Re: [PATCH] target/ppc: Add E500 L2CSR0 write helper

[Bin Meng]

Hi David,

On Wed, Feb 10, 2021 at 9:50 AM David Gibson
<david@gibson.dropbear.id.au> wrote:
>
> On Mon, Feb 08, 2021 at 05:40:58PM +0800, Bin Meng wrote:
> > From: Bin Meng <bin.meng@windriver.com>
> >
> > There are several bits in L2CSR0 (exists in the e500mc/e5500/e6500
> > core) that should be self-cleared when written:
> >
> > - L2FI  (L2 cache flash invalidate)
> > - L2FL  (L2 cache flush)
> > - L2LFC (L2 cache lock flash clear)
> >
> > Add a write helper to emulate this behavior.
> >
> > Signed-off-by: Bin Meng <bin.meng@windriver.com>
>
> IIUC, these are essentially write-only bits - they have some side
> effect when written on real hardware, but won't ever be read back.  Is
> that correct?  Do you have a reference to hardware docs describing
> this behaviour?
>

Please see https://www.nxp.com/files-static/32bit/doc/ref_manual/EREFRM.pdf,
chapter 3.11.2

> I'm assuming that because we don't model the L2 cache, it's ok that
> your implementation just ignores writing these bits, rather than
> performing the cache operations requested?

Yes, guests may read back these bits to confirm the operation is done
by hardware after writing 1 to these bits.

>
> Is that still true for the flash clear operation?

Yes.

>
> > ---
> >
> >  target/ppc/cpu.h                |  6 ++++++
> >  target/ppc/translate_init.c.inc | 16 ++++++++++++++++
> >  2 files changed, 22 insertions(+)
> >

Regards,
Bin