Re: Deprecate the ppc405 boards in QEMU? (was: [PATCH v3 4/7] MAINTAINERS: Orphan obscure ppc platforms)

[LEROY Christophe]

Le 20/10/2021 à 14:43, Cédric Le Goater a écrit :
> On 10/20/21 13:42, BALATON Zoltan wrote:
>> On Wed, 20 Oct 2021, Philippe Mathieu-Daudé wrote:
>>> On 10/5/21 14:29, Thomas Huth wrote:
>>>> On 05/10/2021 14.20, BALATON Zoltan wrote:
>>>>> On Tue, 5 Oct 2021, Cédric Le Goater wrote:
>>>>>> On 10/5/21 08:18, Alexey Kardashevskiy wrote:
>>>>>>> On 05/10/2021 15:44, Christophe Leroy wrote:
>>>>>>>> Le 05/10/2021 à 02:48, David Gibson a écrit :
>>>>>>>>> On Fri, Oct 01, 2021 at 04:18:49PM +0200, Thomas Huth wrote:
>>>>>>>>>> On 01/10/2021 15.04, Christophe Leroy wrote:
>>>>>>>>>>> Le 01/10/2021 à 14:04, Thomas Huth a écrit :
>>>>>>>>>>>> On 01/10/2021 13.12, Peter Maydell wrote:
>>>>>>>>>>>>> On Fri, 1 Oct 2021 at 10:43, Thomas Huth <thuth@redhat.com>
>>>>>>>>>>>>> wrote:
>>>>>>>>>>>>>> Nevertheless, as long as nobody has a hint where to find that
>>>>>>>>>>>>>> ppc405_rom.bin, I think both boards are pretty useless in
>>>>>>>>>>>>>> QEMU (as far as I
>>>>>>>>>>>>>> can see, they do not work without the bios at all, so it's
>>>>>>>>>>>>>> also not possible
>>>>>>>>>>>>>> to use a Linux image with the "-kernel" CLI option directly).
>>>>>>>>>>>>>
>>>>>>>>>>>>> It is at least in theory possible to run bare-metal code on
>>>>>>>>>>>>> either board, by passing either a pflash or a bios argument.
>>>>>>>>>>>>
>>>>>>>>>>>> True. I did some more research, and seems like there was once
>>>>>>>>>>>> support for those boards in u-boot, but it got removed there a
>>>>>>>>>>>> couple of years ago already:
>>>>>>>>>>>>
>>>>>>>>>>>> https://gitlab.com/qemu-project/u-boot/-/commit/98f705c9cefdf
>>>>>>>>>>>>
>>>>>>>>>>>> https://gitlab.com/qemu-project/u-boot/-/commit/b147ff2f37d5b
>>>>>>>>>>>>
>>>>>>>>>>>> https://gitlab.com/qemu-project/u-boot/-/commit/7514037bcdc37
>>>>>>>>>>>>
>>>>>>>>>>>>> But I agree that there seem to be no signs of anybody actually
>>>>>>>>>>>>> successfully using these boards for anything, so we should
>>>>>>>>>>>>> deprecate-and-delete them.
>>>>>>>>>>>>
>>>>>>>>>>>> Yes, let's mark them as deprecated now ... if someone still 
>>>>>>>>>>>> uses
>>>>>>>>>>>> them and speaks up, we can still revert the deprecation again.
>>>>>>>>>>>
>>>>>>>>>>> I really would like to be able to use them to validate Linux 
>>>>>>>>>>> Kernel
>>>>>>>>>>> changes, hence looking for that missing BIOS.
>>>>>>>>>>>
>>>>>>>>>>> If we remove ppc405 from QEMU, we won't be able to do any
>>>>>>>>>>> regression
>>>>>>>>>>> tests of Linux Kernel on those processors.
>>>>>>>>>>
>>>>>>>>>> If you/someone managed to compile an old version of u-boot for
>>>>>>>>>> one of these
>>>>>>>>>> two boards, so that we would finally have something for
>>>>>>>>>> regression testing,
>>>>>>>>>> we can of course also keep the boards in QEMU...
>>>>>>>>>
>>>>>>>>> I can see that it would be usefor for some cases, but unless 
>>>>>>>>> someone
>>>>>>>>> volunteers to track down the necessary firmware and look after 
>>>>>>>>> it, I
>>>>>>>>> think we do need to deprecate it - I certainly don't have the
>>>>>>>>> capacity
>>>>>>>>> to look into this.
>>>>>>>>>
>>>>>>>>
>>>>>>>> I will look at it, please allow me a few weeks though.
>>>>>>>
>>>>>>> Well, building it was not hard but now I'd like to know what board
>>>>>>> QEMU actually emulates, there are way too many codenames and PVRs.
>>>>>>
>>>>>> yes. We should try to reduce the list below. Deprecating embedded
>>>>>> machines
>>>>>> is one way.
>>>>>
>>>>> Why should we reduce that list? It's good to have different cpu
>>>>> options when one wants to test code for different PPC versions (maybe
>>>>> also in user mode) or just to have a quick list of these at one place.
>>>>
>>>> I think there are many CPUs in that list which cannot be used with any
>>>> board, some of them might be also in a very incomplete state. So
>>>> presenting such a big list to the users is confusing and might create
>>>> wrong expectations. It would be good to remove at least the CPUs which
>>>> are really completely useless.
>>>
>>> Maybe only remove some from system emulation but keep all of them
>>> in user emulation?
>>
>> Or keep them all but mark those that are not tested/may be incomplete? 
>> So the used can see what is expected to work and what may need to be 
>> fixed. That way somebody may try and fix it whereas if it's not there 
>> they are unlikely to try to add it.
> 
> 
> The bamboo machine with 440 CPUs is booting with the latest kernel
> and we have an acceptance test for it now, thanks to Thomas. There
> is not much effort in keeping them in a working state until someone
> volunteers. Hopefully, Christophe is making sure that we are not
> breaking anything with Linux support.
> 
> The 405 machine are still close to deprecation I think. We are still
> struggling to boot one with mainline Linux, using uboot provided by
> Thomas which skips SDRAM init. It is not clear to me if u-boot is
> strictly necessary. It depends if Linux relies on it to do some
> pre-initialization of HW. I guess once we find a good DTS for it, or
> not, we can take a decision.
> 

I now have a hacked configuration booting linux with the hotfoot DTS and 
the kernel is booting up to starting /init

Then it is faulting forever taking a DSI for write protection. The 
problem is now likely in Linux and I'm investigating it, but I'm having 
problem with GDB (7.8.1), I'm hitting the bug 
https://sourceware.org/bugzilla/show_bug.cgi?id=17700

And GDB 11.1 coredumps while reading vmlinux's symbols

Hopefully I'll find a GDB version between 7.8 and 11 that works.