Re: [PATCH] libata: automatically use DMADIR if drive/bridge requires it

[Jeff Garzik <jgarzik@pobox.com>]

Mark Lord wrote:
> Albert Lee wrote:
>> Tejun Heo wrote:
>>> Back in 2.6.17-rc2, a libata module parameter was added for 
>>> atapi_dmadir.
>>>
>>> That's nice, but most SATA devices which need it will tell us about it
>>> in their IDENTIFY PACKET response, as bit-15 of word-62 of the
>>> returned data (as per ATA7, ATA8 specifications).
>>>
>>> So for those which specify it, we should automatically use the DMADIR 
>>> bit.
>>> Otherwise, disc writing will fail by default on many SATA-ATAPI drives.
>>>
>>> This patch adds ATA_DFLAG_DMADIR and make ata_dev_configure() set it
>>> if atapi_dmadir is set or identify data indicates DMADIR is necessary.
>>> atapi_xlat() is converted to check ATA_DFLAG_DMADIR before setting
>>> DMADIR.
>>>
>>> Original patch is from Mark Lord.
>>>
>>> Signed-off-by: Tejun Heo <htejun@gmail.com>
>>> Cc: Mark Lord <mlord@pobox.com>
>>> ---
>>> I don't have a bridge which sets DMADIR but so only checked atapi_dmadir
>>> parameter.  Thanks.
>>>
>>
>> The patch looks good. However, it seems there is no realworld IDE-to-SATA
>> bridge that requires DMADIR and also mangles IDENTIFY PACKET bit-15 of
>> word-62 to indicate its presence.
>>
>>> From the previous test of the IDE-to-SATA bridges, only the Sil 3611
>> requires the host software to hint on ATAPI DMADIR. But Sil 3611 doesn't
>> mangle IDENTIFY PACKET word-62:
>> http://www.spinics.net/lists/linux-ide/msg01514.html
> ..
> 
> Ahh, great!  We have "history" here!
> 
> But there are more SATA bridges out there than the ones Alber has there
> (SiI 3611/3811, Marvell 88i8030/88SA8040, Acard ARC770, JMicron JM20330).
> 
> There's the Marvell 88SA8050, and I have a funky looking thing here
> that says "SataLink SPiF223A" on it (????).  I wonder what it does?
> And how many other ones are there?
> 
> The Word62 patch (from Tejun) is simple enough that the "complexity"
> point from before really doesn't hold water.

I'm going to apply Tejun's patch.  It's fine (as I noted I conditionally 
ACK'd your original patch).

My opinion, though, it that this is merely coding to the spec, rather 
than making a bunch of real-world hardware work.  All the SATA<->PATA 
bridges I have, that support ATAPI, do not flag DMADIR.

	Jeff