Messages in this thread | | | Subject | Re: [RESEND in plain-test] Re: [PATCH v5 0/9] Add initial support for the i.MXRTxxxx SoC family starting from i.IMXRT1050 SoC. | From | Giulio Benetti <> | Date | Fri, 17 Dec 2021 10:54:39 +0100 |
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Hi Arnd,
On 16/12/21 22:13, Arnd Bergmann wrote: > On Thu, Dec 16, 2021 at 6:33 PM Giulio Benetti > <giulio.benetti@benettiengineering.com> wrote: >> On 16/12/21 09:26, Arnd Bergmann wrote: >>> On Wed, Dec 15, 2021 at 11:05 PM Jesse Taube <mr.bossman075@gmail.com> wrote: > >>> As a more general comment, it's always nice to see newly added SoC >>> platforms, especially when they are this well implemented and done >>> by hobbyists. However, I do think you are being overly optimistic >>> as to how useful this is going to be to other people: interest in NOMMU >>> ARM platforms has dropped a lot over the past 5 years, and as far as I >>> can tell, it is only being kept alive for existing stm32 customers >>> as the economics do not favor Linux on Cortex-M for new products >>> compare to Linux on Cortex-A or some RTOS on Cortex-M. >>> >>> The existing users will inevitably stop updating their kernels at some >>> point, and then it's most likely just you and Vladimir Murzin that care. >> >> >> About this will you accept support for the other SoCs in the family? >> We would like to add in the near future: >> - i.MXRT1020(uboot support is already upstreamed) >> - i.MXRT1024(almost equal to 1020) >> - i.MXRT1060(almost equal to 1050) >> - i.MXRT1064(almost equal to 1060) >> And >> - i.MXRT1160/70 new family with faster core clock(1Ghz) and a cortex M4 >> >> We need to add missing lcd(uboot upstreamed), usb(uboot upstreamed), >> ethernet(wip) supports for i.MXRT10xx family. > > Sure, anything you want to work on supporting can be added to the kernel, > the important bit is that it's well written and can be maintained going forward. > > My best guess is that we'll end up ripping out all NOMMU support in > a few years, when we get to a point when both of these things happen: > > - the number of actual users that still update their kernels becomes > really low > > - There is some treewide refactoring that isn't easily supportable without an > MMU unless someone puts extra work into it. > > At the moment, we still support NOMMU kernels on a bunch of architectures > (Arm, riscv/k210, sh/j2, m68k/coldfire, xtensa and h8300). Out of these, > Arm is by far the most active, and if Arm NOMMU support was to go away > for some reason, the others would likely follow.
Ok, I understad now.
>> This is to organize with Jesse also about buying evaluation boards and >> timing. >> >> We’ve meant this porting also as an exercise to deal with Linux deeper >> for us and for the other newbies. >> >> We’ve been also asked about a possible support for s32s(quad cortex-R52) >> on initial emails but it has no mmu too. >> While I’m seeing that some cortex-R is landing inside Linux. >> Would it be interesting anyway? > > I brought that up during the initial review, but I think this is even > less interesting > than Cortex-M support from the perspective of potential use cases. While > Cortex-M MCUs have some advantages over larger SoCs in terms of > power consumption and cost, this is generally not true for running Linux > on Cortex-R. The Cortex-R and Cortex-A cores are closely related, so > they tend have similar power/performance/area characteristics, but > the lack of an MMU makes the Cortex-R much less useful. If there was > an advantage to running with the MMU disabled, you could actually do that > on a Cortex-A as well, but clearly nobody does that either.
Yes
Thank you for the answer
> Vladimir has put some work into making Cortex-R work in the kernel, and > he may have some other thoughts on this question.
I'm curious if he has something specific to Cortex-R to tell.
I've found that Cortex-R82 has a MMU: https://www.arm.com/products/silicon-ip-cpu/cortex-r/cortex-r82 but I can't find any SoC that uses it. Also, I don't know how many people could use it honestly.
Best regards -- Giulio Benetti Benetti Engineering sas
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