Wait 1ms before issuing the first MRS command to write DDR3 Mode registers.
There is a requirement to wait minimum of Reset CKE Exit time, tXPR, with tXPR = max(tXS, 5tCK) and to wait 500 useconds after reset is de-asserted. It seems that for some reason this is not enforced by the MMDC controller, despite MMDCx_MDOR RST_to_CKE and tXPR being correctly configured.
Without this change we experienced random memory initialization failures with about 2% boot failure rate on specific problematic boards, after this change we were able to do more than 10.000 power-cycle without a single failure.
Fixes: fe0f7f7842e1 ("mx6: add mmdc configuration for MX6Q/MX6DL") Signed-off-by: Francesco Dolcini francesco.dolcini@toradex.com --- arch/arm/mach-imx/mx6/ddr.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/arch/arm/mach-imx/mx6/ddr.c b/arch/arm/mach-imx/mx6/ddr.c index 08e2f0f130a6..7b3d620094c4 100644 --- a/arch/arm/mach-imx/mx6/ddr.c +++ b/arch/arm/mach-imx/mx6/ddr.c @@ -1526,6 +1526,8 @@ void mx6_ddr3_cfg(const struct mx6_ddr_sysinfo *sysinfo, ((sysinfo->ncs == 2) ? 1 : 0) << 30; /* SDE_1 for CS1 */
/* Step 8: Write Mode Registers to Init DDR3 devices */ + mdelay(1); /* Wait before issuing the first MRS command + (tXPR / 500us CKE delay after reset deassertion) */ for (cs = 0; cs < sysinfo->ncs; cs++) { /* MR2 */ val = (sysinfo->rtt_wr & 3) << 9 | (ddr3_cfg->SRT & 1) << 7 |