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Re: Qemu mipssim patches, mips malta and virtio bugs

From: Philippe Mathieu-Daudé
Subject: Re: Qemu mipssim patches, mips malta and virtio bugs
Date: Mon, 15 Feb 2021 08:56:07 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0

+Maciej & Laurent (the last time Aleksandar Rikalo made a comment
was 9 months ago).

On 2/15/21 7:39 AM, Thomas Huth wrote:
> On 13/02/2021 14.14, Philippe Mathieu-Daudé wrote:
>> On 2/13/21 11:05 AM, Reinoud Zandijk wrote:
>>> On Fri, Feb 12, 2021 at 10:44:55AM +0100, Philippe Mathieu-Daudé wrote:
>>>>>> i'd like to get the following simple patches to the MIPS/mipssim
>>>>>> target adding
>>>>>> virtio-mmio devices to it.
>>>> Please submit your patches as a series so we can review them on
>>>> the list:
>>>> https://wiki.qemu.org/Contribute/SubmitAPatch#Use_git_format-patch
>>> Oh thanks, i didn't know that; i've created a new patch with the OR
>>> gate you
>>> suggested. We deliberated about the change here and we'll at least
>>> keep it
>>> here locally for testing and profiling code until a real `virt'
>>> platform is
>>> developed for MIPS. Until then it would IMHO be a good expansion to
>>> mipssim.
>>> I'll try to get a proper patch posted on the list :)
>> What I forgot to mention is that QEMU aims to keep models the closer
>> to the hardware, so modifying MIPSsim to some Frankenstein is unlikely
>> to be accepted.
> Well, mipssim never was a real hardware, in fact it is already some kind
> of "virt" machine. So you could theoretically also extend this machine
> instead of introducing a new one (but I'm not a MIPS guy, so no clue
> what makes more sense).

See docs/system/target-mips.rst:

  The mipssim pseudo board emulation provides an environment similar
  to what the proprietary MIPS emulator uses for running Linux. It

  -  A range of MIPS CPUs, default is the 24Kf
  -  PC style serial port
  -  MIPSnet network emulation


  MIPSsim is a proprietary software emulator product of MIPS
  Technologies. It emulates a fairly simple system with two
  8250-class UARTs and a simple network controller. MIPSsim
  consists of several simulators that differ in performance,
  degree of details and debugging features. One for example
  maintains every bit in the system as having three states:
  0, 1 and uninitialized. It's cycle accurate simulator may
  be slow but allows accurate predictors of performance.

  Support status

  MIPSsim support is deprecated and scheduled for removal in
  late 2012 (for the 3.7 release)

  MIPSsim is supported by a stock Linux/MIPS kernel since
  several years. MIPSsim is a proprietary product that is not
  available to the general public. However Qemu supports a
  MIPSsim target as well. That said, MIPSsim is an extremly
  simple platform and virtually everybody is better served by
  the other targets supported by Qemu and the Linux in general.
  At the same time it also appears MIPS Techologies has been
  shifting away from MIPSsim for a while and as such MIPSsim
  support in the kernel is considered obsolete and will
  eventually be removed probably whenever its continued support
  is getting in the way of more useful work.

I doubt MIPS Techologies still has plans for MIPSsim.

Anyhow if we add a virt machine, it does not make sense to use
the NS8250 and MIPSnet devices... We should use the virtio ones.



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