[PATCH v4 08/12] bloblist: Handle alignment with a void entry

[Raymond Mao]

Hi Ilias,

On Thu, 28 Dec 2023 at 06:32, Ilias Apalodimas <ilias.apalodimas at linaro.org>
wrote:

> Hi Raymond,
>
> On Wed, 27 Dec 2023 at 23:08, Raymond Mao <raymond.mao at linaro.org> wrote:
> >
> > From: Simon Glass <sjg at chromium.org>
> >
> > Rather than setting the alignment using the header size, add an entirely
> > new entry to cover the gap left by the alignment.
> >
> > Signed-off-by: Simon Glass <sjg at chromium.org>
> > Co-developed-by: Raymond Mao <raymond.mao at linaro.org>
> > Signed-off-by: Raymond Mao <raymond.mao at linaro.org>
> > Reviewed-by: Simon Glass <sjg at chromium.org>
> > ---
> >  common/bloblist.c | 23 +++++++++++++++++++----
> >  1 file changed, 19 insertions(+), 4 deletions(-)
> >
> > diff --git a/common/bloblist.c b/common/bloblist.c
> > index 705d9c6ae9..73dbbc01c0 100644
> > --- a/common/bloblist.c
> > +++ b/common/bloblist.c
> > @@ -142,7 +142,7 @@ static int bloblist_addrec(uint tag, int size, int
> align_log2,
> >  {
> >         struct bloblist_hdr *hdr = gd->bloblist;
> >         struct bloblist_rec *rec;
> > -       int data_start, new_alloced;
> > +       int data_start, aligned_start, new_alloced;
> >
> >         if (!align_log2)
> >                 align_log2 = BLOBLIST_ALIGN_LOG2;
> > @@ -151,10 +151,25 @@ static int bloblist_addrec(uint tag, int size, int
> align_log2,
> >         data_start = map_to_sysmem(hdr) + hdr->alloced + sizeof(*rec);
> >
> >         /* Align the address and then calculate the offset from
> ->alloced */
> > -       data_start = ALIGN(data_start, 1U << align_log2) -
> map_to_sysmem(hdr);
> > +       aligned_start = ALIGN(data_start, 1U << align_log2) - data_start;
> > +
> > +       /* If we need to create a dummy record, create it */
> > +       if (aligned_start) {
> > +               int void_size = aligned_start - sizeof(*rec);
> > +               struct bloblist_rec *vrec;
> > +               int ret;
> > +
> > +               ret = bloblist_addrec(BLOBLISTT_VOID, void_size, 0,
> &vrec);
>
> I just noticed the 'BLOBLISTT'. Is that on purpose? or a typo?
>
> > +               if (ret)
> > +                       return log_msg_ret("void", ret);
> > +
> > +               /* start the record after that */
> > +               data_start = map_to_sysmem(hdr) + hdr->alloced +
> sizeof(*vrec);
> > +       }
> >
> >         /* Calculate the new allocated total */
> > -       new_alloced = data_start + ALIGN(size, 1U << align_log2);
> > +       new_alloced = data_start - map_to_sysmem(hdr) +
> > +               ALIGN(size, 1U << align_log2);
>
> So, wouldn't it make more sense to add the dummy record and align the
> whole thing *after* we've added the entry?
> Doing it like this might leave the last entry on an unaligned boundary, no?
>
> The spec just cares about the TE *data* starts at an aligned address but
not the TE header.
Not sure if I fully understand your question but each TE *data* will start
at an aligned address
after calling `bloblist_addrec()`.
And each TE is allowed to have its own alignment value, so we have to do
the padding when
a TE is being added but cannot predict the alignment value for the next TE
- that means we
cannot do the padding after each TE is added.

[...]

Thanks and regards,
Raymond