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

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Date:	Wed, 10 Feb 2010 10:15:54 +0100
From:	Wolfgang Grandegger <wg@...ndegger.com>
To:	David Miller <davem@...emloft.net>
CC:	agust@...x.de, netdev@...r.kernel.org, dzu@...x.de, wd@...x.de,
	jcrigby@...il.com, kosmo@...ihalf.com, linuxppc-dev@...abs.org,
	grant.likely@...retlab.ca
Subject: Re: [net-next-2.6 PATCH 2/3] fs_enet: Add support for MPC512x to
 fs_enet driver

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.

Wolfgang.
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