linux-kernel - Re: [PATCH] [RFC] drm: rcar-du: keep temporary dtb files around during build

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Date:   Fri, 23 Mar 2018 02:47:27 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Frank.Rowand@...y.com, Arnd Bergmann <arnd@...db.de>,
        David Airlie <airlied@...ux.ie>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>
Subject: Re: [PATCH] [RFC] drm: rcar-du: keep temporary dtb files around
 during build

2018-03-23 0:13 GMT+09:00 Geert Uytterhoeven <geert@...ux-m68k.org>:
> Hi Laurent,
>
> CC Yamada-san
>
> On Thu, Mar 22, 2018 at 3:50 PM, Laurent Pinchart
> <laurent.pinchart@...asonboard.com> wrote:
>> On Thursday, 22 March 2018 16:26:22 EET Geert Uytterhoeven wrote:
>>> On Fri, Mar 16, 2018 at 2:39 AM,  <Frank.Rowand@...y.com> wrote:
>>> > On Thursday, March 15, 2018 8:37 AM, Arnd Bergmann wrote:
>>> >> The *.dtb and *.dtb.S files get removed by 'make' during the build
>>> >> process, and later seem to be missed during the 'modpost' stage:
>>> >>
>>> >> rm drivers/gpu/drm/rcar-du/rcar_du_of_lvds_r8a7795.dtb
>>> >> drivers/gpu/drm/rcar-du/rcar_du_of_lvds_r8a7791.dtb
>>> >> drivers/gpu/drm/rcar-du/rcar_du_of_lvds_r8a7791.dtb.S
>>> >> drivers/gpu/drm/rcar-du/rcar_du_of_lvds_r8a7795.dtb.S
>>> >> drivers/gpu/drm/rcar-du/rcar_du_of_lvds_r8a7790.dtb.S
>>> >> drivers/gpu/drm/rcar-du/rcar_du_of_lvds_r8a7793.dtb
>>> >> drivers/gpu/drm/rcar-du/rcar_du_of_lvds_r8a7796.dtb
>>> >> drivers/gpu/drm/rcar-du/rcar_du_of_lvds_r8a7790.dtb
>>> >> drivers/gpu/drm/rcar-du/rcar_du_of_lvds_r8a7796.dtb.S
>>> >> drivers/gpu/drm/rcar-du/rcar_du_of_lvds_r8a7793.dtb.S
>>> >> WARNING: could not open
>>> >> drivers/gpu/drm/rcar-du/rcar_du_of_lvds_r8a7790.dtb.S: No such file or
>>> >> directory
>>> >>
>>> >> As a workaround, this adds all those files to the 'extra-y' target list,
>>> >> but that's really ugly. Any ideas for a better fix?
>>> >
>>> > Does this work for you (untested, but the way it is done in
>>> > drivers/of/unittest-data/Makefile):
>>> >
>>> > .PRECIOUS: \
>>> >
>>> >         $(obj)/%.dtb.S \
>>> >         $(obj)/%.dtb
>>>
>>> Shouldn't that just be moved to scripts/Makefile.lib, just above the rule
>>> to make dtb.S, like is done for other precious objects?
>>
>> Without any implied acknowledgment that keeping those intermediate files is
>> the right solution (I don't claim to master the kernel build system), I think
>
> Me neither, but I think it is.
>
> Cfr. .y => .tab.c => .tab.o with .tab.c marked PRECIOUS.
>
>> such a rule would indeed be better in a core Makefile, as the rules to build
>> the .dtb.o file comes from the core too. Could another option be to create a
>> rule to compile a .dtb.o from the .dts file directly without going through
>> intermediate files that will be removed automatically ?
>
> Such a rules needs to execute two commands, which is more tricky, considering
> error handling.
> It's easier (to get right) to have two separate rules, and let make chain them
> automatically.
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds



This has been in my TODO list for a while,
but I have not had time to finish it.


Some people use .PRECIOUS to suppress file removal,
but it is wrong IMO.

.SECONDARY is the right one, but one problem is,
this does not work with pattern rules.

I will send a patch soon for the core improvement.


-- 
Best Regards
Masahiro Yamada