iMX7D resets when MIPI DSI initialises

[chris_saunders]

I have a custom board with an iMX7D which uses MIPI DSI to interface with a LCD display. The MIPI DSI power configuration is taken from the SABRESD dev board which was used to do initial dev work on the display drivers which are working. My device tree is a modified version of the SABRESD with all unused devices removed.

When Linux progresses through startup, I get the console output "mxsfb 30730000.lcdif: registered mxc display driver mipi_dsi_samsung" and then the board resets and U-Boot is restarted.

I have managed to debug the Kernel and discovered that the restart occurs when the the call to "imx_mipi_regulator_notify" in arch/arm/mach-imx/gpcv2.c is executed, specifically line 777. As I understand it, this call routes the 1.8V on the VDDA_1P8_01/02 pins to the VDDA_PHY_1P8 pin and enables the MIPI PHY. At this point the LDO_1P0D regulator has already been configured and volts are present at the VDDD_1P0_CAP pin.

Scoping the VDDA_PHY_1P8 pin shows the volts begin to rise to approx 280mV. Then the volts decay slightly for approx 1ms before rising to 500mV. This pattern is repeated twice more as the volts get to approx 840mV before the restart occurs.
I have checked for shorts on neighbouring balls and have isolated the MIPI DSI clock and data outputs.

Can anyone please shed any light on what's happening?

I'm using buildroot and the kernel is linux-rel_imx_4.9.x_1.0.0_ga. My device tree and kernel config files are attached.

Thanks for any help

[chris_saunders]

Hello Yuri,

We did notice this so I removed C92 (on MIPI_VREG_0P4V) from the iMX7D dev board and it still boots up without any issues.

Regards

Chris

[Yuri]

Hello,

   The  MIPI_VREG_0P4V capacitor is definitely needed. The fact, that the i.MX7 SABRE looks as working 

without it, may concern some PCB design features.  

Regards,

Yuri.

[Yuri]

Hello,

   perhaps it makes sense to try another board in order to verify if a soldering issue takes place.

Regards,

Yuri.

[chris_saunders]

Hi Yuri,

I have 2 main boards and 2 SOM boards (with the iMX7D on) and the problem is still evident regardless of which combination I try.

Regards,

Chris.

[Yuri]

Hello,

  i.MX7 MIPI_VREG_0P4V  on Your scheme is left floating; on the reference design it is grounded

via 220nF cap.

Regards,

Yuri.

[Yuri]

Hello,

  Is it possible to look at the schematic? 

Regards,

Yuri.

[chris_saunders]

Hi Yuri,

Sorry for the delay in responding.

I can make the schematics available to you if I can have a private email address.

Regards

Chris

[Yuri]

Hello,

  I've sent You mail - just answer it. 

Regards,

Yuri.