linux-kernel - Re: [PATCH 7/7] MIPS: boot: rebuild ITB when contained DTB is updated

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Message-ID: <20180620002647.u2d7t3vzc2yinkft@pburton-laptop>
Date:   Tue, 19 Jun 2018 17:26:47 -0700
From:   Paul Burton <paul.burton@...s.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
CC:     Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        "linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
        Kees Cook <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/7] MIPS: boot: rebuild ITB when contained DTB is updated

Hi Masahiro,

On Mon, Apr 16, 2018 at 07:47:47AM -0700, Masahiro Yamada wrote:
> Since now, the unnecessary rebuild of ITB has been fixed.  Another
> problem to be taken care of is, missed rebuild of ITB.
> 
> For example, board-boston.its.S includes boston.dtb by the /incbin/
> directive.  If boston.dtb is updated, vmlinux.*.dtb must be rebuilt.
> Currently, the dependency between ITB and contained DTB files is not
> described anywhere.  Previously, this problem was hidden since
> vmlinux.*.itb was always rebuilt even if nothing is updated.  By
> fixing the spurious rebuild, this is a real problem now.
> 
> Use the same strategy for automatic generation of the header file
> dependency.  DTC works as a backend of mkimage, and DTC supports -d
> option.  It outputs the dependencies, including binary files pulled
> by the /incbin/ directive.
> 
> The implementation is simpler than cmd_dtc in scripts/Makefile.lib
> since we do not need CPP here.  Just pass -d $(depfile) to DTC, and
> let the resulted $(depfile) processed by fixdep.
> 
> It might be unclear why "$(obj)/dts/%.dtb: ;" is needed.  With this
> commit, *.cmd files will contain dependency on DTB files.  In the
> next invocation of build, the *.cmd files will be included, then
> Make will try to find a rule to update *.dtb files.  Unfortunately,
> it is found in scripts/Makefile.lib.  The build rule of $(obj)/%.dtb
> is invoked by if_changed_dep, so it needs to include *.cmd files
> of DTB, but they are not included because we are in arch/mips/boot,
> but those *.cmd files reside in arch/mips/boot/dts/*/.  Cancel the
> pattern rule in scripts/Makefile.lib to suppress unneeded rebuilding
> of DTB.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
> 
>  arch/mips/boot/Makefile | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)

Thanks - this looks good to me except that it starts outputting a "Don't
know how to preprocess itb-image" message after building the .itb.

I presume we just need an extra case adding to ksym_dep_filter. Do you
want to add that in & resubmit this one?

Thanks,
    Paul