi,
> 
>> On June 29, 2020 at 3:30 PM Ahmad Fatoum <a.fatoum at pengutronix.de> wrote:
>>
>>
>> Hello,
>>
>> On 6/29/20 12:53 PM, Giorgio Dal Molin wrote:
>>> Hi,
>>>
>>>> On June 29, 2020 at 10:44 AM Ahmad Fatoum <a.fatoum at pengutronix.de> wrote:
>>>>
>>>>
>>>> Hello Giorgio,
>>>>
>>>> On 6/23/20 5:11 PM, Giorgio Dal Molin wrote:
>>>>> Hi Fabio,
>>>>>
>>>>> thank you for your quick reply.
>>>>>
>>>>> I've already found the errata you linked in your mail but I had no success
>>>>> applying the suggestion there; maybe I'm doing it wrong.
>>>>> Let's take the Option 3 there:
>>>>
>>>> Does reset within Linux (with say the imx_v6_v7_defconfg) work?
>>>
>>> No. I see the same behavior also with the kernel: after a 'shutdown -r'
>>> the system 'goes down' but doesn't reboot, it just hang:
>>>
>>> ~ # shutdown -r
>>> system is going down for reboot NOW
>>> ...
>>> [   46.248222] 000: ci_hdrc ci_hdrc.0: remove, state 1
>>> [   46.248253] 000: usb usb1: USB disconnect, device number 1
>>> [   46.248263] 000: usb 1-1: USB disconnect, device number 2
>>>
>>>
>>> The same happens if I kill the 'watchdog' process: after ~2 seconds
>>> the system just hangs.
>>>
>>> I'm sure there must be a solution because the original u-boot bootloader
>>> for the cpu module I'm using reboots the system as expected, through the wdog1;
>>> unfortunately it's not so trivial to find what makes the difference.
>>
>> Linux probably attempts reset via PSCI. Check for psci_system_reset
>> in your vendor's U-Boot and transplant it into barebox.
> 
> U-Boot has actually a psci_system_reset(), it also rely on wdog1:
> 
> __secure void psci_system_reset(void)
> {
> 	struct wdog_regs *wdog = (struct wdog_regs *)WDOG1_BASE_ADDR;
> 
> 	/* make sure WDOG1 clock is enabled */
> 	writel(0x1 << 28, CCM_BASE_ADDR + CCM_ROOT_WDOG);
> 	writel(0x3, CCM_BASE_ADDR + CCM_CCGR_WDOG1);
> 	writew(WCR_WDE, &wdog->wcr);
> 
> 	while (1)
> 		wfi();
> }
> 
> It is also compiled in the uboot image, because if I add a syntax error in
> its body the compiler tells me; anyway I think it's not called when I issue
> the 'reset' command at the prompt because the 'reset' works properly even if
> I comment out the whole body of the function or if I add an endless loop like
> while(1); to it.

Yes. It should be called by the kernel when CONFIG_ARM_PSCI_FW=y
and the device tree has the correct node. 
> Anyway I ported it to barebox, defining a void psci_system_reset(void) in
> arch/arm/mach-imx/imx7.c:
> 
> ...
> #define CCM_BASE_ADDR   0x30380000
> #define CCM_ROOT_WDOG   0xbb80
> #define CCM_CCGR_WDOG1  0x49c8
> #define WCR_WDE	        0x04
> #define WDOG1_WCR       0x30280000
> #define wfi() __asm__ __volatile__ ("wfi" : : : "memory")
> 
> static void imx7_system_reset(void)
> {
> 	printf("%s: called now.\n",__func__);
> 
> 	// make sure WDOG1 clock is enabled
> 	writel(0x1 << 28, CCM_BASE_ADDR + CCM_ROOT_WDOG);
> 	writel(0x3, CCM_BASE_ADDR + CCM_CCGR_WDOG1);
> 	writew(WCR_WDE, WDOG1_WCR);
> 
> 	while (1)
> 		wfi();
> };
> 
> static struct psci_ops imx7_psci_ops = {
> 	.cpu_on = imx7_cpu_on,
> 	.cpu_off = imx7_cpu_off,
> 	.system_reset = imx7_system_reset,
> };
> 
> and the following case to smc.c:
> 
> static int do_smc(int argc, char *argv[])
> {
> ...
> 		case 'r':
> 			printf("issue psci reset...\n");
> 			arm_smccc_smc(ARM_PSCI_0_2_FN_SYSTEM_RESET,
> 				      0, 0, 0, 0, 0, 0, 0, &res);
> 			printf("reset issued...\n");
> 			break;
> ...
> 
> to be able to call it.
> Now, using the modified 'smc' command I can see my printf's:
> 
> samx7: / smc -n
> samx7: / smc -r
> issue psci reset...
> psci_system_reset called.
> imx7_system_reset: called now.
> 
> but the soc still just hangs.

What does U-Boot's reset commando do on an i.MX7?

> 
> giorgio
> 
>>
>>>
>>> giorgio
>>>
>>>
>>>>
>>>> -- 
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>>>
>>
>> -- 
>> Pengutronix e.K.                           |                             |
>> Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
>> 31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
>> Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |
>>
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> 

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Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |