linux-kernel - Re: [PATCH v2] of/fdt: Remove redundant kbasename function call

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Date:   Mon, 25 Jan 2021 20:06:10 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>
Cc:     Qi Zheng <arch0.zheng@...il.com>,
        "frowand.list@...il.com" <frowand.list@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] of/fdt: Remove redundant kbasename function call

+LAKML given it's an Arm issue

On Mon, Jan 25, 2021 at 6:47 PM Chris Packham
<Chris.Packham@...iedtelesis.co.nz> wrote:
>
> Hi All,
>
> On 29/05/20 1:25 am, Qi Zheng wrote:
> > For version 1 to 3 of the device tree, this is the node full
> > path as a zero terminated string, starting with "/". The
> > following equation will not hold, since the node name has
> > been processed in the fdt_get_name().
> >
> >       *pathp == '/'
> >
> > For version 16 and later, this is the node unit name only
> > (or an empty string for the root node). So the above
> > equation will still not hold.
> >
> > So the kbasename() is redundant, just remove it.
> >
> > Signed-off-by: Qi Zheng <arch0.zheng@...il.com>
> > ---
> >
> > Change in v2:
> >       remove another kbasename() also.
> >
> >   drivers/of/fdt.c | 4 ----
> >   1 file changed, 4 deletions(-)
> >
> > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> > index 38619e9ef6b2..4602e467ca8b 100644
> > --- a/drivers/of/fdt.c
> > +++ b/drivers/of/fdt.c
> > @@ -643,8 +643,6 @@ int __init of_scan_flat_dt(int (*it)(unsigned long node,
> >            offset = fdt_next_node(blob, offset, &depth)) {
> >
> >               pathp = fdt_get_name(blob, offset, NULL);
> > -             if (*pathp == '/')
> > -                     pathp = kbasename(pathp);
> >               rc = it(offset, pathp, depth, data);
> >       }
> >       return rc;
> > @@ -671,8 +669,6 @@ int __init of_scan_flat_dt_subnodes(unsigned long parent,
> >               int rc;
> >
> >               pathp = fdt_get_name(blob, node, NULL);
> > -             if (*pathp == '/')
> > -                     pathp = kbasename(pathp);
> >               rc = it(node, pathp, data);
> >               if (rc)
> >                       return rc;
>
> I'm trying to keep our boards up to date with newer kernels.
>
> I've just hit a problem on an older board that uses
> CONFIG_ARM_APPENDED_DTB and has a number of command line args passed up
> from the bootloader that are required for a successful boot.
>
> I'm stepping through kernel versions in the hope that keeping things
> running is easier in smaller increments I'm up to v5.8. I'm not
> currently able to check a newer kernel on this board but looking at the
> code the problem still seems to exist in the latest tree.
>
> early_init_dt_scan_chosen() searches for "chosen" prior to this change
> the "/chosen" node that gets inserted by atags_to_fdt.c but with this
> change it can't find it and fails to boot.

Given this code works for normal cases, I'm guessing the problem is in
atags_to_fdt.c or libfdt. Is it possible to add an empty chosen node
to the DT and see if that makes any difference.

Rob