netdev - Re: [net-next-2.6 PATCH 2/3] fs_enet: Add support for MPC512x to fs

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Message-ID: <fa686aa41002100628x7ffc8fa9h3170f58387c5b67d@mail.gmail.com>
Date:	Wed, 10 Feb 2010 07:28:14 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Wolfgang Grandegger <wg@...ndegger.com>
Cc:	David Miller <davem@...emloft.net>, agust@...x.de,
	netdev@...r.kernel.org, dzu@...x.de, wd@...x.de, jcrigby@...il.com,
	kosmo@...ihalf.com, linuxppc-dev@...abs.org
Subject: Re: [net-next-2.6 PATCH 2/3] fs_enet: Add support for MPC512x to 
	fs_enet driver

On Wed, Feb 10, 2010 at 3:20 AM, Wolfgang Grandegger <wg@...ndegger.com> wrote:
> Wolfgang Grandegger wrote:
>> Hi David,
>>
>> David Miller wrote:
>>> From: Anatolij Gustschin <agust@...x.de>
>>> Date: Tue, 9 Feb 2010 15:23:17 +0100
>>>
>>>> In my understanding, in the ESP scsi driver the set of defines for
>>>> the register offsets is common for all chip drivers. The chip driver
>>>> methods for register access translate the offsets because the
>>>> registers on some chips are at different intervals (4-byte, 1-byte,
>>>> 16-byte for mac_esp.c). But the register order is the same for
>>>> different chips.
>>>>
>>>> In our case non only the register order is not the same for 8xx
>>>> FEC and 5121 FEC, but there are also other differences, different
>>>> reserved areas between several registers, some registers are
>>>> available only on 8xx and some only on 5121.
>>> That only means you would need to use a table based register address
>>> translation scheme, rather than a simple calculation.  Something
>>> like:
>>>
>>> static unsigned int chip_xxx_table[] =
>>> {
>>>      [GENERIC_REG_FOO]        = CHIP_XXX_FOO,
>>>      ...
>>> };
>>>
>>> static u32 chip_xxx_read_reg(struct chip *p, unsigned int reg)
>>> {
>>>      unsigned int reg_off = chip_xxx_table[reg];
>>>
>>>      return readl(p->regs + reg_off);
>>> }
>>>
>>> And this table can have special tokens in entries for
>>> registers which do not exist on a chip, so you can trap
>>> attempted access to them in these read/write handlers.
>>
>> Yes, that could be done, but to honest, I do not see any improvement in
>> respect to the previous patch where the register offset were defined via
>> pointers within a structure.
>>
>>> Please stop looking for excuses to fork this driver, a
>>> unified driver I think can be done cleanly.
>>
>> Other people suggested to fork the driver because it's getting too ugly.
>
> That said, I think there is consensus that it does not make sense, and
> it's even not possible, to provide a kernel image which runs on both,
> the 8xx and the mpc512x. Therefore, there is also no need for sharing
> this driver at run time. Compile time selection would allow a more
> elegant and transparent implementation. Would that be an acceptable
> solution?

I'm okay with compile time selection.

g.
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