Messages in this thread | | | Date | Sat, 22 Aug 2020 15:17:49 +0200 | From | Paul Cercueil <> | Subject | Re: [PATCH 00/13] MIPS: Convert Ingenic to a generic board |
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Le sam. 22 août 2020 à 3:29, Maciej W. Rozycki <macro@linux-mips.org> a écrit : > Hi Paul, > >> > FAOD <cpu-feature-overrides.h> is not a hack, but an optimisation >> measure >> > so that features known to be hardwired for a given machine/CPU do >> not have >> > to be dynamically queried every time referred. In some cases >> that results >> > in large portions of code being optimised away by the compiler as >> well. >> >> Fair enough. Bloat-o-meter reports about ~100 KiB saved when that >> file is >> present. But we can't use it in a generic kernel, unfortunately. > > Well, run-time patching might be an alternative to get the best of > both > worlds, but someone would have to reimplement our feature selection > system > to use it.
Would run-time patching allow to drop dead code?
>> > The hardcoded value for a feature defined in >> <cpu-feature-overrides.h> >> > always has to be the same as one in the corresponding bit of the >> `options' >> > member of `struct cpuinfo_mips', in this case MIPS_CPU_TLBINV. >> >> In theory yes, in practice the CPU detection code is lagging >> behind... > > I wasn't aware of that. In that case it has been a design abuse > which > has been missed by the maintainer when accepting patches. It used to > be > the case that run-time detection was accurate and overrides were > rather > lazily added. > > Also I note Ingenic must have had a CPU erratum if our > `decode_configs' > doesn't just work, as the interpretation of CP0.Config[5:0] registers > has > been architectural and mandatory, and that for a reason. It's only > legacy > MIPS I-IV processors that should require special attention here.
Yes, Ingenic CPUs have a few bloopers here and there...
-Paul
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