On 1/12/21 2:46 PM, Rob Herring wrote:

On Tue, Jan 12, 2021 at 2:05 PM Frank Rowand [off-list ref] wrote:

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On 1/12/21 1:41 PM, Rob Herring wrote:

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On Tue, Jan 12, 2021 at 1:06 PM Frank Rowand [off-list ref] wrote:

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On 1/12/21 8:04 AM, Rob Herring wrote:

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On Mon, Jan 11, 2021 at 4:06 PM Frank Rowand [off-list ref] wrote:

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On 1/8/21 2:41 AM, Viresh Kumar wrote:

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Now that fdtoverlay is part of the kernel build, start using it to test
the unitest overlays we have by applying them statically.

The file overlay_base.dtb have symbols of its own and we need to apply
overlay.dtb to overlay_base.dtb alone first to make it work, which gives
us intermediate-overlay.dtb file.

The intermediate-overlay.dtb file along with all other overlays is them
applied to testcases.dtb to generate the master.dtb file.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

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.

This patch doesn't take away from any of that and it completely orthogonal.

Mea culpa.  I took the patch header comment at face value, and read more into
the header comment than what was written there.  I then skimmed the patch
instead of actually reading what it was doing.

I incorrectly _assumed_ (bad!) that the intent was to replace applying the
individual overlay dtb's with the master.dtb.  Reading more closely, I see
that the assumed final step of actually _using_ master.dtb does not exist.

So, yes, I agree that the patch as written is orthogonal to my concern.

My updated understanding is that this patch is attempting to use the existing
unittest overlay dts files as source to test fdtoverlay.  And that the resulting
dtb from fdtoverlay is not intended to be consumed by the kernel unittest.

The goal is not to test fdtoverlay. dtc unittests do that. The goal is
testing overlays we expect to be able to apply can actually apply and
doing this at build time. That's also the goal for all the 'real'
overlays which get added.

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I do not agree that this is a good approach to testing fdtoverlay.  The
unittest overlay dts files are constructed specifically to test various
parts of the kernel overlay code and dynamic OF code.  Some of the content
of the overlays is constructed to trigger error conditions in that code,
and thus will not be able to be processed without error by fdtoverlay.

Then those should be omitted.

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Trying to use overlay dts files that are constructed to test runtime kernel
code as fdtoverlay input data mixes two different test environments and
objectives.  If fdtoverlay test cases are desired, then fdtoverlay specific
dts files should be created.

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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.

If you (or more importantly someone else sending us patches) make
changes to the overlays, you can test that they apply at build time
rather than runtime. I'll take it! So please help on fixing the issue
because I want to apply this.

If the tests can be added to the upstream project, I would much prefer
they reside there.  If there is some reason a certain test is more
suited to be in the Linux kernel source tree then I also would like
it to be accepted here.

Again, this is just about doing sanity checks at build time rather
than *only* rely on runtime.

I'm fine with adding tests for applying overlays at build time (in
other words, tests of fdtoverlay).

Again, it's not tests of fdtoverlay. It's a test of the dts files. We
are testing that an overlay dts can apply to the base dts we claim it
applies. If the overlay dts has crap then we'll catch it.

We shouldn't accept overlays that can't apply to a base in the kernel
tree. That's either because it's broken or because the base doesn't
exist. With the exception of overlays designed to fail for tests,
unittest overlays should not be any different.

I understood the goal to be testing fdtoverlay.  I'll switch my mind
set to the goal being a test of dts files.

We already know that unittest overlays that are expected to be valid
can apply successfully.  The run time unittests already check for that.
I don't see any value in adding a build time test for the same thing
_for unittest overlay dts files_.  And I do see an ongoing maintenance
cost for _unittest overlay dts files_.

If you want to add build time tests for all (or some) non-unittest overlay
dts files, then I am not particularly opposed to that (but being aware that
an overlay dtb could apply on top of more than one base dtb, so there
is a possibility of an "explosion" of combinations to be maintained
in the build system).

I see value in having build time testing that overlay dtbs apply cleanly
on a base dtb.  I have heard frustration from the out of tree users of
overlays that apply the overlays via the bootloader, because if the
bootloader fails to apply an overlay it can be difficult to debug or
fix on the target computer.  Having a mechanism to specify what overlays
are intended to be applied to a base dtb, and verify that they do
apply would resolve some of those issues, assuming the boot loader
and fdtoverlay are consistent with each other.

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But the constraints on applying an overlay at build time are different
than the runtime constraints.

Like what specifically? Runtime is more constrained than build time.
Or at least it should be. It's not really and that's why we have
limited runtime applied overlay support.

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The existing unittest overlay dts files are not designed to test applying
overlays at build time.  Tests for fdtoverlay should be designed to test
that overlays that meet the build time constraints can be applied
properly by fdtoverlay, and that overlays that fail to meet those
constraints are rejected by fdtoverlay.

Trying to use the same data (dts) files for tests that have different
constraints is likely to make both tests more fragile when a data file
is modified for one environment without careful consideration of the
other environment.

We're not changing nor constraining the data files. Just adding
another sanity test on them.

For _unittest_ dts files, I see no value add.  And the cost of needing
to track _in the build system_ which unittest dts files are expected fail
to apply and which are expected to succeed.

-Frank

Rob