iMX7 cannot enter LPSR when M4 core is active

[senthilkumarcha]

Hi,

We are using a custom board with imx7d processor. We have implemented LPSR mode which is working fine when M4 core is disabled. If M4 core is active, the device enters Deep sleep mode(DSM) instead of LPSR mode when "echo mem > /sys/power/state" command is used.
Then I have noted that there are some conditions in pm-imx7.c which does not allow the device to enter LPSR mode when M4 is in RUN state.

if ((!imx_src_is_m4_enabled()) ||

   (imx_src_is_m4_enabled() && imx_mu_is_m4_in_stop()))
      imx_gpcv2_mf_mix_off();;

and 

if (imx_gpcv2_is_mf_mix_off()) {

/* LPSR implementation */
}

So I have disabled the conditions. After that I can enter LPSR mode and wake up from LPSR mode. But M4 core reboots instead of resumes from the previous state after waking up from LPSR mode.

My queries are

i) Why cant device enter LPSR mode when M4 is active ?

ii) Can we put M4 core in STOP mode from A7 core ?

iii) Can M4 resumes from its previous state after LPSR mode?

Thanks in Advance,

C.Senthilkumar

[Bio_TICFSL]

Hi Chandran,

In LPSR mode, M4 power rail is off, it can't stay at suspend mode.

[senthilkumarcha]

Hi @Bio_TICFSL,

Thanks for the reply.

Can we restore the state of M4 core after resuming from LPSR mode like A7 core? i.e by storing the current state in LPDDR3 and retrieve it after resumes.

Thanks in Advance,

C.Senthilkumar