linux-kernel - Re: [PATCH] of: unittest: Statically apply overlays using fdtoverlay

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Date:   Tue, 12 Jan 2021 12:17:25 -0600
From:   Frank Rowand <frowand.list@...il.com>
To:     Bill Mills <bill.mills@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        anmar.oueja@...aro.org, Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH] of: unittest: Statically apply overlays using fdtoverlay

On 1/12/21 4:16 AM, Bill Mills wrote:
> 
> 
> On 1/12/21 3:37 AM, Viresh Kumar wrote:
>> On 11-01-21, 20:22, Bill Mills wrote:
>>> On 1/11/21 5:06 PM, Frank Rowand wrote:
>>>> NACK to this specific patch, in its current form.
>>>>
>>>> There are restrictions on applying an overlay at runtime that do not apply
>>>> to applying an overlay to an FDT that will be loaded by the kernel during
>>>> early boot.  Thus the unittest overlays _must_ be applied using the kernel
>>>> overlay loading methods to test the kernel runtime overlay loading feature.
>>>>
>>>> I agree that testing fdtoverlay is a good idea.  I have not looked at the
>>>> parent project to see how much testing of fdtoverlay occurs there, but I
>>>> would prefer that fdtoverlay tests reside in the parent project if practical
>>>> and reasonable.  If there is some reason that some fdtoverlay tests are
>>>> more practical in the Linux kernel repository then I am open to adding
>>>> them to the Linux kernel tree.
>>
>> I wasn't looking to add any testing for fdtoverlay in the kernel, but
>> then I stumbled upon unit-tests here and thought it would be a good
>> idea to get this built using static tools as well, as we aren't
>> required to add any new source files for this and the existing tests
>> already cover a lot of nodes.
>>
>> And so I am fine if we don't want to do this stuff in kernel.
>>
>>> I thought we were aligned that any new overlays into the kernel today would
>>> only be for boot loader applied case.  Applying overlays at kernel runtime
>>> was out of scope at your request.
>>>
>>> Rob had requested that the overlays be test applied at build time.  I don't
>>> think there is any way to test the kernel runtime method at build time
>>> correct?
>>>
>>> Please clarify your concern and your suggested way forward.
>>
>> The kernel does some overlay testing currently (at kernel boot only,
>> not later), to see if the overlays get applied correctly or not, these
>> are the unit tests.
>>
>> What Frank is probably saying is that the unit-tests dtbs shouldn't
>> get used for testing fdtoverlay stuff. He isn't asking to support
>> runtime application of overlays, but to not do fdtoverlay testing in
>> the kernel.

Yes, Viresh is understanding my point.

>>
> 
> Thanks Viresh, that makes sense.  Sorry for the confusion Frank.

No problem Bill, communication by email is hard, and we end up
spending a lot of time getting to the point of common understanding,
it is the nature of the process.

-Frank