Message-ID: <8c4a4114-b7f7-301e-20b8-960e6234b661@linaro.org>
Date:   Tue, 3 Oct 2017 10:12:02 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Sudeep Holla <sudeep.holla@....com>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Liviu Dudau <liviu.dudau@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, patches@...aro.org
Subject: Re: [PATCH v2] arm64: dts: foundation-v8: Enable PSCI mode

On 02/10/17 18:26, Sudeep Holla wrote:
> Sorry for late response, I thought I had sent this mail out long back
> but was sitting in my draft :(

No worries. I've been at Linaro connect this last week anyway.


> On 20/09/17 12:17, Daniel Thompson wrote:
>> On 20/09/17 10:42, Sudeep Holla wrote:
>>>
>>>
>>> On 19/09/17 19:32, Daniel Thompson wrote:
>>>> Currently if the Foundation model is running ARM Trusted Firmware then
>>>> the kernel, which is configured to use spin tables, cannot start
>>>> secondary
>>>> processors or "power off" the simulation.
>>>>
>>>> After adding a couple of labels to the include file and splitting out
>>>> the
>>>> spin-table configuration into a header, we add a couple of new headers
>>>> together with two new DTs (GICv2+PSCI and GICv3+PSCI).
>>>>
>>>> The new GICv3+PSCI DT has been boot tested, the remaining three (two of
>>>> which existed prior to this patch) have been "tested" by decompiling the
>>>> blobs and comparing them against a reference.
>>>>
>>>
>>> How different are these from the ones hosted in [1] ?
>>
>> They look like they were either independently written or diverged a long
>> time ago. The existing kernel DTs describe hardware absent from the ARM
>> TF ones and vice versa.
>>
> 
> OK.
> 
>> With specific reference to PSCI it looks like my patches could perhaps
>> be improved by adding idle-state support.
> 
> Yes I know.

You want a v3 with it added?


>>> On argument is that we want to take the DTS out of device tree as
>>> firmware is responsible for generating them. Alternatively, we may be
>>> duplicating resulting in discrepancies over time by coping it into
>>> kernel.
>>
>> The general problem is copying from where?
>>
>> The kernel DTs are a well maintained centralized repository which is
>> *really* useful. git grep across the kernel DTs is a hugely powerful
>> tool when trying to better understand an ecosystem as sprawling and
>> diverse as ARMs. In fact I've even seen those sort of searchs used as a
>> basis to clean up unused code. Seeing that centralized repository
>> splinter into separate per-vendor silos would be a huge loss for kernel
>> developers.
>>
> 
> Agreed. But models are configurable and last time this discussion came
> up, some argued that the DTs must be modified based on the configuration
> automatically by models or some external scripts.

Indeed. I can definitely understand why the *models* might want
to be bundled with DTs (or a DT generator, or a
--just-give-me-a-working-dt-for-my-command-line-options-option).


>> <snip>
>> In other words, whilst people could discuss alternative ways to manage
>> DTs[1], I can't see any universe where ARM TF would be a logical place
>> to keep them.
>>
>> [1] ... and I'd further suggest that only perhaps people who are
>>      prepared to put resources into fixing it should convene such a
>>      discussion.
> 
> While I agree with you, I am worried on the scalability. Models provide
> tons of options(may not be foundation platform but for sure the base AEM
> ones). It may so get unmanageable if we keep adding one DTS per
> configuration.
> 
> If we are OK restricting the set of configurations to what you have
> proposed, then it seems fine.
> 
> I will try to push this for v4.15, but I still want to hear more
> opinions on the scalability part here.

I'm sure you mean other peoples opinions ;-) (especially so, since after 
reading things back, I realized I expressed mine rather more forefully 
than intended) but I think there is a reason why PSCI is special... 
basically its to do with the docs.

I figured out how to use foundation model by reading the documentation. 
That documentation says "to run Linux go read the Linaro stuff". As it 
happens the Linaro "stuff" loops you through to a different ARM doc 
which tells you how to download ARM TF and bootloader binaries from 
Linaro. Thus if you follow the docs (and are patient enough) you come 
out the other side with a model running ARM TF and ready for PSCI.

At that point you're ready for mainline kernel development... and you 
wonder why there is only one CPU running ;-).


Daniel.

Powered by blists - more mailing lists