reset / watchdog on an imx7d soc

[Ahmad Fatoum]

On 7/1/20 11:52 AM, Giorgio Dal Molin wrote:
> Hi,
> 
>> On June 29, 2020 at 6:39 PM Fabio Estevam <festevam at gmail.com> wrote:
>>
>>
>> Hi Giorgio,
>>
>> On Mon, Jun 29, 2020 at 1:33 PM Giorgio Dal Molin
>> <giorgio.nicole at arcor.de> wrote:
>>
>>> U-Boot configures the ddr3 with c code in its board code 'lowlevel.c'.
>>> Looking at the code I noticed this special treatment:
>>>
>>> static void spl_dram_init(void)
>>> {
>>> ...
>>>         /*
>>>          * Make sure that both aresetn/core_ddrc_rstn and preset/PHY reset
>>>          * bits are set after WDOG reset event. DDRC_PRST can only be
>>>          * released when DDRC clock inputs are stable for at least 30 cycles.
>>>          */
>>>         writel(SRC_DDRC_RCR_DDRC_CORE_RST_MASK | SRC_DDRC_RCR_DDRC_PRST_MASK, &src_regs->ddrc_rcr);
>>>         udelay(500);
>>> ...
>>>
>>> This writel() set both reset bits, the DDRC_CORE (0x2) and the DDRC_PRST (0x1) of the SRC
>>> register 0x30391000.
>>> Unfortunately, if I try also to set both bits in my DCD table then barebox doesn't boot anymore;
>>> I also tried to port the uboot spl_dram_init(void) to my barebox lowlevel.c and I could eventually
>>> boot barebox with an empty DCD but still adding the second bit (SRC_DDRC_RCR_DDRC_PRST_MASK)
>>> hangs the soc.
>>
>> Does it help if you try to apply this U-Boot commit to Barebox?
>> https://gitlab.denx.de/u-boot/u-boot/-/commit/0e06d63d195670f5181958f43216d7106c05357f
> 
> I've made some more tests with the imx7d and found that the following DCD sequence:
> 
> wm 32 0x30391000		0x00000003  // <== added this write
> wm 32 0x30391000		0x00000002
> ...
> 
> have an (unreliable) effect: I can now some time reboot barebox with a 'reset'
> command and after the reboot I can see the correct reset reason on the serial console:
> 
> barebox 2020.06.0-00327-g712fde835-dirty #2 Wed Jul 1 10:21:11 CEST 2020
> 
> Board: Kontron SMARC-sAMX7
> detected i.MX7d revision 1.3
> i.MX reset reason POR (SRSR: 0x00000001)
> ...
> 
> samx7: /
> samx7: / reset 
> 
> barebox 2020.06.0-00327-g712fde835-dirty #2 Wed Jul 1 10:21:11 CEST 2020
> 
> Board: Kontron SMARC-sAMX7
> detected i.MX7d revision 1.3
> i.MX reset reason WDG (SRSR: 0x00000010)
> mdio_bus: miibus0: probed
> ...
> 
> samx7: /
> 
> 
> This is the first time I see a reset working on my imx7 module with barebox; the
> problem is now that the reboot process is not reliable: it works a couple of times
> (not deterministic) and then it hangs the soc forcing me to push the reset button.
> 
> As a possible fix I tried adding some 'nop' in the DCD around the two wm 32 to simulate
> a delay but it makes no difference.

IIRC, you can poll an address for a set bit in the DCD table for N times. If you poll
something that doesn't change, you can adjust N to simulate a delay..

> 
> giorgio
> 
>>
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> 

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