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Date: Wed, 1 Dec 2010 08:47:19 -0500
From: Josh Boyer <jwboyer@linux.vnet.ibm.com>
To: Joachim Foerster <JOFT@gmx.de>
Subject: Re: _extending_ platform support options?
Message-ID: <20101201134719.GA1053@zod.rchland.ibm.com>
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On Wed, Dec 01, 2010 at 02:25:43PM +0100, Joachim Foerster wrote:
>Hi all,
>
>currently I'm wondering what the preferred/recommend way of
>_extending_ an existing "Platform support" option is?
>
>We are working with custom design/boards based on Virtex4/5. So we
>are primarily using the  CONFIG_XILINX_VIRTEX*_GENERIC_BOARD options.
>In our case we have some special needs, like custom ppc_md.restart(),
>ppc_md.power_off() or ppc_md.show_cpuinfo().
>
>Till now, we just duplicated arch/powerpc/platforms/4?x/virtex.c and
>added our special stuff. Properly renaming everything, etc ...
>
>An alternative could be to add a virtex_my.c which extends virtex.c, like this
>(also like virtex_ml510.c extends virtex.c):
>
>static void virtex_my_show_cpuinfo(struct seq_file *m)
>{
>	seq_printf(m, something);
>}
>
>static int __init virtex_mle_init(void)
>{
>	ppc_md.show_cpuinfo = virtex_my_show_cpuinfo;
>	return 0;
>}
>machine_core_initcall(virtex, virtex_my_init);
>
>Though, to me, it does not seem really OK to assign ppc_md members
>that way. The original struct machdep for "virtex" (which is defined
>in virtex.c with define_machine()) is not adjusted either. Ok, we
>could modify that one, too.
>Especially I'm not sure if it is OK to use machine_core_initcall() for such modifications.
>
>So my question is: Is there any recommended way for doing such
>"extensions"? Or is it OK to just duplicate virtex.c (which does not
>seem really OK, too)?

Duplicate it as you have done, naming the file something unique.  We try
to prevent unnecessary duplication of code, but sometimes it's cleaner
to just have a separate board file instead.

josh