Re: [PATCH] hw/ppc/e500: Partial implementation of local access window registers

[BALATON Zoltan]

On Sun, 2 Mar 2025, Bernhard Beschow wrote:
> Am 1. März 2025 16:10:35 UTC schrieb BALATON Zoltan <balaton@eik.bme.hu>:
> > On Wed, 15 Jan 2025, BALATON Zoltan wrote:
> > > This allows guests to set the CCSR base address. Also store and return
> > > values of the local access window registers but their functionality
> > > isn't implemented.
> >
> > Bernhard,
>
> Hi Zoltan,
>
> > If you have no alternative patch you plan to submit for next release 
> > should we merge this for now? This helps running u-boot binaries even 
> > if it's not enough alone but would be one patch less in my local tree. 
> > Or do you know about a problem with this patch why this should not be 
> > merged?
>
> QEMU sets a machine-specific CCSR base address (pmc->ccsrbar_base) which 
> differs from the real chip's default. The default is checked by U-Boot 
> which enters an infinite loop on mismatch: 
> <https://source.denx.de/u-boot/u-boot/-/blob/v2024.07/arch/powerpc/cpu/mpc85xx/start.S#L614>. 
> How does this work for you?

The U-Boot version I've tested (or something else, I don't remember) 
wanted to set the CCSRBAR to the value it expects which is different from 
where it looks for it at reset and that works with this patch. I don't 
know which code path that corresponds to in start.S.

> In addition, when moving the CCSR region, `env->mpic_iack` should be 
> updated as well: 
> <https://gitlab.com/qemu-project/qemu/-/blob/v9.2.2/hw/ppc/e500.c?ref_type=tags#L969>

I did not notice that. Maybe it's only relevant with KVM and I've only 
tested with TCG or could be I did not get to the part yet when this would 
cause problems. I don't see an easy way to update this as these are in 
separate places and also don't know how this mpic_iack is handled with 
multiple cores. So in case this patch breaks this then it's OK to drop it 
for now. I can carry it locally until fixed upstream.

> I'm happy to submit an implementation on top of my e500 cleanup series 
> <https://patchew.org/QEMU/20241103133412.73536-1-shentey@gmail.com/> 
> which needs agreement on some open discussions.

Some of that series was already merged. What are the outstanding patches 
and discussions? I don't remember seeing an updated version of that series 
with only the outstanding patches.

Regards,
BALATON Zoltan