Re: [PATCH 5/9] kern/ieee1275/init: ppc64: Add support for alignment requirements

[Stefan Berger]

On 11/10/23 08:09, Hari Bathini wrote:
> On 31/10/23 11:20 pm, Stefan Berger wrote:
> > Add support for memory alignment requirements and adjust a candidate
> > address to it before checking whether the block is large enough. This
> > must be done in this order since the alignment adjustment can make a
> > block smaller than what was requested.
> >
> > None of the current callers has memory alignment requirements but the
> > ieee1275 loader for kernel and initrd will use it to convey them.
> >
> > Signed-off-by: stefan Berger <stefanb@linux.ibm.com>
> > Cc: Hari Bathini <hbathini@linux.ibm.com>
> > Cc: Pavithra Prakash <pavrampu@in.ibm.com>
> > Cc: Michael Ellerman <mpe@ellerman.id.au>
> > Cc: Carolyn Scherrer <cpscherr@us.ibm.com>
> > Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
> > Cc: Sourabh Jain <sourabhjain@linux.ibm.com>
> > ---
> >   grub-core/kern/ieee1275/init.c        | 14 ++++++++++++++
> >   include/grub/powerpc/ieee1275/alloc.h |  1 +
> >   2 files changed, 15 insertions(+)
> >
> > diff --git a/grub-core/kern/ieee1275/init.c 
> > b/grub-core/kern/ieee1275/init.c
> > index a0ce9d55e..542a4c595 100644
> > --- a/grub-core/kern/ieee1275/init.c
> > +++ b/grub-core/kern/ieee1275/init.c
> > @@ -506,6 +506,20 @@ regions_claim (grub_uint64_t addr, grub_uint64_t 
> > len, grub_memory_type_t type,
> >               }
> >           }
> >       }
> > +
> > +  /* Honor alignment restrictions on candidate addr */
> > +  if (rcr->align)
> > +    {
> > +      grub_uint64_t align_addr = ALIGN_UP (addr, rcr->align);
> > +      grub_uint64_t d = align_addr - addr;
> > +
> > +      if (d > len)
> > +        return 0;
> > +
>
> > +      len -= d;
>
> Curious.. Is 'len' here length of the region or the claim request size?

len is the length of the requested size of a memory region

> If latter, why should 'len' have any impact here??
>
> Thanks
> Hari