reset / watchdog on an imx7d soc

[Giorgio Dal Molin]

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.

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.

giorgio

> 
> > 
> > giorgio
> > 
> > 
> >>
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