Re: [PATCH 00/24] target/riscv: move TCG files and fix --disable-tcg

[Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com>]

On 6/25/2026 6:41 PM, Alistair Francis wrote:
> On Wed, Jun 24, 2026 at 5:18 AM Pierrick Bouvier
> <pierrick.bouvier@oss.qualcomm.com> wrote:
>>
>> On 6/23/2026 12:01 PM, Daniel Henrique Barboza wrote:
>>>
>>>
>>> On 6/23/2026 1:10 PM, Pierrick Bouvier wrote:
>>>> On 6/23/2026 4:38 AM, Daniel Henrique Barboza wrote:
>>>>>
>>>>>
>>>>> On 6/23/2026 6:58 AM, Peter Maydell wrote:
>>>>>> On Tue, 23 Jun 2026 at 10:49, Daniel Henrique Barboza
>>>>>> <daniel.barboza@oss.qualcomm.com> wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 6/22/2026 6:34 PM, Pierrick Bouvier wrote:
>>>>>>>> On 6/22/2026 2:23 PM, Philippe Mathieu-Daudé wrote:
>>>>>>>>> On 22/6/26 22:52, Pierrick Bouvier wrote:
>>>>>>>>>> On 6/22/2026 12:31 PM, Daniel Henrique Barboza wrote:
>>>>>>>>>>> Hello,
>>>>>>>>>>>
>>>>>>>>>>> This series looks scary but it's mostly trivial and mechanical
>>>>>>>>>>> work.
>>>>>>>>>>>
>>>>>>>>>>> It is yet another attempt at fixing --disable-tcg.  We have a
>>>>>>>>>>> recent
>>>>>>>>>>> work sent to the ML [1] and we had Phil's attempt back in 2023
>>>>>>>>>>> [2].
>>>>>>>>>>> Phil's work didn't get merged and it's now too hard to rebase and
>>>>>>>>>>> revive, the most recent attempt got misled into the 'what is
>>>>>>>>>>> common code
>>>>>>>>>>> between TCG and KVM' dungeon.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> It seems like series does not apply on top of master, would that be
>>>>>>>>>> possible to rebase it?
>>>>>>>>>
>>>>>>>>> For some reason the RISC-V series are handled distinctly than the
>>>>>>>>> rest of QEMU, Alistair queues work on his repository and developers
>>>>>>>>> are custome to base their series on top of it (otherwise Alistair
>>>>>>>>> can not apply them on his tree and asks for reposts), see the
>>>>>>>>> riscv-to-apply.next branch on https://github.com/alistair23/qemu.
>>>>>>>>
>>>>>>>> Unfortunately, it makes it hard to run any kind of automated testing,
>>>>>>>> especially for series like this that target specific configs.
>>>>>>>
>>>>>>> Don't we have ways of saying in the commit message "these patches
>>>>>>> applies
>>>>>>> on top of these other patches" and then the tooling would deal with
>>>>>>> it?
>>>>>>> I remember patchew doing stuff like that with that "Based-on:
>>>>>>> <message-id>"
>>>>>>> tag.
>>>>>>
>>>>>> Yes, Based-on: is our convention for marking "this patchset needs some
>>>>>> other one to be applied first". But that should be the exception rather
>>>>>> than a common case -- if patchsets regularly need to be based on
>>>>>> something other than head-of-git, this is I think a sign that
>>>>>> maintainers are not sending out pull requests frequently enough.
>>>>>>
>>>>>> I would prefer it if QEMU didn't develop kernel-style "subsystems
>>>>>> have their own particular workflows" fragmentation -- I don't
>>>>>> think we're big enough or that sub-parts of QEMU are sufficiently
>>>>>> well separated for it to work out well.
>>>>>
>>>>> I agree that rebasing things on master is better than rebasing it on the
>>>>> maintainer's tree.  And we could make a better job at informing
>>>>> developers that
>>>>> submitting a patch for qemu-riscv, vfio or any particular subtree, means
>>>>> that
>>>>> the patch should be based on a maintainer tree X.
>>>>>
>>>>> The thing is that sending patches on master only works if master is
>>>>> always up
>>>>> to date, and that's not feasible with our current style of merging PRs.
>>>>> This
>>>>> series we're commenting on is an example: it doesn't apply to master
>>>>> because
>>>>> there are pre-approved RISC-V patches in the maintainer's tree from 2
>>>>> days ago
>>>>> (also my patches, I might add) that caused conflicts that I wasn't aware
>>>>> that
>>>>> would happen.  This conflict would have to be dealt with at some point
>>>>> by myself
>>>>> or the maintainer, and it's not like 2 days is too much time without
>>>>> a PR.
>>>>>
>>>>> We can argue "this is an exception that doesn't happen that often, we
>>>>> should
>>>>> stick with using master as a base", and to a certain extend that's
