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

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Date:   Tue, 26 Jan 2021 02:34:25 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Rob Herring <robh+dt@...nel.org>
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


On 26/01/21 3:06 pm, Rob Herring wrote:
> +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.

It might be related tot this snippet of libfdt

const char *fdt_get_name(const void *fdt, int nodeoffset, int *len)
{

...

         if (!can_assume(LATEST) && fdt_version(fdt) < 0x10) {
                 /*
                  * For old FDT versions, match the naming conventions 
of V16:
                  * give only the leaf name (after all /). The actual tree
                  * contents are loosely checked.
                  */
                 const char *leaf;
                 leaf = strrchr(nameptr, '/');
                 if (leaf == NULL) {
                         err = -FDT_ERR_BADSTRUCTURE;
                         goto fail;
                 }
                 nameptr = leaf+1;
         }

...

}

On my system that if evaluates to 0

> Is it possible to add an empty chosen node
> to the DT and see if that makes any difference.
I'll give that a try.