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From:   Rob Herring <robh+dt@kernel.org>
Date:   Fri, 15 Feb 2019 13:44:26 -0600
Message-ID: <CAL_JsqJ8967v0-1scuWY0nMngiO=TxNL_bxgsP=hzO9SU-n2NQ@mail.gmail.com>
Subject: Re: [PATCH v1 1/1] of: unittest: unflatten device tree on UML when testing
To:     Brendan Higgins <brendanhiggins@google.com>
Cc:     Frank Rowand <frowand.list@gmail.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        devicetree <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Fri, Feb 15, 2019 at 3:49 AM Brendan Higgins
<brendanhiggins@google.com> wrote:
>
> On Thu, Feb 14, 2019 at 6:48 PM Frank Rowand <frowand.list@gmail.com> wrote:
> >
> > On 2/14/19 5:26 PM, Brendan Higgins wrote:
> > > On Thu, Feb 14, 2019 at 4:10 PM Frank Rowand <frowand.list@gmail.com> wrote:
> > >>
> > >> On 2/12/19 10:53 AM, Brendan Higgins wrote:
> > >>> UML supports enabling OF, and is useful for running the device tree
> > >>> tests, so add support for unflattening device tree blobs so we can
> > >>> actually use it.
> > >>>
> > >>> Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
> > >>> ---
> > >>>  drivers/of/unittest.c | 3 +++
> > >>>  1 file changed, 3 insertions(+)
> > >>>
> > >>> diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
> > >>> index 84427384654d5..effa4e2b9d992 100644
> > >>> --- a/drivers/of/unittest.c
> > >>> +++ b/drivers/of/unittest.c
> > >>> @@ -2527,6 +2527,9 @@ static int __init of_unittest(void)
> > >>>       }
> > >>>       of_node_put(np);
> > >>>
> > >>> +     if (IS_ENABLED(CONFIG_UML))
> > >>> +             unflatten_device_tree();
> > >>> +
> > >>>       pr_info("start of unittest - you will see error messages\n");
> > >>>       of_unittest_check_tree_linkage();
> > >>>       of_unittest_check_phandles();
> > >>>
> > >>
> > >> (Insert my usual disclaimer that I am clueless about UML, I still need to learn
> > >> about it...)
> > >>
> > >> This does not look correct to me.
> > >>
> > >> A few lines earlier in of_unittest(), the live devicetree needs to exist for
> > >> unittest_data_data() and a few of_*() functions to succeed.  So it seems
> > >> that the unflatten_device_tree() for uml should be at the beginning of
> > >> of_unittest().
> > >
> > > It is true that other functions ahead of it depend on the presence of
> > > a device tree, but an unflattened tree does get linked in somewhere
> > > else. Despite that, this is needed for overlay_base_root. I got
> > > similar behavior if you don't link in a flattened device tree on x86.
> > > Thus, the order in which you call them doesn't actually seem to
> > > matter. I found no difference from changing the order in UML myself.
> > >
> > > Without my patch we get the following error,
> > > ### dt-test ### FAIL of_unittest_overlay_high_level():2372
> > > overlay_base_root not initialized
> > > ### dt-test ### end of unittest - 219 passed, 1 failed
> > >
> > > With my patch we get:
> > > ### dt-test ### end of unittest - 224 passed, 0 failed
> >
> > Thanks for reporting both the failure and the success cases,
> > that helps me understand a little bit better.
> >
> > If instead of the above patch, if you add the following (untested,
> > not even compile tested) to the beginning of of_unittest():
> >
> >         if (IS_ENABLED(CONFIG_UML))
> >                 unittest_unflatten_overlay_base();
> >
> > does that also result in a good test result of:
> >
> >         ### dt-test ### end of unittest - 224 passed, 0 failed
>
> Yep, I just tried it. It works as you suspected.
>
> >
> > I think I need to find some time to build and boot a UML kernel soon.
>
> It's really no big deal, just copy the .config I sent and build with
> `make ARCH=um` then you "boot" the kernel with `./linux` (note this
> will mess up your terminal settings); that's it! (Shameless plug: you
> can also try it out with the KUnit patchset with
> `./tools/testing/kunit/kunit.py --timeout=30 --jobs=12 --defconfig`,
> which builds the kernel with a pretty similar config, boots the
> kernel, and then parses the output for you. ;-) )
>
> >
> > My current _guess_ is that the original problem was not a failure to
> > unflatten any present devicetree in UML but instead that the UML
> > kernel does not call unflatten_device_tree() and thus fails to
> > indirectly call unittest_unflatten_overlay_base(), which is
> > called by unflatten_device_tree().
>
> I think you are right. Sorry for not noticing this before making my
> change. Since it was pretty much the only architecture (the only one I
> care about) that does not unflatten DT, I assumed that was the
> problem. I didn't put too much thought into it after that point beyond
> making sure that it did what I wanted.
>
> >
> > unittest_unflatten_overlay_base() is an unfortunate wart that I
> > added, but I don't have a better alternative yet.
>
> Hey, I get it. No worries.
>
> In any case, it seems like unittest_unflatten_overlay_base() is the
> right function to call there. I will send out patch. Do you want me to
> send a patch on top of this one, or do you want to revert this one and
> for me to send a v2 follow up to this patch? I don't care either way,
> whatever you guys prefer.

I'll drop or revert the existing one, so against mainline is good.

Rob