[lkml]   [2020]   [Aug]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 00/13] MIPS: Convert Ingenic to a generic board
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.

> > 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.


 \ /
  Last update: 2020-08-22 04:31    [W:0.081 / U:4.444 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site