Am Fri, 11 Nov 2016 13:53:16 +0100 schrieb Nico Huber <[email protected]>:
> Hi Charlotte, > > On 11.11.2016 08:14, Charlotte Plusplus wrote: > > So I did many more tests today (more than 6h, and flashing around 30 > > times), with SPD settings hardcoded into raminit, and without the > > mrc cache interfering. > > thanks for the analysis and summing this up. > > > > > TLDR: coreboot tries to increase the frequency without increasing > > the voltage, and that doesn't work for all memory. > > > > Basically, with the problematic ram sticks, I can boot perfectly > > fine at DDR3-1866 speed, but even the slower setting 11-11-11-31 > > gives errors on the memtest. This is inconsistent with information > > I found about my memory from its SPD information, and from other > > people who overclock this exact same memory. > > > > Even at 10-10-10-27, I still get errors at DDR3-1600 speeds. Far > > fewer than before, but some errors sill. > > > > After reading more about XMP and SPD, it is my understanding that : > > - JEDEC specs stop at 1600, and after that XMP is required > > - even before 1600, XMP also offers profiles, and they are not > > optional: some memory is otherwise unable to work at its advertised > > speed > > This would mean the memory is just broken. But that's what I suspect > of any memory that's supposed to run out of spec. > Yes XMP is required to run "out of spec". That's why all Intel Processors only advertise DDR3-1600 as maximum frequency on Intel's homepage. XMP is optional. I don't think that XMP is the problem. My guess is that raminit doesn't set all required registers to fine tune the memory controller to get it stable. > > - XMP profiles are some kind of overclocking: they usually require > > adjusting the voltage, to deal with this increased speed > > Not kind of overclocking, simply overclocking. There's only one > voltage specified for DDR3, IIRC. > > > - in XMP profile bytes, voltage increase information is given > > precisely > > - nowhere in the code I saw anything increasing the voltage, while > > XMP requires that > > > > I conclude that while there may be errors in selecting the SPD > > settings, even if the SPD is manually corrected with known-good > > settings, or if overshooting with very generous latencies, some > > errors do remain as the ram is being asked to operate outside its > > voltage specifications (given the frequency) > > > > 1.5V is a JEDEC spec, but RAM is advertised based on the information > > contained in the XMP profiles, which at the moment do not seem fully > > supported. > > JEDEC is the standard. If the XMP support is half-baked it should be > disabled by default. Maybe we should even put a warning in the log if > we encounter an XMP profile with anything else than 1.5V (if it's > common that those DIMMs are broken ex factory). > Yes, we could add a warning that XMP profile will be used. I personly never had problems with it. > > > > I do not know how to adjust the voltage (it should require talking > > to the IMC of the CPU) but I think that as soon as this is done, > > stability should improve. > > > > If someone can propose a patch doing that (either using the voltage > > read from SPD, or by manually entering voltage information), I will > > be happy to test it. > > Depending on the board the voltage might not be configurable at all. > Why should it be if there is only one voltage defined in the standard? > The W520 does only have 1.5V DDR voltage. If it's stable with vendor bios, it's not a DDR voltage problem at all. > > > > For now, I urge caution when operating even at DDR-1866 > > frequencies. Most boards do set up 933 as their max_mem_clock_mhz. > > It is not very prudent to do that until the voltage situation can > > be solved. > > If the board can work at that frequency, that's just fine. If the > voltage is a problem, it's due to the memory module. IMHO, the rule > should be to ignore SPD frequency settings that include an out of spec > voltage. That's what sandybridge raminit does. Only XMP profiles with DDR voltage of 1.5V are used. Profiles that do have other voltage setting are ignored. Regards, Patrick > > If you want to do further testing, you can try to find out which com- > binations of processor and DIMMs work with the Vendor BIOS or the MRC > blob (I wouldn't expect that it supports non-JEDEC stuff, but it would > be nice to know if something can be fixed in coreboot easily). > > Nico -- coreboot mailing list: [email protected] https://www.coreboot.org/mailman/listinfo/coreboot
