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    SubjectRe: [PATCH 1/2] of/fdt: Allow architectures to override CONFIG_CMDLINE logic
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    On Fri, 07 Sep 2018 13:29:03 PDT (-0700), robh+dt@kernel.org wrote:
    > On Fri, Sep 7, 2018 at 1:55 PM Paul Burton <paul.burton@mips.com> wrote:
    >>
    >> The CONFIG_CMDLINE-related logic in early_init_dt_scan_chosen() falls
    >> back to copying CONFIG_CMDLINE into boot_command_line/data if the DT has
    >> a /chosen node but that node has no bootargs property or a bootargs
    >> property of length zero.
    >
    > The Risc-V guys found a similar issue if chosen is missing[1]. I
    > started a patch[2] to address that, but then looking at the different
    > arches wasn't sure if I'd break something. I don't recall for sure,
    > but it may have been MIPS that worried me.

    IIRC we actually determined it didn't even work correctly on RISC-V, but I
    never actually got the time to figure out why and then forgot about it. Sorry!

    >
    >> This is problematic for the MIPS architecture because we support
    >> concatenating arguments from either the DT or the bootloader with those
    >> from CONFIG_CMDLINE, but the behaviour of early_init_dt_scan_chosen()
    >> gives us no way of knowing whether boot_command_line contains arguments
    >> from DT or already contains CONFIG_CMDLINE. This can lead to us
    >> concatenating CONFIG_CMDLINE with itself, duplicating command line
    >> arguments which can be problematic (eg. for earlycon which will attempt
    >> to register the same console twice & warn about it).
    >
    > If CONFIG_CMDLINE_EXTEND is set, you know it contains CONFIG_CMDLINE.
    > But I guess part of the problem is MIPS using its own kconfig options.
    >
    >> Move the CONFIG_CMDLINE-related logic to a weak function that
    >> architectures can provide their own version of, such that we continue to
    >> use the existing logic for architectures where it's suitable but also
    >> allow MIPS to override this behaviour such that the architecture code
    >> knows when CONFIG_CMDLINE is used.
    >
    > More arch specific functions is not what I want. Really, all the
    > cmdline manipulating logic doesn't belong in DT code, but it shouldn't
    > be in the arch specific code either IMO. Really it should be some
    > common kernel function which calls into the DT code to retrieve the DT
    > bootargs and that's it. Then you can skip calling that kernel function
    > if you really need non-standard handling.
    >
    > Perhaps you should consider filling DT bootargs with the cmdline from
    > bootloader. IOW, make the legacy case look like the non-legacy case
    > early, and then the kernel doesn't have to deal with both cases later
    > on.
    >
    > Rob
    >
    > [1] https://lkml.org/lkml/2018/3/14/701
    > [2] git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git dt/cmdline

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