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On Mon, Apr 04, 2022 at 03:39:35PM +0200, Marek Vasut wrote: > On 4/4/22 10:51, Francesco Dolcini wrote: > > 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 > > --- > > 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) */ > > Should we infer this delay from tXPR instead ? I could just delay(tXPR + 500us) and do the exact worst case delay. However I wonder if it is worth doing it, the 1ms delay works in practice, it is big enough to be correct in any case, but small enough not to be a concern on the boot time. Please note that I do not know which timing is violated here (tXPR, the 500us after reset de-assertion or both of them). Francesco