>>>>> true.  But
>>>>> then this sort of conflict happens again, then again, then again, it
>>>>> comes to
>>>>> a point where it's easier to tell developers to use the maintainer's
>>>>> tree instead
>>>>> of master.
>>>>>
>>>>> Maybe I'm downplaying the problem because I've been sending stuff based
>>>>> on the
>>>>> maintainer's tree since forever and got used to it.  IMO, unless we
>>>>> decide to be
>>>>> like libvirt and create the "committer" role to allow trustworthy devs
>>>>> to push
>>>>> stuff to master after acks, making it more feasible to expect master to
>>>>> be up to
>>>>> date, I'm afraid we're closer to a kernel-style workflow.  For better or
>>>>> worse.
>>>>>
>>>>>
>>>>> Thanks,
>>>>> Daniel
>>>>>
>>>>>
>>>>>>
>>>>>> thanks
>>>>>> -- PMM
>>>>>
>>>>
>>>> In this very specific case, where base patches are needed, maybe it
>>>> would be better to make the required commits appear in this series, and
>>>> mention in cover letter that patches 1-N are just coming from another
>>>> series and are already reviewed/approved. IMHO it doesn't hurt, and
>>>> reviewers are free to skip commits already reviewed.
>>>
>>> That's fair enough but I wonder if that won't scare people away with
>>> even bigger series :D  in this case here I would need to either send all
>>> the queued patches, making the series go to 40+, or I would need to triage
>>> which patches from the queue creates a conflict with this work and send
>>> only those.
>>>
>>> Now, as for qemu-ci ...  How farfetched it is to make it read a specific
>>> tag
>>> in the cover-letter, e.g. "branch-id", that can point to a gitlab/github
>>> repo with the patches, and use that code base instead of applying the
>>> patches to the master branch?  Then for the next version of this work
>>> I could do
>>>
>>> "branch-id: https://gitlab.com/danielhb/qemu/-/tree/riscv_disabletcg_v2"
>>>
>>
>> Based-on: is a QEMU specific tag, that is only understood by patchew,
>> and no other tool to my knowledge.
>> b4 has base_commit, which allows to give a specific base, but not a
>> specific repository. I'm not aware of any b4 tag that allows to mention
>> a base series. It makes sense, series are not branches, and stacking
>> them comes with a lot of problems.
>>
>> So it seems like email workflow is quite limited in this regard, and the
>> only way to deal with it properly is to wait for base patches to be
>> merged, or include them in the series.
>>
>> From another perspective, the same problem would exist if we would use a
>> forge like GitHub or GitLab. It's not possible to stack PR on top of
>> others, and only solution is to wait, or duplicate patches. IMHO, it's a
>> sane default, as it forces correct ordering instead of allowing chaotic
>> development.
>>
>>> and the tool would still work.  If there's no "branch-id" then it assumes
>>> that the patches are to be applied on master.
>>>
>>>
>>> And yeah, in an ideal world the problem goes away if we just do more PRs
>>> and
>>> strive to keep 'master' updated.  I'm just thinking out loud about possible
>>> alternatives until we reach that point.
> 
> When you sent v2 of this series it had been one week since the last
> RISC-V PR. Are we really aiming for more than one PR a week?
> 
>>>
>>>
>>> Cheers,
>>> Daniel
>>>
>>>>
>>>> Or, a solution I'm not fond of but I ended up adopting most of the time,
>>>> just wait for required patches to be merged on master before posting the
>>>> series, and work on something else meanwhile.
> 
> I do feel that a few people do that, just not Daniel :)
>

Waiting works well if you know the wait period is deterministic. "Ok, I
missed this train, let me catch the one next week". Unfortunately, it
varies per maintainer, and some are even stochastic processes on their own.

I can't blame people who submit and are not maintainer to feel
frustration with this, it's a real issue.

> Alistair
> 
>>>>
>>>> Ideally, yes, it would be better if maintainers could send PR more
>>>> frequently to avoid creating those intermediate staging trees. The
>>>> faster we merge, the less conflicts we'll have.
>>>>
>>>> Regards,
>>>> Pierrick
>>>
>>
>>