Re: [PATCH 0/7] hw/mips/malta: Rework to allow more than 2GB of RAM on 64-bit

[Philippe Mathieu-Daudé]

On 6/30/20 1:17 PM, Aleksandar Markovic wrote:
> уторак, 30. јун 2020., Philippe Mathieu-Daudé <f4bug@amsat.org
> <mailto:f4bug@amsat.org>> је написао/ла:
> 
>     On 6/30/20 1:01 PM, Aleksandar Markovic wrote:
>     >
>     >
>     > уторак, 30. јун 2020., Philippe Mathieu-Daudé <f4bug@amsat.org
>     <mailto:f4bug@amsat.org>
>     > <mailto:f4bug@amsat.org <mailto:f4bug@amsat.org>>> је написао/ла:
>     >
>     >     On Tue, Jun 30, 2020 at 12:52 PM Philippe Mathieu-Daudé
>     >     <f4bug@amsat.org <mailto:f4bug@amsat.org>
>     <mailto:f4bug@amsat.org <mailto:f4bug@amsat.org>>> wrote:
>     >     >
>     >     > On 6/30/20 12:48 PM, Aleksandar Markovic wrote:
>     >     > >
>     >     > >
>     >     > > уторак, 30. јун 2020., Philippe Mathieu-Daudé
>     <f4bug@amsat.org <mailto:f4bug@amsat.org>
>     >     <mailto:f4bug@amsat.org <mailto:f4bug@amsat.org>>
>     >     > > <mailto:f4bug@amsat.org <mailto:f4bug@amsat.org>
>     <mailto:f4bug@amsat.org <mailto:f4bug@amsat.org>>>> је написао/ла:
>     >     > >
>     >     > >     Hi,
>     >     > >
>     >     > >     Following Jiaxun Yang's patch and discussion:
>     >     > >     https://patchwork.kernel.org/patch/11416915/
>     <https://patchwork.kernel.org/patch/11416915/>
>     >     <https://patchwork.kernel.org/patch/11416915/
>     <https://patchwork.kernel.org/patch/11416915/>>
>     >     > >     <https://patchwork.kernel.org/patch/11416915/
>     <https://patchwork.kernel.org/patch/11416915/>
>     >     <https://patchwork.kernel.org/patch/11416915/
>     <https://patchwork.kernel.org/patch/11416915/>>>
>     >     > >
>     >     > >     - Rename the current machine as 'malta-virt' (keeping
>     >     'malta' aliased)
>     >     > >       Suggestions for better names are welcome, maybe
>     >     'malta-unreal' or
>     >     > >       'malta-unleashed' instead?
>     >     > >     - Add 'malta-phys' which respects hardware
>     restrictions (on
>     >     RAM so far)
>     >     > >     - Unleash 'malta-virt' to allow more than 2GB on 64-bit
>     >     > >
>     >     > >     Philippe Mathieu-Daudé (7):
>     >     > >       hw/mips/malta: Trivial code movement
>     >     > >       hw/mips/malta: Register the machine as a TypeInfo
>     >     > >       hw/mips/malta: Rename 'malta' machine as 'malta-virt'
>     >     > >       hw/mips/malta: Introduce MaltaMachineClass::max_ramsize
>     >     > >       hw/mips/malta: Introduce the 'malta-phys' machine
>     >     > >       hw/mips/malta: Verify malta-phys machine uses
>     correct DIMM
>     >     sizes
>     >     > >       hw/mips/malta: Allow more than 2GB on 64-bit malta-virt
>     >     > >
>     >     > >      hw/mips/malta.c | 121
>     >     +++++++++++++++++++++++++++++++++++++++---------
>     >     > >      1 file changed, 99 insertions(+), 22 deletions(-)
>     >     > >
>     >     > >     --
>     >     > >
>     >     > >
>     >     > >
>     >     > > Thank you, Philippe, for providing this series.
>     >     > >
>     >     > > However, in previous discussion on the patch you mention
>     above, I
>     >     > > already expressed serious reservations on the approach
>     taken in that
>     >     > > patch. These reservations stay today too.
>     >     > >
>     >     > > There is nothing qualitatively different between the original
>     >     patch and
>     >     > > this series. Naming and related stuff are just cosmetic
>     issues.
>     >     >
>     >     > OK, what about considering all patches except the last one?
>     >     > So we can run firmware on a real Malta board, not the QEMU
>     >     > imaginary one (in the discussion you said QEMU should respect
>     >     > real hardware, which I agree).
>     >     >
>     >     > >
>     >     > > The good thing about this series is that one can apply it
>     >     dowstream, if
>     >     > > one finds it useful. However, it is not suitable for
>     upstreaming
>     >
>     >     IOW, what is missing to have this series (except the last patch)
>     >     accepted upstream?
>     >
>     >
>     > It is not what is missing, but was already is in the series that makes
>     > it not suitable for upstreaming. The very concept of the series is
>     > problematic.
> 
>     What is the series is not suitable for upstream? Can you point to
>     patch and code please? How would you conceptually resolve the
>     problem?
> 
> 
> The answer is already in the original thread on the original patch.
> 
> The problem is artificialy imposed:
> 
> One needs a feature not present in the physical system. The solution is
> not in creating "virtual" upgrade - this violates the basic foundation
> if QEMU.
> 
> If the feature is missing, the optimal solution would be emulating the
> physical solution that has that feature.
> 
> In some rare cases (that should be avoided as mush as possible), and for
> really good reasons, we can create an emulation of some imagined
> hardware that was never designed let alone built - there are a couple of
> examples in other targets.
> 
> But extending the emulation of existing physical system with
> non-existing features is not acceptable.
> 
> Hopefuly everything is clear now to you. :)

I guess I understand a bit. I was confused by your use of "upstream".
It seems you use it the wrong way, so for you "upstream" is what the
MIPS enterprise world wants/needs, while "downstream" is what the
open-source community wants/needs.

If MIPS enterprise doesn't want a Malta machine model with 3GB of RAM,
they can disable it in their downstream.
If it helps the upstream community, the model is wrong anyway by using
2GB. It would be disastrous for all user to restrict the malta machine
to 1GB upstream.

> 
> Regards,
> Aleksandar
> 
>  
> 
>     >
>     > Regards,
>     > Aleksandar
>     >
>     >
>     >
>     >
>     >
>     >  
>     >
>     >     > >
>     >     > > Regards,
>     >     > > Aleksandar
>     >     > >
>     >     > >
>     >     > >
>     >     > >     2.21.3
>     >     > >
>     >
>