svn commit: r298477 - in head/sys: conf riscv/riscv

[Ian Lepore]

On Fri, 2016-04-22 at 23:31 +0200, Marko Zec wrote:
> On Fri, 22 Apr 2016 16:15:59 +0000
> Ruslan Bukin <br at freebsd.org> wrote:
> 
> > Author: br
> > Date: Fri Apr 22 16:15:58 2016
> > New Revision: 298477
> > URL: https://svnweb.freebsd.org/changeset/base/298477
> > 
> > Log:
> >   Clear the DDR memory. This should be done by bootloaders,
> >   but they have no such feature yet.
> >   
> >   This fixes operation on Rocket Core and lowRISC.
> > 
> > Modified:
> >   head/sys/conf/options.riscv
> >   head/sys/riscv/riscv/locore.S
> > 
> > Modified: head/sys/conf/options.riscv
> > ==============================================================================
> > --- head/sys/conf/options.riscv> > 	> > Fri Apr 22 15:12:05
> > 2016> > 	> > (r298476) +++ head/sys/conf/options.riscv> > 	> > Fri Apr
> > 22 16:15:58 2016> > 	> > (r298477) @@ -2,3 +2,4 @@
> >  
> >  RISCV> > 	> > 	> > 	> > 	> > opt_global.h
> >  VFP> > 	> > 	> > 	> > 	> > opt_global.h
> > +DDR_CLEAR_SIZE> > 	> > 	> > 	> > opt_global.h
> > 
> > Modified: head/sys/riscv/riscv/locore.S
> > ==============================================================================
> > --- head/sys/riscv/riscv/locore.S> > 	> > Fri Apr 22 15:12:05
> > 2016> > 	> > (r298476) +++ head/sys/riscv/riscv/locore.S> > 	> > Fri
> > Apr 22 16:15:58 2016> > 	> > (r298477) @@ -126,6 +126,17 @@ _start:
> >  > > 	> > csrr> > 	> > a0, mhartid
> >  > > 	> > bnez> > 	> > a0, mpentry
> >  
> > +#if defined(DDR_CLEAR_SIZE)
> > +> > 	> > /* Clear DDR memory */
> > +> > 	> > la> > 	> > t0, _end
> > +> > 	> > li> > 	> > t1, DDR_CLEAR_SIZE
> > +1:
> > +> > 	> > sd> > 	> > zero, 0(t0)
> > +> > 	> > addi> > 	> > t0, t0, 8
> > +> > 	> > bltu> > 	> > t0, t1, 1b
> 
> Usually _end appears to be (double) word aligned, but that happens out
> of pure luck, since compilers do not provide firm guarantees about
> _end's alignment (at least gcc doesn't, as far as I know).
> 
> So depending on which kind of RV this code would run, sometimes it may
> end up doing a lot of traps emulating unaligned access in software, or
> worse...
> 
> Hence it would't hurt to check for _end's alignment first and do a few
> byte-by-byte bzero()ing if needed, before proceeding a dword pace.
> 
> 

All of our kernel linker scripts ensure that _end is aligned correctly
for the platform, except powerpc and powerpc64.  I'm not sure if it's
just not required for those, or maybe it's an oversight that has been
harmless so far.

-- Ian