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

[Christophe Leroy]

Le 28/10/2021 à 14:24, Luis Machado a écrit :
> 
> 
> On 10/20/21 10:16 AM, LEROY Christophe wrote:
>>
>>
>> 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.
>>
> 
> Just to confirm, you're not really having problems with the ARM port of 
> GDB, right? It is a 32-bit PowerPC one. The bug you pointed out is only 
> a reference to a similar one for PowerPC?

That's correct, saw the same problem on PowerPC.

I added a comment in bugzilla.

Christophe