[PATCH RFC] pata_platform: add 8 bit data io support

[Wang Jian]

Benjamin Herrenschmidt 写道:
> On Sun, 2008-10-12 at 02:00 +0800, Wang Jian wrote:
>> To avoid adding another rare used ata_port member, new bit is added to
>> ata_port->flags.
>>
>> Originally, I hacked pata_platform to make it 8bit only to support 8bit
>> data wired CF card. This patch is more generic.
>>
>> With this patch, __pata_platform_probe() interface is changed, and
>> pata_of_platform is broken, so a small patch is needed.
>>
>> Signed-off-by: Wang Jian <lark at linux.net.cn>
>> ---
> 
> A couple of things. First I would personally prefer (but I'm not the
> libata maintainer so it's up to Jeff ...) if you had a separate patch
> that adds the 8-bit support to libata core first, and then a patch that
> modifies pata_platform.

I will do that if my 8-bit mode patch is done right technically.

> 
> Then, in order to avoid breaking bisection, I would like you to fixup
> pata_of_platform in the same patch that modifies __pata_platform_probe
> so there is no breakage in between patches.

Yes.

> 
> Now, regarding the patch itself, if the core grows a 8-bit flag, then
> I strongly suspect the core should also grow the 8-bit xfer function
> rather than having it hidden in pata_platform.

This is the main reason I send a single RFC patch. Where to add 8-bit
mode should be decided first.

Because 8-bit mode is mostly used for embedded devices, my opinion is
8-bit mode in pata_platform is enough.

However, look at pata_platform_data_xfer() I added, the code can be
merged into ata_sff_data_xfer() of libata-sff.c easily. Moving the
code there is trivial if necessary.

Another problem should be addressed: using flags v.s. using data_width
member. I add a bit to indicate 8 bit mode, but this seems to be a problem
for future 32 bit I/O support in libata.